Add Java Example (#149)

Add a Java CDK app example to demonstrate how CDK can be used from Java.

The example demonstrates:

* Configuration of `cdk.json` to allow idiomatic use of the toolkit (`cdk synth`, `cdk deploy`).
* How to write a CDK app, stack, etc.
* How to write a reusable construct (`SinkQueue`) along with unit tests

See README file for more details.

Misc:

* Reorganize `examples/` directory to `cdk-examples-java` and `cdk-examples-typescript`

examples/cdk-examples-java/.gitignore

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+!*.t.js

examples/cdk-examples-java/README.md

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+# CDK Java Example
+
+This an example of a CDK program written in Java.
+
+> NOTE: Since this example currently resides inside the CDK repository, it takes
+  a dependency on the CDK for Java maven package that's built under
+  `packages/aws-cdk-java`. To enable this, we generate the `pom.xml` file, so we
+  can plug in the locations of the local maven repositories. This is not
+  something you will need to do if you are simply using the published CDK maven
+  package.
+
+## Building
+
+To build this app, run `npm run prepare`. This will:
+
+1. Generate `project/pom.xml` with correct references to jsii and CDK
+   dependencies.
+2. Run `mvn package`, which will compile, test and assemble an executable jar.
+
+## IDE
+
+Once the `pom.xml` file is generated, the [`./project`](./project) directory is
+fully functional Maven project, and you should be able to open it from any Java
+IDE which supports Maven.
+
+You can use the IDE to write code and unit tests, but you will need to use the
+CDK toolkit if you wish to synthesize/deploy stacks.
+
+## CDK Toolkit
+
+The [`cdk.json`](./cdk.json) file in the root of this repository includes
+instructions for the CDK toolkit on how to execute this program. Specifically,
+it will use `java -jar <executale-jar> app` for the `--app` switch. This means,
+you should be able to use the toolkit normally:
+
+```
+$ cdk ls
+<list all stacks in this program>
+
+$ cdk synth
+<cloudformation template>
+
+$ cdk deploy
+<deploy stack to your account>
+
+$ cdk diff
+<diff against deployed stack>
+```
+
+If you make modifications, make sure to rebuild the app, either by callign `mvn
+package` from `./project` or `npm run prepare` from the root.

examples/cdk-examples-java/cdk.json

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+{
+  "app": "java -jar project/target/cdk-examples-java-0.7.2-beta-jar-with-dependencies.jar app"
+}

examples/cdk-examples-java/generate.sh

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+#!/bin/bash
+set -euo pipefail
+node ./pom.xml.t.js > project/pom.xml

examples/cdk-examples-java/package.json

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+{
+  "name": "cdk-examples-java",
+  "version": "0.7.2-beta",
+  "description": "CDK examples in Java",
+  "private": true,
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/awslabs/aws-cdk"
+  },
+  "pkglint": {
+    "ignore": true
+  },
+  "scripts": {
+    "prepare": "/bin/bash generate.sh && cd project && mvn package",
+    "cdk": "cdk",
+    "test": "echo ok"
+  },
+  "author": {
+    "name": "Amazon Web Services",
+    "url": "https://aws.amazon.com"
+  },
+  "license": "Apache-2.0",
+  "dependencies": {
+    "aws-cdk-java": "^0.7.2-beta"
+  },
+  "devDependencies": {
+    "aws-cdk": "^0.7.2-beta",
+    "pkgtools": "^0.7.2-beta"
+  }
+}

examples/cdk-examples-java/pom.xml.t.js

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+const path = require('path');
+const version = require('./package.json').version;
+
+const mavenFromNpm = name => ({
+    version: require(`${name}/package.json`).version,
+    repo: path.join(path.dirname(require.resolve(name)), 'maven-repo'),
+});
+
+const cdk = mavenFromNpm('aws-cdk-java');
+const jsii = mavenFromNpm('jsii-java-runtime');
+
+process.stdout.write(`
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!-- Generated by ${__filename} at ${new Date().toISOString()} -->
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+    <modelVersion>4.0.0</modelVersion>
+
+    <repositories>
+        <repository>
+            <id>cdk</id>
+            <url>file://${cdk.repo}</url>
+        </repository>
+        <repository>
+            <id>jsii</id>
+            <url>file://${jsii.repo}</url>
+        </repository>
+    </repositories>
+
+    <groupId>com.amazonaws.cdk</groupId>
+    <artifactId>cdk-examples-java</artifactId>
+    <version>${version}</version>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.7.0</version>
+                <configuration>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                </configuration>
+            </plugin>
+
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <version>3.1.0</version>
+                <configuration>
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                    <archive>
+                        <manifest>
+                            <mainClass>com.amazonaws.cdk.examples.HelloJavaApp</mainClass>
+                        </manifest>
+                    </archive>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>make-assembly</id> <!-- this is used for inheritance merges -->
+                        <phase>package</phase> <!-- bind to the packaging phase -->
+                            <goals>
+                            <goal>single</goal>
+                        </goals>
+                    </execution>
+              </executions>
+            </plugin>
+
+        </plugins>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.amazonaws</groupId>
+            <artifactId>jsii-runtime</artifactId>
+            <version>${jsii.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>com.amazonaws.cdk</groupId>
+            <artifactId>aws-cdk</artifactId>
+            <version>${cdk.version}</version>
+        </dependency>
+
+        <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-core</artifactId>
+            <version>2.9.5</version>
+        </dependency>
+
+        <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>2.9.5</version>
+        </dependency>
+
+        <!-- https://mvnrepository.com/artifact/junit/junit -->
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
+
+    </dependencies>
+
+
+</project>
+`);

examples/cdk-examples-java/project/.gitignore

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+target
+
+# generated by pom.xml.t.js
+pom.xml
+
+.idea
+.classpath
+.project
+.settings

examples/cdk-examples-java/project/src/main/java/com/amazonaws/cdk/examples/HelloJavaApp.java

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+package com.amazonaws.cdk.examples;
+
+import com.amazonaws.cdk.App;
+
+import java.util.Arrays;
+
+public class HelloJavaApp {
+    public static void main(final String[] args) {
+        App app = new App(Arrays.asList(args));
+
+        new HelloJavaStack(app, "hello-cdk");
+
+        System.out.println(app.run());
+    }
+}

examples/cdk-examples-java/project/src/main/java/com/amazonaws/cdk/examples/HelloJavaStack.java

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+package com.amazonaws.cdk.examples;
+
+import com.amazonaws.cdk.App;
+import com.amazonaws.cdk.Stack;
+import com.amazonaws.cdk.StackProps;
+import com.amazonaws.cdk.Construct;
+import com.amazonaws.cdk.ec2.Fleet;
+import com.amazonaws.cdk.ec2.FleetProps;
+import com.amazonaws.cdk.ec2.InstanceType;
+import com.amazonaws.cdk.ec2.VpcNetwork;
+import com.amazonaws.cdk.ec2.WindowsImage;
+import com.amazonaws.cdk.ec2.WindowsVersion;
+import com.amazonaws.cdk.resources.s3.BucketResource;
+import com.amazonaws.cdk.resources.s3.BucketResourceProps;
+import com.amazonaws.cdk.sns.Topic;
+import com.amazonaws.cdk.sqs.Queue;
+import com.amazonaws.cdk.sqs.QueueProps;
+
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Hello, CDK for Java!
+ */
+class HelloJavaStack extends Stack {
+    public HelloJavaStack(final App parent, final String name) {
+        super(parent, name);
+
+        VpcNetwork vpc = new VpcNetwork(this, "VPC");
+
+        MyFleetProps fleetProps = new MyFleetProps();
+        fleetProps.vpc = vpc;
+
+        int topicCount = 5;
+
+        SinkQueue sinkQueue = new SinkQueue(this, "MySinkQueue", SinkQueueProps.builder().withRequiredTopicCount(5).build());
+
+        for (int i = 0; i < topicCount; ++i) {
+            sinkQueue.subscribe(new Topic(this, "Topic" + (i+1)));
+        }
+
+        new MyFleet(this, "MyFleet", fleetProps);
+    }
+
+    static class MyFleetProps {
+        public VpcNetwork vpc;
+    }
+
+    static class MyFleet extends Construct {
+        MyFleet(final Construct parent, final String name, final MyFleetProps props) {
+            super(parent, name);
+
+            new Fleet(this, "Compute", FleetProps.builder()
+                .withInstanceType(new InstanceType("t2.micro"))
+                .withMachineImage(new WindowsImage(WindowsVersion.WindowsServer2016EnglishNanoBase))
+                .withVpc(props.vpc)
+                .build());
+        }
+
+        @Override
+        public List<String> validate() {
+            System.err.println("Validating MyFleet...");
+            return Collections.emptyList();
+        }
+    }
+}

examples/cdk-examples-java/project/src/main/java/com/amazonaws/cdk/examples/SinkQueue.java

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+package com.amazonaws.cdk.examples;
+
+import com.amazonaws.cdk.Construct;
+import com.amazonaws.cdk.sns.Topic;
+import com.amazonaws.cdk.sqs.Queue;
+import com.amazonaws.cdk.sqs.QueueProps;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * A sink queue is a queue aggregates messages published to any number of SNS topics.
+ */
+public class SinkQueue extends Construct {
+    private final Queue queue;
+    private final int expectedTopicCount;
+
+    private int actualTopicCount = 0;
+
+    /**
+     * Defines a SinkQueue.
+     *
+     * @param parent Parent construct
+     * @param name   Logical name
+     * @param props  Props
+     */
+    public SinkQueue(final Construct parent, final String name, SinkQueueProps props) {
+        super(parent, name);
+
+        // ensure props is non-null
+        props = props != null ? props : SinkQueueProps.builder().build();
+
+        // defaults
+        QueueProps queueProps = props.getQueueProps();
+        this.expectedTopicCount = props.getRequiredTopicCount() != null ? props.getRequiredTopicCount().intValue() : 10;
+
+        // WORKAROUND: https://github.com/awslabs/aws-cdk/issues/157
+        if (queueProps == null) {
+            queueProps = QueueProps.builder().build();
+        }
+
+        this.queue = new Queue(this, "Resource", queueProps);
+    }
+
+    /**
+     * Defines a SinkQueue with default props.
+     * @param parent Parent construct
+     * @param name   Logical name
+     */
+    public SinkQueue(final Construct parent, final String name) {
+        this(parent, name, null);
+    }
+
+    /**
+     * Subscribes this queue to receive messages published to the specified topics.
+     *
+     * @param topics The topics to subscribe to
+     */
+    public void subscribe(final Topic... topics) {
+        for (Topic topic: topics) {
+            if (actualTopicCount == expectedTopicCount) {
+                throw new RuntimeException("Cannot add more topics to the sink. Maximum topics is configured to " + this.expectedTopicCount);
+            }
+            topic.subscribeQueue(this.queue);
+            actualTopicCount++;
+        }
+    }
+
+    @Override
+    public List<String> validate() {
+        if (actualTopicCount < expectedTopicCount) {
+            return Arrays.asList(
+                "There are not enough subscribers to the sink. Expecting " +
+                    this.expectedTopicCount +
+                    ", actual is " + this.actualTopicCount);
+        }
+
+        return super.validate();
+    }
+}