[Java] Provide the ability to configure what action is taken when loa…

…ding properties files. Issue #226.

agrona/src/main/java/org/agrona/PropertyAction.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2014-2020 Real Logic Limited.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.agrona;
+
+/**
+ * Action to be taken for each property loaded into system properties.
+ */
+public enum PropertyAction
+{
+    /**
+     * Replace existing property value if one exists.
+     */
+    REPLACE,
+
+    /**
+     * Preserve existing property value if one exists.
+     */
+    PRESERVE
+}

agrona/src/main/java/org/agrona/SystemUtil.java

@@ -15,9 +15,7 @@
  */
 package org.agrona;
 
-import java.io.File;
-import java.io.FileInputStream;
-import java.io.InputStream;
+import java.io.*;
 import java.lang.management.ManagementFactory;
 import java.lang.management.RuntimeMXBean;
 import java.lang.management.ThreadInfo;
@@ -193,7 +191,7 @@ public static String threadDump()
     }
 
     /**
-     * Load system properties from a given filename or url.
+     * Load system properties from a given filename or url with default to {@link PropertyAction#REPLACE}.
      * <p>
      * File is first searched for in resources using the system {@link ClassLoader},
      * then file system, then URL. All are loaded if multiples found.
@@ -202,15 +200,26 @@ public static String threadDump()
      */
     public static void loadPropertiesFile(final String filenameOrUrl)
     {
-        final Properties properties = new Properties(System.getProperties());
-        System.getProperties().forEach(properties::put);
+        loadPropertiesFile(PropertyAction.REPLACE, filenameOrUrl);
+    }
 
+    /**
+     * Load system properties from a given filename or url.
+     * <p>
+     * File is first searched for in resources using the system {@link ClassLoader},
+     * then file system, then URL. All are loaded if multiples found.
+     *
+     * @param propertyAction  to take with each loaded property.
+     * @param filenameOrUrl that holds properties.
+     */
+    public static void loadPropertiesFile(final PropertyAction propertyAction, final String filenameOrUrl)
+    {
         final URL resource = ClassLoader.getSystemClassLoader().getResource(filenameOrUrl);
         if (null != resource)
         {
             try (InputStream in = resource.openStream())
             {
-                properties.load(in);
+                loadProperties(propertyAction, in);
             }
             catch (final Exception ignore)
             {
@@ -220,9 +229,9 @@ public static void loadPropertiesFile(final String filenameOrUrl)
         final File file = new File(filenameOrUrl);
         if (file.exists())
         {
-            try (FileInputStream in = new FileInputStream(file))
+            try (InputStream in = new FileInputStream(file))
             {
-                properties.load(in);
+                loadProperties(propertyAction, in);
             }
             catch (final Exception ignore)
             {
@@ -231,26 +240,36 @@ public static void loadPropertiesFile(final String filenameOrUrl)
 
         try (InputStream in = new URL(filenameOrUrl).openStream())
         {
-            properties.load(in);
+            loadProperties(propertyAction, in);
         }
         catch (final Exception ignore)
         {
         }
+    }
 
-        System.setProperties(properties);
+    /**
+     * Load system properties from a given set of filenames or URLs with default to {@link PropertyAction#REPLACE}.
+     *
+     * @param filenamesOrUrls that holds properties.
+     * @see #loadPropertiesFile(String)
+     */
+    public static void loadPropertiesFiles(final String... filenamesOrUrls)
+    {
+        loadPropertiesFiles(PropertyAction.REPLACE, filenamesOrUrls);
     }
 
     /**
      * Load system properties from a given set of filenames or URLs.
      *
+     * @param propertyAction  to take with each loaded property.
      * @param filenamesOrUrls that holds properties.
      * @see #loadPropertiesFile(String)
      */
-    public static void loadPropertiesFiles(final String... filenamesOrUrls)
+    public static void loadPropertiesFiles(final PropertyAction propertyAction, final String... filenamesOrUrls)
     {
         for (final String filenameOrUrl : filenamesOrUrls)
         {
-            loadPropertiesFile(filenameOrUrl);
+            loadPropertiesFile(propertyAction, filenameOrUrl);
         }
     }
 
@@ -440,4 +459,30 @@ public static long parseDuration(final String propertyName, final String propert
                     propertyName + ": " + propertyValue + " should end with: s, ms, us, or ns.");
         }
     }
+
+    private static void loadProperties(final PropertyAction propertyAction, final InputStream in) throws IOException
+    {
+        final Properties systemProperties = System.getProperties();
+        final Properties properties = new Properties();
+
+        properties.load(in);
+        properties.forEach(
+            (k, v) ->
+            {
+                switch (propertyAction)
+                {
+                    case PRESERVE:
+                        if (!systemProperties.containsKey(k))
+                        {
+                            systemProperties.setProperty((String)k, (String)v);
+                        }
+                        break;
+
+                    default:
+                    case REPLACE:
+                        systemProperties.setProperty((String)k, (String)v);
+                        break;
+                }
+            });
+    }
 }

agrona/src/test/java/org/agrona/SystemUtilTest.java

@@ -21,36 +21,35 @@
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.emptyOrNullString;
 import static org.hamcrest.core.Is.is;
-import static org.junit.jupiter.api.Assertions.assertNotEquals;
-import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.*;
 
 public class SystemUtilTest
 {
     @Test
     public void shouldParseSizesWithSuffix()
     {
-        assertThat(parseSize("", "1"), is(1L));
-        assertThat(parseSize("", "1k"), is(1024L));
-        assertThat(parseSize("", "1K"), is(1024L));
-        assertThat(parseSize("", "1m"), is(1024L * 1024));
-        assertThat(parseSize("", "1M"), is(1024L * 1024));
-        assertThat(parseSize("", "1g"), is(1024L * 1024 * 1024));
-        assertThat(parseSize("", "1G"), is(1024L * 1024 * 1024));
+        assertEquals(1L, parseSize("", "1"));
+        assertEquals(1024L, parseSize("", "1k"));
+        assertEquals(1024L, parseSize("", "1K"));
+        assertEquals(1024L * 1024L, parseSize("", "1m"));
+        assertEquals(1024L * 1024L, parseSize("", "1M"));
+        assertEquals(1024L * 1024L * 1024L, parseSize("", "1g"));
+        assertEquals(1024L * 1024L * 1024L, parseSize("", "1G"));
     }
 
     @Test
     public void shouldParseTimesWithSuffix()
     {
-        assertThat(parseDuration("", "1"), is(1L));
-        assertThat(parseDuration("", "1ns"), is(1L));
-        assertThat(parseDuration("", "1NS"), is(1L));
-        assertThat(parseDuration("", "1us"), is(1000L));
-        assertThat(parseDuration("", "1US"), is(1000L));
-        assertThat(parseDuration("", "1ms"), is(1000L * 1000));
-        assertThat(parseDuration("", "1MS"), is(1000L * 1000));
-        assertThat(parseDuration("", "1s"), is(1000L * 1000 * 1000));
-        assertThat(parseDuration("", "1S"), is(1000L * 1000 * 1000));
-        assertThat(parseDuration("", "12s"), is(12L * 1000 * 1000 * 1000));
+        assertEquals(1L, parseDuration("", "1"));
+        assertEquals(1L, parseDuration("", "1ns"));
+        assertEquals(1L, parseDuration("", "1NS"));
+        assertEquals(1000L, parseDuration("", "1us"));
+        assertEquals(1000L, parseDuration("", "1US"));
+        assertEquals(1000L * 1000, parseDuration("", "1ms"));
+        assertEquals(1000L * 1000, parseDuration("", "1MS"));
+        assertEquals(1000L * 1000 * 1000, parseDuration("", "1s"));
+        assertEquals(1000L * 1000 * 1000, parseDuration("", "1S"));
+        assertEquals(12L * 1000 * 1000 * 1000, parseDuration("", "12S"));
     }
 
     @Test
@@ -78,7 +77,7 @@ public void shouldDoNothingToSystemPropsWhenLoadingFileWhichDoesNotExist()
 
         loadPropertiesFile("$unknown-file$");
 
-        assertThat(originalSystemPropSize, is(System.getProperties().size()));
+        assertEquals(originalSystemPropSize, System.getProperties().size());
     }
 
     @Test
@@ -89,19 +88,31 @@ public void shouldMergeMultiplePropFilesTogether()
 
         loadPropertiesFiles("TestFileA.properties", "TestFileB.properties");
 
-        assertThat(System.getProperty("TestFileA.foo"), is("AAA"));
-        assertThat(System.getProperty("TestFileB.foo"), is("BBB"));
+        assertEquals("AAA", System.getProperty("TestFileA.foo"));
+        assertEquals("BBB", System.getProperty("TestFileB.foo"));
     }
 
     @Test
     public void shouldOverrideSystemPropertiesWithConfigFromPropFile()
     {
         System.setProperty("TestFileA.foo", "ToBeOverridden");
-        assertThat(System.getProperty("TestFileA.foo"), is("ToBeOverridden"));
+        assertEquals("ToBeOverridden", System.getProperty("TestFileA.foo"));
 
         loadPropertiesFile("TestFileA.properties");
 
-        assertThat(System.getProperty("TestFileA.foo"), is("AAA"));
+        assertEquals("AAA", System.getProperty("TestFileA.foo"));
+
+        System.clearProperty("TestFileA.foo");
+    }
+
+    @Test
+    public void shouldNotOverrideSystemPropertiesWithConfigFromPropFile()
+    {
+        System.setProperty("TestFileA.foo", "ToBeNotOverridden");
+        assertEquals("ToBeNotOverridden", System.getProperty("TestFileA.foo"));
+
+        loadPropertiesFile(PropertyAction.PRESERVE, "TestFileA.properties");
+        assertEquals("ToBeNotOverridden", System.getProperty("TestFileA.foo"));
 
         System.clearProperty("TestFileA.foo");
     }