This chapter expands on the information introduced in [simple-project]. We’re going to create a simple project generated with the Maven Archetype plugin, add some dependencies, add some source code, and customize the project to suit our needs. By the end of this chapter, you will know how to start using Maven to create real projects.
We’ll be developing a useful program that interacts with a Yahoo Weather web service. Although you should be able to follow along with this chapter without the example source code, we recommend that you download a copy of the code to use as a reference. This chapter’s example project may be downloaded with the book’s example code at:
http://books.sonatype.com/mvnex-book/mvnex-examples.zip
Unzip this archive in any directory, and then go to the ch-custom/
directory. There you will see a directory named simple-weather/,
which contains the Maven project developed in this chapter.
Before we start customizing this project, let’s take a step back and talk about the Simple Weather project. What is it? It’s a contrived example, created to demonstrate some of the features of Maven. It is an application that is representative of the kind you might need to build. The Simple Weather application is a basic command-line-driven application that takes a zip code and retrieves some data from the Yahoo Weather RSS feed. It then parses the result and prints the result to standard output.
We chose this example for a number of reasons. First, it is straightforward. A user supplies input via the command line, the app takes that zip code, makes a request to Yahoo Weather, parses the result, and formats some simple data to the screen. This example is a simple main() function and some supporting classes; there is no enterprise framework to introduce and explain, just XML parsing and some logging statements. Second, it gives us a good excuse to introduce some interesting libraries such as Velocity, Dom4J, and Log4J. Although this book is focused on Maven, we won’t shy away from an opportunity to introduce interesting utilities. Lastly, it is an example that can be introduced, developed, and deployed in a single chapter.
Before you build this application, you should know something about the Yahoo Weather RSS feed. To start with, the service is made available under the following terms:
The feeds are provided free of charge for use by individuals and nonprofit organizations for personal, noncommercial uses. We ask that you provide attribution to Yahoo Weather in connection with your use of the feeds.
In other words, if you are thinking of integrating these feeds into your commercial web site, think again—this feed is for personal, noncommercial use. The use we’re encouraging in this chapter is personal educational use. For more information about these terms of service, see the Yahoo Weather! API documentation here: http://developer.yahoo.com/weather/.
First, let’s use the Maven Archetype plugin to create a basic skeleton
for the Simple Weather project. Execute the following command to
create a new project, press enter to use the default
maven-archetype-quickstart and the latest version of the archetype,
and then enter "Y" to confirm and generate the new project.
Note that the number for the archetype will be different on your execution:
$ mvn archetype:generate -DgroupId=org.sonatype.mavenbook.custom \
-DartifactId=simple-weather \
-Dversion=1.0
[INFO] Preparing archetype:generate
...
[INFO] [archetype:generate {execution: default-cli}]
[INFO] Generating project in Interactive mode
[INFO] No archetype defined. Using maven-archetype-quickstart \
(org.apache.maven.archetypes:maven-archetype-quickstart:1.0)
Choose archetype:
...
16: internal -> maven-archetype-quickstart ()
...
Choose a number: (...) 16: : 16
Confirm properties configuration:
groupId: org.sonatype.mavenbook.custom
artifactId: simple-weather
version: 1.0
package: org.sonatype.mavenbook.custom
Y: : Y
[INFO] Parameter: groupId, Value: org.sonatype.mavenbook.custom
[INFO] Parameter: packageName, Value: org.sonatype.mavenbook.custom
[INFO] Parameter: package, Value: org.sonatype.mavenbook.custom
[INFO] Parameter: artifactId, Value: simple-weather
[INFO] Parameter: basedir, Value: /private/tmp
[INFO] Parameter: version, Value: 1.0
[INFO] BUILD SUCCESSFUL
Once the Maven Archetype plugin creates the project, go into the
simple-weather directory and take a look at the pom.xml file. You
should see the XML document that’s shown in
Initial POM for the simple-weather Project.
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.sonatype.mavenbook.custom</groupId>
<artifactId>simple-weather</artifactId>
<packaging>jar</packaging>
<version>1.0</version>
<name>simple-weather</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
</project>
Next, you will need to configure the Maven Compiler plugin to target Java 5. To do this, add the build element to the initial POM as shown in POM for the simple-weather Project with Compiler Configuration.
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.sonatype.mavenbook.custom</groupId>
<artifactId>simple-weather</artifactId>
<packaging>jar</packaging>
<version>1.0</version>
<name>simple-weather</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
Notice that we passed in the version parameter to the
archetype:generate goal. This overrides the default value of
1.0-SNAPSHOT. In this project, we’re developing the 1.0 version of
the simple-weather project as you can see in the pom.xml version
element.
Before we start writing code, let’s customize the project information a bit. We want to add some information about the project’s license, the organization, and a few of the developers associated with the project. This is all standard information you would expect to see in most projects. Adding Organizational, Legal, and Developer Information to the pom.xml shows the XML that supplies the organizational information, the licensing information, and the developer information.
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/maven-v4_0_0.xsd">
...
<name>simple-weather</name>
<url>http://www.sonatype.com</url>
<licenses>
<license>
<name>Apache 2</name>
<url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
<distribution>repo</distribution>
<comments>A business-friendly OSS license</comments>
</license>
</licenses>
<organization>
<name>Sonatype</name>
<url>http://www.sonatype.com</url>
</organization>
<developers>
<developer>
<id>jason</id>
<name>Jason Van Zyl</name>
<email>jason@maven.org</email>
<url>http://www.sonatype.com</url>
<organization>Sonatype</organization>
<organizationUrl>http://www.sonatype.com</organizationUrl>
<roles>
<role>developer</role>
</roles>
<timezone>-6</timezone>
</developer>
</developers>
...
</project>
The ellipses in Adding Organizational, Legal, and Developer Information to the pom.xml are shorthand for an
abbreviated listing. When you see a pom.xml with “…” and “…”
directly after the project element’s start tag and directly before
the project element’s end tag, this implies that we are not showing
the entire pom.xml file. In this case the licenses,
organization, and developers elements were all added before the
dependencies element.
The Simple Weather application is going to have to complete the
following three tasks: retrieve XML data from Yahoo Weather, parse
the XML from Yahoo, and then print formatted output to standard
output. To accomplish these tasks, we have to introduce some new
dependencies to our project’s pom.xml. To parse the XML response
from Yahoo, we’re going to be using Dom4J and Jaxen, to format the
output of this command-line program we are going to be using Velocity,
and we will also need to add a dependency for Log4J which we will be
using for logging. After we add these dependencies, our dependencies
element will look like the following example.
<project>
[...]
<dependencies>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.14</version>
</dependency>
<dependency>
<groupId>dom4j</groupId>
<artifactId>dom4j</artifactId>
<version>1.6.1</version>
</dependency>
<dependency>
<groupId>jaxen</groupId>
<artifactId>jaxen</artifactId>
<version>1.1.1</version>
</dependency>
<dependency>
<groupId>velocity</groupId>
<artifactId>velocity</artifactId>
<version>1.5</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
[...]
</project>
As you can see above, we’ve added four more dependency elements in
addition to the existing element which was referencing the test
scoped dependency on JUnit. If you add these dependencies to the
project’s pom.xml file and then run mvn install, you will see
Maven downloading all of these dependencies and other transitive
dependencies to your local Maven repository.
How did we find these dependencies? Did we just “know” the appropriate
groupId and artifactId values? Some of the dependencies are so
widely used (like Log4J) that you’ll just remember what the groupId
and artifactId are every time you need to use them. Velocity, Dom4J,
and Jaxen were all located using the searching capability on
http://repository.sonatype.org. This
is a public Sonatype Nexus instance which provides a search interface
to various public Maven repositories, you can use it to search for
dependencies. To test this for yourself, load
http://repository.sonatype.org and
search for some commonly used libraries such as Hibernate or the
Spring Framework. When you search for an artifact on this site, it
will show you an artifactId and all of the versions known to the
central Maven repository. Clicking on the details for a specific
version will load a page that contains the dependency element you’ll
need to copy and paste into your own project’s pom.xml. If you need
to find a dependency, you’ll want to check out
repository.sonatype.org, as you’ll
often find that certain libraries have more than one groupId. With
this tool, you can make sense of the Maven repository.
The Simple Weather command-line application consists of five Java classes.
- org.sonatype.mavenbook.weather.Main
-
The Main class contains a static main() method: the entry point for this system.
- org.sonatype.mavenbook.weather.Weather
-
The Weather class is a straightforward Java bean that holds the location of our weather report and some key facts, such as the temperature and humidity.
- org.sonatype.mavenbook.weather.YahooRetriever
-
The YahooRetriever class connects to Yahoo Weather and returns an InputStream of the data from the feed.
- org.sonatype.mavenbook.weather.YahooParser
-
The YahooParser class parses the XML from Yahoo Weather and returns a Weather object.
- org.sonatype.mavenbook.weather.WeatherFormatter
-
The WeatherFormatter class takes a Weather object, creates a VelocityContext, and evaluates a Velocity template.
Although we won’t dwell on the code here, we will provide all the necessary code for you to get the example working. We assume that most readers have downloaded the examples that accompany this book, but we’re also mindful of those who may wish to follow the example in this chapter step-by-step. The sections that follow list classes in the simple-weather project. Each of these classes should be placed in the same package: org.sonatype.mavenbook.weather.
Let’s remove the App and the AppTest classes created by
archetype:generate and add our new package. In a Maven project, all
of a project’s source code is stored in src/main/java. From the base
directory of the new project, execute the following commands:
$ cd src/test/java/org/sonatype/mavenbook/custom $ rm AppTest.java $ cd ../../../../../../.. $ cd src/main/java/org/sonatype/mavenbook/custom $ rm App.java $ cd .. $ mkdir weather $ cd weather
This creates a new package named org.sonatype.mavenbook.weather. Now
we need to put some classes in this directory. Using your favorite
text editor, create a new file named Weather.java with the contents
shown in Simple Weather’s Weather Model Object.
package org.sonatype.mavenbook.weather;
public class Weather {
private String city;
private String region;
private String country;
private String condition;
private String temp;
private String chill;
private String humidity;
public Weather() {}
public String getCity() { return city; }
public void setCity(String city) {
this.city = city;
}
public String getRegion() { return region; }
public void setRegion(String region) {
this.region = region;
}
public String getCountry() { return country; }
public void setCountry(String country) {
this.country = country;
}
public String getCondition() { return condition; }
public void setCondition(String condition) {
this.condition = condition;
}
public String getTemp() { return temp; }
public void setTemp(String temp) {
this.temp = temp;
}
public String getChill() { return chill; }
public void setChill(String chill) {
this.chill = chill;
}
public String getHumidity() { return humidity; }
public void setHumidity(String humidity) {
this.humidity = humidity;
}
}
The Weather class defines a simple bean that is used to hold the weather information parsed from the Yahoo Weather feed. This feed provides a wealth of information, from the sunrise and sunset times to the speed and direction of the wind. To keep this example as simple as possible, the Weather model object keeps track of only the temperature, chill, humidity, and a textual description of current conditions.
Now, in the same directory, create a file named Main.java. This
Main class will hold the static main() method—the entry point
for this example.
package org.sonatype.mavenbook.weather;
import java.io.InputStream;
import org.apache.log4j.PropertyConfigurator;
public class Main {
public static void main(String[] args) throws Exception {
// Configure Log4J
PropertyConfigurator
.configure(Main.class.getClassLoader()
.getResource("log4j.properties"));
// Read the zip code from the command line
// (if none supplied, use 60202)
String zipcode = "60202";
try {
zipcode = args[0];
} catch( Exception e ) {}
// Start the program
new Main(zipcode).start();
}
private String zip;
public Main(String zip) {
this.zip = zip;
}
public void start() throws Exception {
// Retrieve Data
InputStream dataIn = new YahooRetriever().retrieve( zip );
// Parse Data
Weather weather = new YahooParser().parse( dataIn );
// Format (Print) Data
System.out.print( new WeatherFormatter().format( weather ) );
}
}
The main() method shown above configures Log4J by retrieving a resource from the classpath. It then tries to read a zip code from the command line. If an exception is thrown while it is trying to read the zip code, the program will default to a zip code of 60202. Once it has a zip code, it instantiates an instance of Main and calls the start() method on an instance of Main. The start() method calls out to the YahooRetriever to retrieve the weather XML. The YahooRetriever returns an InputStream which is then passed to the YahooParser. The YahooParser parses the Yahoo Weather XML and returns a Weather object. Finally, the WeatherFormatter takes a Weather object and spits out a formatted String which is printed to standard output.
Create a file named YahooRetriever.java in the same directory with
the contents shown in Simple Weather’s YahooRetriever Class.
package org.sonatype.mavenbook.weather;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import org.apache.log4j.Logger;
public class YahooRetriever {
private static Logger log = Logger.getLogger(YahooRetriever.class);
public InputStream retrieve(String zipcode) throws Exception {
log.info( "Retrieving Weather Data" );
String url = "http://weather.yahooapis.com/forecastrss?p="
+ zipcode;
URLConnection conn = new URL(url).openConnection();
return conn.getInputStream();
}
}
This simple class opens a URLConnection to the Yahoo Weather API
and returns an InputStream. To create something to parse this feed,
we’ll need to create the YahooParser.java file in the same
directory.
package org.sonatype.mavenbook.weather;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import org.apache.log4j.Logger;
import org.dom4j.Document;
import org.dom4j.DocumentFactory;
import org.dom4j.io.SAXReader;
public class YahooParser {
private static Logger log = Logger.getLogger(YahooParser.class);
public Weather parse(InputStream inputStream) throws Exception {
Weather weather = new Weather();
log.info( "Creating XML Reader" );
SAXReader xmlReader = createXmlReader();
Document doc = xmlReader.read( inputStream );
log.info( "Parsing XML Response" );
weather.setCity(
doc.valueOf("/rss/channel/y:location/@city") );
weather.setRegion(
doc.valueOf("/rss/channel/y:location/@region") );
weather.setCountry(
doc.valueOf("/rss/channel/y:location/@country") );
weather.setCondition(
doc.valueOf("/rss/channel/item/y:condition/@text") );
weather.setTemp(
doc.valueOf("/rss/channel/item/y:condition/@temp") );
weather.setChill(
doc.valueOf("/rss/channel/y:wind/@chill") );
weather.setHumidity(
doc.valueOf("/rss/channel/y:atmosphere/@humidity") );
return weather;
}
private SAXReader createXmlReader() {
Map<String,String> uris = new HashMap<String,String>();
uris.put( "y", "http://xml.weather.yahoo.com/ns/rss/1.0" );
DocumentFactory factory = new DocumentFactory();
factory.setXPathNamespaceURIs( uris );
SAXReader xmlReader = new SAXReader();
xmlReader.setDocumentFactory( factory );
return xmlReader;
}
}
The YahooParser is the most complex class in this example. We’re not going to dive into the details of Dom4J or Jaxen here, but the class deserves some explanation. YahooParser's parse() method takes an InputStream and returns a Weather object. To do this, it needs to parse an XML document with Dom4J. Since we’re interested in elements under the Yahoo Weather XML namespace, we need to create a namespace-aware SAXReader in the createXmlReader() method. Once we create this reader and parse the document, we get an org.dom4j.Document object back. Instead of iterating through child elements, we simply address each piece of information we need using an XPath expression. Dom4J provides the XML parsing in this example, and Jaxen provides the XPath capabilities.
Once we’ve created a Weather object, we need to format our output
for human consumption. Create a file named WeatherFormatter.java in
the same directory as the other classes.
package org.sonatype.mavenbook.weather;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringWriter;
import org.apache.log4j.Logger;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;
public class WeatherFormatter {
private static Logger log = Logger.getLogger(WeatherFormatter.class);
public String format( Weather weather ) throws Exception {
log.info( "Formatting Weather Data" );
Reader reader =
new InputStreamReader( getClass().getClassLoader()
.getResourceAsStream("output.vm"));
VelocityContext context = new VelocityContext();
context.put("weather", weather );
StringWriter writer = new StringWriter();
Velocity.evaluate(context, writer, "", reader);
return writer.toString();
}
}
The WeatherFormatter uses Velocity to render a template. The
format() method takes a Weather bean and spits out a formatted
String. The first thing the format() method does is load a
Velocity template from the classpath named output.vm. We then create
a VelocityContext which is populated with a single Weather object
named weather. A StringWriter is created to hold the results of
the template merge. The template is evaluated with a call to
Velocity.evaluate() and the results are returned as a String.
Before we can run this example, we’ll need to add some resources to our classpath.
This project depends on two classpath resources: the Main class that
configures Log4J with a classpath resource named log4j.properties,
and the WeatherFormatter that references a Velocity template from
the classpath named output.vm. Both of these resources need to be in
the default package (or the root of the classpath).
To add these resources, we’ll need to create a new directory from the
base directory of the project: src/main/resources. Since this
directory was not created by the archetype:generate task, we need to
create it by executing the following commands from the project’s base
directory:
$ cd src/main $ mkdir resources $ cd resources
Once the resources directory is created, we can add the two
resources. First, add the log4j.properties file in the resources
directory, as shown in Simple Weather’s Log4J Configuration File.
# Set root category priority to INFO and its only appender to CONSOLE.
log4j.rootCategory=INFO, CONSOLE
# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Threshold=INFO
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%-4r %-5p %c{1} %x - %m%n
This log4j.properties file simply configures Log4J to print all log
messages to standard output using a PatternLayout. Lastly, we need
to create the output.vm, which is the Velocity template used to
render the output of this command-line program. Create output.vm in
the resources directory.
*********************************
Current Weather Conditions for:
${weather.city}, ${weather.region}, ${weather.country}
Temperature: ${weather.temp}
Condition: ${weather.condition}
Humidity: ${weather.humidity}
Wind Chill: ${weather.chill}
*********************************
This template contains a number of references to a variable named
weather, which is the Weather bean that was passed to the
WeatherFormatter. The ${weather.temp} syntax is shorthand
for retrieving and displaying the value of the temp bean
property. Now that we have all of our project’s code in the right
place, we can use Maven to run the example.
Using the Exec plugin from the Codehaus Mojo project, we can run the Main class:
$ mvn install $ mvn exec:java -Dexec.mainClass=org.sonatype.mavenbook.weather.Main ... [INFO] [exec:java] 0INFO YahooRetriever - Retrieving Weather Data 134 INFO YahooParser - Creating XML Reader 333 INFO YahooParser - Parsing XML Response 420 INFO WeatherFormatter - Formatting Weather Data ********************************* Current Weather Conditions for: Evanston, IL, US Temperature: 45 Condition: Cloudy Humidity: 76 Wind Chill: 38 ********************************* ...
We didn’t supply a command-line argument to the Main class, so we ended up with the default zip code, 60202. To supply a zip code, we would use the -Dexec.args argument and pass in a zip code:
$ mvn exec:java -Dexec.mainClass=org.sonatype.mavenbook.weather.Main \
-Dexec.args="70112"
...
[INFO] [exec:java]
0 INFO YahooRetriever - Retrieving Weather Data
134 INFO YahooParser - Creating XML Reader
333 INFO YahooParser - Parsing XML Response
420 INFO WeatherFormatter - Formatting Weather Data
*********************************
Current Weather Conditions for:
New Orleans, LA, US
Temperature: 82
Condition: Fair
Humidity: 71
Wind Chill: 82
*********************************
[INFO] Finished at: Sun Aug 31 09:33:34 CDT 2008
...
As you can see, we’ve successfully executed the Simple Weather
command-line tool, retrieved some data from Yahoo Weather, parsed the
result, and formatted the resulting data with Velocity. We achieved
all of this without doing much more than writing our project’s source
code and adding some minimal configuration to the pom.xml. Notice
that no “build process” was involved. We didn’t need to define how or
where the Java compiler compiles our source to bytecode, and we didn’t
need to instruct the build system how to locate the bytecode when we
executed the example application. All we needed to do to include a few
dependencies was locate the appropriate Maven coordinates.
The Exec plugin allows you to execute Java classes and other scripts. It is not a core Maven plugin, but it is available from the Mojo project hosted by Codehaus. For a full description of the Exec plugin, run:
$ mvn help:describe -Dplugin=exec -Dfull
This will list all of the goals that are available in the Maven Exec plugin. The Help plugin will also list all of the valid parameters for the Exec plugin. If you would like to customize the behavior of the Exec plugin you should use the documentation provided by help:describe as a guide. Although the Exec plugin is useful, you shouldn’t rely on it as a way to execute your application outside of running tests during development. For a more robust solution, use the Maven Assembly plugin that is demonstrated in the section Building a Packaged Command Line Application, later in this chapter.
The Exec plugin makes it possible for us to run the Simple Weather
program without having to load the appropriate dependencies into the
classpath. In any other build system, we would have to copy all of the
program dependencies into some sort of lib/ directory containing a
collection of JAR files. Then, we would have to write a simple script
that includes our program’s bytecode and all of our dependencies in a
classpath. Only then could we run java
org.sonatype.mavenbook.weather.Main. The Exec plugin leverages the
fact that Maven already knows how to create and manage your classpath
and dependencies.
This is convenient, but it’s also nice to know exactly what is being included in your project’s classpath. Although the project depends on a few libraries such as Dom4J, Log4J, Jaxen, and Velocity, it also relies on a few transitive dependencies. If you need to find out what is on the classpath, you can use the Maven Dependency plugin to print out a list of dependencies.
$ mvn dependency:resolve ... [INFO] [dependency:resolve] [INFO] [INFO] The following files have been resolved: [INFO]com.ibm.icu:icu4j:jar:2.6.1 (scope = compile) [INFO]commons-collections:commons-collections:jar:3.1 (scope = compile) [INFO]commons-lang:commons-lang:jar:2.1 (scope = compile) [INFO]dom4j:dom4j:jar:1.6.1 (scope = compile) [INFO]jaxen:jaxen:jar:1.1.1 (scope = compile) [INFO]jdom:jdom:jar:1.0 (scope = compile) [INFO]junit:junit:jar:3.8.1 (scope = test) [INFO]log4j:log4j:jar:1.2.14 (scope = compile) [INFO]oro:oro:jar:2.0.8 (scope = compile) [INFO]velocity:velocity:jar:1.5 (scope = compile) [INFO]xalan:xalan:jar:2.6.0 (scope = compile) [INFO]xerces:xercesImpl:jar:2.6.2 (scope = compile) [INFO]xerces:xmlParserAPIs:jar:2.6.2 (scope = compile) [INFO]xml-apis:xml-apis:jar:1.0.b2 (scope = compile) [INFO]xom:xom:jar:1.0 (scope = compile)
As you can see, our project has a very large set of dependencies. While we only included direct dependencies on four libraries, we appear to be depending on 15 dependencies in total. Dom4J depends on Xerces and the XML Parser APIs, and Jaxen depends on Xalan. The Dependency plugin is going to print out the final combination of dependencies under which your project is being compiled. If you would like to know about the entire dependency tree of your project, you can run the dependency:tree goal.
$ mvn dependency:tree ... [INFO] [dependency:tree] [INFO] org.sonatype.mavenbook.custom:simple-weather:jar:1.0 [INFO] +- log4j:log4j:jar:1.2.14:compile [INFO] +- dom4j:dom4j:jar:1.6.1:compile [INFO] | \- xml-apis:xml-apis:jar:1.0.b2:compile [INFO] +- jaxen:jaxen:jar:1.1.1:compile [INFO] | +- jdom:jdom:jar:1.0:compile [INFO] | +- xerces:xercesImpl:jar:2.6.2:compile [INFO] | \- xom:xom:jar:1.0:compile [INFO] | +- xerces:xmlParserAPIs:jar:2.6.2:compile [INFO] | +- xalan:xalan:jar:2.6.0:compile [INFO] | \- com.ibm.icu:icu4j:jar:2.6.1:compile [INFO] +- velocity:velocity:jar:1.5:compile [INFO] | +- commons-collections:commons-collections:jar:3.1:compile [INFO] | +- commons-lang:commons-lang:jar:2.1:compile [INFO] | \- oro:oro:jar:2.0.8:compile [INFO] +- org.apache.commons:commons-io:jar:1.3.2:test [INFO] \- junit:junit:jar:3.8.1:test ...
If you’re truly adventurous or want to see the full dependency trail,
including artifacts that were rejected due to conflicts and other
reasons, run Maven with the -X debug flag.
$ mvn install -X ... [DEBUG] org.sonatype.mavenbook.custom:simple-weather:jar:1.0 (selected for null) [DEBUG] log4j:log4j:jar:1.2.14:compile (selected for compile) [DEBUG] dom4j:dom4j:jar:1.6.1:compile (selected for compile) [DEBUG] xml-apis:xml-apis:jar:1.0.b2:compile (selected for compile) [DEBUG] jaxen:jaxen:jar:1.1.1:compile (selected for compile) [DEBUG] jaxen:jaxen:jar:1.1-beta-6:compile (removed - ) [DEBUG] jaxen:jaxen:jar:1.0-FCS:compile (removed - ) [DEBUG] jdom:jdom:jar:1.0:compile (selected for compile) [DEBUG] xml-apis:xml-apis:jar:1.3.02:compile (removed - nearer: 1.0.b2) [DEBUG] xerces:xercesImpl:jar:2.6.2:compile (selected for compile) [DEBUG] xom:xom:jar:1.0:compile (selected for compile) [DEBUG] xerces:xmlParserAPIs:jar:2.6.2:compile (selected for compile) [DEBUG] xalan:xalan:jar:2.6.0:compile (selected for compile) [DEBUG] xml-apis:xml-apis:1.0.b2. [DEBUG] com.ibm.icu:icu4j:jar:2.6.1:compile (selected for compile) [DEBUG] velocity:velocity:jar:1.5:compile (selected for compile) [DEBUG] commons-collections:commons-collections:jar:3.1:compile [DEBUG] commons-lang:commons-lang:jar:2.1:compile (selected for compile) [DEBUG] oro:oro:jar:2.0.8:compile (selected for compile) [DEBUG] junit:junit:jar:3.8.1:test (selected for test)
In the debug output, we see some of the guts of the dependency management system at work. What you see here is the tree of dependencies for this project. Maven is printing out the full Maven coordinates for all of your project’s dependencies and the mechanism at work.
Maven has built-in support for unit tests, and testing is a part of
the default Maven lifecycle. Let’s add some unit tests to our simple
weather project. First, let’s create the
org.sonatype.mavenbook.weather package under src/test/java:
$ cd src/test/java $ cd org/sonatype/mavenbook $ mkdir -p weather/yahoo $ cd weather/yahoo
At this point, we will create two unit tests. The first will test the
YahooParser, and the second will test the WeatherFormatter. In the
weather package, create a file named YahooParserTest.java with the
contents shown in the next example.
package org.sonatype.mavenbook.weather.yahoo;
import java.io.InputStream;
import junit.framework.TestCase;
import org.sonatype.mavenbook.weather.Weather;
import org.sonatype.mavenbook.weather.YahooParser;
public class YahooParserTest extends TestCase {
public YahooParserTest(String name) {
super(name);
}
public void testParser() throws Exception {
InputStream nyData = getClass().getClassLoader()
.getResourceAsStream("ny-weather.xml");
Weather weather = new YahooParser().parse( nyData );
assertEquals( "New York", weather.getCity() );
assertEquals( "NY", weather.getRegion() );
assertEquals( "US", weather.getCountry() );
assertEquals( "39", weather.getTemp() );
assertEquals( "Fair", weather.getCondition() );
assertEquals( "39", weather.getChill() );
assertEquals( "67", weather.getHumidity() );
}
}
This YahooParserTest extends the TestCase class defined by
JUnit. It follows the usual pattern for a JUnit test: a constructor
that takes a single String argument that calls the constructor of
the superclass, and a series of public methods that begin with
“test” that are invoked as unit tests. We define a single test
method, testParser, which tests the YahooParser by parsing an XML
document with known values. The test XML document is named
ny-weather.xml and is loaded from the classpath. We’ll add test
resources in Adding Unit Test Resources. In our Maven
project’s directory layout, the ny-weather.xml file is found in the
directory that contains test
resources — ${basedir}/src/test/resources under org/sonatype/mavenbook/weather/yahoo/ny-weather.xml. The file is read
as an InputStream and passed to the parse() method on
YahooParser. The parse() method returns a Weather object, which
is then tested with a series of calls to assertEquals(), a method
defined by TestCase.
In the same directory, create a file named
WeatherFormatterTest.java.
package org.sonatype.mavenbook.weather.yahoo;
import java.io.InputStream;
import org.apache.commons.io.IOUtils;
import org.sonatype.mavenbook.weather.Weather;
import org.sonatype.mavenbook.weather.WeatherFormatter;
import org.sonatype.mavenbook.weather.YahooParser;
import junit.framework.TestCase;
public class WeatherFormatterTest extends TestCase {
public WeatherFormatterTest(String name) {
super(name);
}
public void testFormat() throws Exception {
InputStream nyData = getClass().getClassLoader()
.getResourceAsStream("ny-weather.xml");
Weather weather = new YahooParser().parse( nyData );
String formattedResult = new WeatherFormatter().format( weather );
InputStream expected = getClass().getClassLoader()
.getResourceAsStream("format-expected.dat");
assertEquals( IOUtils.toString( expected ).trim(),
formattedResult.trim() );
}
}
The second unit test in this simple project tests the
WeatherFormatter. Like the YahooParserTest, the
WeatherFormatterTest also extends JUnit’s TestCase class. The
single test function reads the same test resource from
${basedir}/src/test/resources under the
org/sonatype/mavenbook/weather/yahoo directory via this unit test’s
classpath. We’ll add test resources in
Adding Unit Test Resources. WeatherFormatterTest runs
this sample input file through the YahooParser which spits out a
Weather object, and this object is then formatted with the
WeatherFormatter. Since the WeatherFormatter prints out a
String, we need to test it against some expected input. Our expected
input has been captured in a text file named format-expected.dat
which is in the same directory as ny-weather.xml. To compare the
test’s output to the expected output, we read this expected output in
as an InputStream and use Commons IO’s IOUtils class to convert
this file to a String. This String is then compared to the test
output using assertEquals().
In WeatherFormatterTest, we used a utility from Apache Commons
IO—the IOUtils class. IOUtils provides a number of helpful static
methods that take most of the work out of input/output
operations. In this particular unit test, we used IOUtils.toString() to copy the
format-expected.dat classpath resource to a String. We could have
done this without using Commons IO, but it would have required an
extra six or seven lines of code to deal with the various
InputStreamReader and StringWriter objects. The main reason we
used Commons IO was to give us an excuse to add a test-scoped
dependency on Commons IO.
A test-scoped dependency is a dependency that is available on the classpath only during test compilation and test execution. If your project has war or ear packaging, a test-scoped dependency would not be included in the project’s output archive. To add a test-scoped dependency, add the dependency element to your project’s dependencies section, as shown in the following example:
<project>
...
<dependencies>
...
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-io</artifactId>
<version>1.3.2</version>
<scope>test</scope>
</dependency>
...
</dependencies>
</project>
After you add this dependency to the pom.xml, run mvn
dependency:resolve and you should see that commons-io is now listed
as a dependency with scope test. We need to do one more thing before
we are ready to run this project’s unit tests. We need to create the
classpath resources these unit tests depend on.
A unit test has access to a set of resources which are specific to
tests. Often you’ll store files containing expected results and files
containing dummy input in the test classpath. In this project, we’re
storing a test XML document for YahooParserTest named
ny-weather.xml and a file containing expected output from the
WeatherFormatter in format-expected.dat.
To add test resources, you’ll need to create the src/test/resources
directory. This is the default directory in which Maven looks for unit
test resources. To create this directory execute the following
commands from your project’s base directory.
$ cd src/test $ mkdir resources $ cd resources
Once you’ve create the resources directory, create a file named
format-expected.dat in the resources directory.
********************************* Current Weather Conditions for: New York, NY, US Temperature: 39 Condition: Fair Humidity: 67 Wind Chill: 39 *********************************
This file should look familiar. It is the same output that was
generated previously when you ran the Simple Weather project with the
Maven Exec plugin. The second file you’ll need to add to the resources
directory is ny-weather.xml.
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<rss version="2.0" xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">
<channel>
<title>Yahoo Weather - New York, NY</title>
<link>http://us.rd.yahoo.com/dailynews/rss/weather/New_York__NY/
</link>
<description>Yahoo Weather for New York, NY</description>
<language>en-us</language>
<lastBuildDate>Sat, 10 Nov 2007 8:51 pm EDT</lastBuildDate>
<ttl>60</ttl>
<yweather:location city="New York" region="NY" country="US" />
<yweather:units temperature="F" distance="mi" pressure="in"
speed="mph"/>
<yweather:wind chill="39" direction="0" speed="0" />
<yweather:atmosphere humidity="67" visibility="1609"
pressure="30.18" rising="1" />
<yweather:astronomy sunrise="6:36 am" sunset="4:43 pm" />
<image>
<title>Yahoo Weather</title>
<width>142</width>
<height>18</height>
<link>http://weather.yahoo.com/</link>
<url>http://l.yimg.com/us.yimg.com/i/us/nws/th/main_142b.gif</url>
</image>
<item>
<title>Conditions for New York, NY at 8:51 pm EDT</title>
<geo:lat>40.67</geo:lat>
<geo:long>-73.94</geo:long>
<link>http://us.rd.yahoo.com/dailynews/rss/weather/New_York__NY/
</link>
<pubDate>Sat, 10 Nov 2007 8:51 pm EDT</pubDate>
<yweather:condition text="Fair" code="33" temp="39"
date="Sat, 10 Nov 2007 8:51 pm EDT"/>
<description><![CDATA[
<img src="http://l.yimg.com/us.yimg.com/i/us/we/52/33.gif" /><br />
<b>Current Conditions:</b><br />
Fair, 39 F<BR /><BR />
<b>Forecast:</b><BR />
Sat - Partly Cloudy. High: 45 Low: 32<br />
Sun - Sunny. High: 50 Low: 38<br />
<br />
]]></description>
<yweather:forecast day="Sat" date="10 Nov 2007" low="32" high="45"
text="Partly Cloudy" code="29" />
<yweather:forecast day="Sun" date="11 Nov 2007" low="38" high="50"
text="Sunny" code="32" />
<guid isPermaLink="false">10002_2007_11_10_20_51_EDT</guid>
</item>
</channel>
</rss>
This file contains a test XML document for the YahooParserTest. We store this file so that we can test the YahooParser without having to retrieve an XML response from Yahoo Weather.
Now that your project has unit tests, let’s run them. You don’t have to do anything special to run a unit test; the test phase is a normal part of the Maven lifecycle. You run Maven tests whenever you run mvn package or mvn install. If you would like to run all the lifecycle phases up to and including the test phase, run mvn test:
$ mvn test ... [INFO] [surefire:test] [INFO] Surefire report directory: ~/examples/ch-custom/simple-weather/target/surefire-reports ------------------------------------------------------- T E S T S ------------------------------------------------------- Running org.sonatype.mavenbook.weather.yahoo.WeatherFormatterTest 0 INFO YahooParser - Creating XML Reader 177 INFO YahooParser - Parsing XML Response 239 INFO WeatherFormatter - Formatting Weather Data Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.547 sec Running org.sonatype.mavenbook.weather.yahoo.YahooParserTest 475 INFO YahooParser - Creating XML Reader 483 INFO YahooParser - Parsing XML Response Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.018 sec Results : Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
Executing mvn test from the command line caused Maven to execute all
lifecycle phases up to the test phase. The Maven Surefire plugin has
a test goal which is bound to the test phase. This test goal
executes all of the unit tests this project can find under
src/test/java with filenames matching /Test*.java,
/Test.java and */*TestCase.java. In the case of this project,
you can see that the Surefire plugin’s test goal executed
WeatherFormatterTest and YahooParserTest. When the Maven Surefire
plugin runs the JUnit tests, it also generates XML and text reports in
the ${basedir}/target/surefire-reports directory. If your
tests are failing, you should look in this directory for details like
stack traces and error messages generated by your unit tests.
You will often find yourself developing on a system that has failing unit tests. If you are practicing Test-Driven Development (TDD), you might use test failure as a measure of how close your project is to completeness. If you have failing unit tests, and you would still like to produce build output, you are going to have to tell Maven to ignore build failures. When Maven encounters a build failure, its default behavior is to stop the current build. To continue building a project even when the Surefire plugin encounters failed test cases, you’ll need to set the testFailureIgnore configuration property of the Surefire plugin to true.
<project>
[...]
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<configuration>
<testFailureIgnore>true</testFailureIgnore>
</configuration>
</plugin>
</plugins>
</build>
[...]
</project>
The plugin documents (http://maven.apache.org/plugins/maven-surefire-plugin/test-mojo.html) show that this parameter declares an expression:
testFailureIgnore Set this to true to ignore a failure during
testing. Its use is NOT RECOMMENDED, but quite
convenient on occasion.
* Type: boolean
* Required: No
* User Property: maven.test.failure.ignore
This property can be set from the command line using the -D parameter:
$ mvn test -Dmaven.test.failure.ignore=true
You may want to configure Maven to skip unit tests altogether. Maybe you have a very large system where the unit tests take minutes to complete and you don’t want to wait for unit tests to complete before producing output. You might be working with a legacy system that has a series of failing unit tests, and instead of fixing the unit tests, you might just want to produce a JAR. Maven provides for the ability to skip unit tests using the skip parameter of the Surefire plugin. To skip tests from the command line, simply add the maven.test.skip property to any goal:
$ mvn install -Dmaven.test.skip=true ... [INFO] [compiler:testCompile] [INFO] Not compiling test sources [INFO] [surefire:test] [INFO] Tests are skipped. ...
When the Surefire plugin reaches the test goal, it will skip the
unit tests if the maven.test.skip properties is set to
true. Another way to configure Maven to skip unit tests is to add
this configuration to your project’s pom.xml. To do this, you would
add a plugin element to your build configuration.
<project>
[...]
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<configuration>
<skip>true</skip>
</configuration>
</plugin>
</plugins>
</build>
[...]
</project>
In Running the Simple Weather Program earlier in descriptor in the Maven Assembly plugin to produce a distributable JAR file, which contains the project’s bytecode and all of the dependencies.
The Maven Assembly plugin is a plugin you can use to create arbitrary
distributions for your applications. You can use the Maven Assembly
plugin to assemble the output of your project in any format you desire
by defining a custom assembly descriptor. In a later chapter we will
show you how to create a custom assembly descriptor which produces a
more complex archive for the Simple Weather application. In this
chapter, we’re going to use the predefined jar-with-dependencies
format. To configure the Maven Assembly Plugin, we need to add the
following plugin configuration to our existing build configuration in
the pom.xml.
<project>
[...]
<build>
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</plugin>
</plugins>
</build>
[...]
</project>
Once you’ve added this configuration, you can build the assembly by running the assembly:assembly goal. In the following screen listing, the assembly:assembly goal is executed after the Maven build reaches the install lifecycle phase:
$ mvn install assembly:assembly ... [INFO] [jar:jar] [INFO] Building jar: ~/examples/ch-custom/simple-weather/target/simple-weather-1.0.jar [INFO] [assembly:assembly] [INFO] Processing DependencySet (output=) [INFO] Expanding: \ .m2/repository/dom4j/dom4j/1.6.1/dom4j-1.6.1.jar into \ /tmp/archived-file-set.1437961776.tmp [INFO] Expanding: .m2/repository/commons-lang/commons-lang/2.1/\ commons-lang-2.1.jar into /tmp/archived-file-set.305257225.tmp ... (Maven Expands all dependencies into a temporary directory) ... [INFO] Building jar: \ ~/examples/ch-custom/simple-weather/target/\ simple-weather-1.0-jar-with-dependencies.jar
Once our assembly is assembled in
target/simple-weather-1.0-jar-with-dependencies.jar, we can run
the Main class again from the command line. To run the simple
weather application’s Main class, execute the following commands
from your project’s base directory:
$ cd target
$ java -cp simple-weather-1.0-jar-with-dependencies.jar \
org.sonatype.mavenbook.weather.Main 10002
0 INFO YahooRetriever - Retrieving Weather Data
221 INFO YahooParser - Creating XML Reader
399 INFO YahooParser - Parsing XML Response
474 INFO WeatherFormatter - Formatting Weather Data
*********************************
Current Weather Conditions for:
New York, NY, US
Temperature: 44
Condition: Fair
Humidity: 40
Wind Chill: 40
*********************************
The jar-with-dependencies format creates a single JAR file that includes all of the bytecode from the simple-weather project as well as the unpacked bytecode from all of the dependencies. This somewhat unconventional format produces a 9 MiB JAR file containing approximately 5,290 classes, but it does provide for an easy distribution format for applications you’ve developed with Maven. Later in this book, we’ll show you how to create a custom assembly descriptor to produce a more standard distribution.
In Maven 1, a build was customized by stringing together a series of plugin goals. Each plugin goal had prerequisites and defined a relationship to other plugin goals. With the release of Maven 2, a lifecycle was introduced and plugin goals are now associated with a series of phases in a default Maven build lifecycle. The lifecycle provides a solid foundation that makes it easier to predict and manage the plugin goals which will be executed in a given build. In Maven 1, plugin goals related to one another directly; in Maven 2, plugin goals relate to a set of common lifecycle stages. While it is certainly valid to execute a plugin goal directly from the command line as we just demonstrated, it is more consistent with the design of Maven to configure the Assembly plugin to execute the assembly:assembly goal during a phase in the Maven lifecycle.
The following plugin configuration configures the Maven Assembly plugin to execute the attached goal during the package phase of the Maven default build lifecycle. The attached goal does the same thing as the assembly goal. To bind to assembly:attached goal to the package phase we use the executions element under plugin in the build section of the project’s POM.
<project>
[...]
<build>
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
<executions>
<execution>
<id>simple-command</id>
<phase>package</phase>
<goals>
<goal>attached</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
[...]
</project>
Once you have this configuration in your POM, all you need to do to generate the assembly is run mvn package. The execution configuration will make sure that the assembly:attached goal is executed when the Maven lifecycle transitions to the package phase of the lifecycle. The assembly will also be created if you run mvn install, as the package phase precedes the install phase in the default Maven lifecycle.