DynamicPackageOutputManager and its implementation (#266)

* MultiPackageOutputManager and its implementation

* header fix

* checkstyle

* code style fix

* Class rename and correct implementation of the contract.

* formatting

* Renamed interface to DynamicPackageOutputManger

* don't use Override

agrona/src/main/java/org/agrona/generation/DynamicPackageOutputManger.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2014-2022 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.generation;
+
+/**
+ * Extended version of the OutputManager allowing to specify packages for selected outputs.
+ */
+public interface DynamicPackageOutputManger extends OutputManager
+{
+    /**
+     * Sets the package name to be used by the Writer obtained through the very next call to {@link
+     * #createOutput(java.lang.String) }. A subsequent call to
+     * {@link #createOutput(java.lang.String) } should use the default package name,
+     * whatever that is.
+     *
+     * @param packageName the packageName
+     */
+    void setPackageName(String packageName);
+}

agrona/src/main/java/org/agrona/generation/StringWriterOutputManager.java

@@ -15,6 +15,8 @@
  */
 package org.agrona.generation;
 
+import java.io.FilterWriter;
+import java.io.IOException;
 import java.io.StringWriter;
 import java.io.Writer;
 import java.util.HashMap;
@@ -23,9 +25,10 @@
 /**
  * An {@link OutputManager} which can store source files as {@link StringWriter} buy source file name.
  */
-public class StringWriterOutputManager implements OutputManager
+public class StringWriterOutputManager implements DynamicPackageOutputManger
 {
     private String packageName;
+    private String basePackageName;
     private final HashMap<String, StringWriter> sourceFileByName = new HashMap<>();
 
     /**
@@ -36,7 +39,14 @@ public Writer createOutput(final String name)
         final StringWriter stringWriter = new StringWriter();
         sourceFileByName.put(packageName + "." + name, stringWriter);
 
-        return stringWriter;
+        return new FilterWriter(stringWriter)
+        {
+            public void close() throws IOException
+            {
+                super.close();
+                packageName = basePackageName;
+            }
+        };
     }
 
     /**
@@ -47,6 +57,10 @@ public Writer createOutput(final String name)
     public void setPackageName(final String packageName)
     {
         this.packageName = packageName;
+        if (basePackageName == null)
+        {
+            basePackageName = packageName;
+        }
     }
 
     /**