Introduce UuidField parameter to inject UUID for every log message.

README.md

@@ -120,6 +120,22 @@ Because of this, when adding support for the new format, `JSONEventLayoutV1` was
 
 Work has stopped on V0 but it won't be removed. No new features are added to V0 (custom UserFields for instance).
 
+# Uuid Field
+You can add a UUID to every log message in the log4jconfig:
+
+```xml
+<layout class="net.logstash.log4j.JSONEventLayoutV1" >
+  <param name="UuidField" value="@uuid" />
+</layout>
+```
+
+or
+
+```
+log4j.appender.RollingLog.layout=net.logstash.log4j.JSONEventLayoutV1
+log4j.appender.RollingLog.layout.UuidField=@uuid
+```
+
 # Custom User Fields
 As of version 1.6, you can now add your own metadata to the event in the form of comma-separated key:value pairs. This can be set in either the log4jconfig OR set on the java command-line:
 

src/main/java/net/logstash/log4j/JSONEventLayoutV1.java

@@ -13,11 +13,13 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.TimeZone;
+import java.util.UUID;
 
 public class JSONEventLayoutV1 extends Layout {
 
     private boolean locationInfo = false;
     private String customUserFields;
+    private String uuidField;
 
     private boolean ignoreThrowable = false;
 
@@ -77,6 +79,10 @@ public String format(LoggingEvent loggingEvent) {
         logstashEvent.put("@version", version);
         logstashEvent.put("@timestamp", dateFormat(timestamp));
 
+        if (getUuidField() != null) {
+            logstashEvent.put(getUuidField(), UUID.randomUUID().toString());
+        }
+
         /**
          * Extract and add fields from log4j config, if defined
          */
@@ -162,6 +168,9 @@ public void setLocationInfo(boolean locationInfo) {
     public String getUserFields() { return customUserFields; }
     public void setUserFields(String userFields) { this.customUserFields = userFields; }
 
+    public String getUuidField() { return uuidField; }
+    public void setUuidField(String uuidField) { this.uuidField = uuidField; }
+
     public void activateOptions() {
         activeIgnoreThrowable = ignoreThrowable;
     }

src/test/java/net/logstash/log4j/JSONEventLayoutV1Test.java

@@ -125,7 +125,7 @@ public void testJSONEventLayoutUserFieldsPropOverride() {
         Assert.assertTrue("Event is not valid JSON", JSONValue.isValidJsonStrict(message));
         Object obj = JSONValue.parse(message);
         JSONObject jsonObject = (JSONObject) obj;
-        Assert.assertTrue("Event does not contain field 'field1'" , jsonObject.containsKey("field1"));
+        Assert.assertTrue("Event does not contain field 'field1'", jsonObject.containsKey("field1"));
         Assert.assertEquals("Event does not contain value 'propval1'", "propval1", jsonObject.get("field1"));
 
         layout.setUserFields(prevUserData);
@@ -291,4 +291,32 @@ public void testDateFormat() {
         long timestamp = 1364844991207L;
         Assert.assertEquals("format does not produce expected output", "2013-04-01T19:36:31.207Z", JSONEventLayoutV1.dateFormat(timestamp));
     }
+
+    @Test
+    public void testJSONEventHasUuid() throws Exception {
+        JSONEventLayoutV1 layout = (JSONEventLayoutV1) appender.getLayout();
+        layout.setUuidField("@uuid");
+
+        logger.info("this is an info message with @uuid field");
+        String message = appender.getMessages()[0];
+        Assert.assertTrue("Event is not valid JSON", JSONValue.isValidJsonStrict(message));
+        Object obj = JSONValue.parse(message);
+        JSONObject jsonObject = (JSONObject) obj;
+        Assert.assertTrue("Event does not contain field '@uuid'" , jsonObject.containsKey("@uuid"));
+        Assert.assertNotNull("Field '@uuid' is null", jsonObject.get("@uuid"));
+
+        layout.setUuidField(null);
+    }
+
+    @Test
+    public void testJSONEventHasNotUuid() throws Exception {
+        JSONEventLayoutV1 layout = (JSONEventLayoutV1) appender.getLayout();
+
+        logger.info("this is an info message w/o @uuid field");
+        String message = appender.getMessages()[0];
+        Assert.assertTrue("Event is not valid JSON", JSONValue.isValidJsonStrict(message));
+        Object obj = JSONValue.parse(message);
+        JSONObject jsonObject = (JSONObject) obj;
+        Assert.assertFalse("Event does not contain field '@uuid'" , jsonObject.containsKey("@uuid"));
+    }
 }