Optionally let ObjectFileWriter append to existing file instead of overwriting.

Author: blackwinter

metafacture-io/src/main/java/org/metafacture/io/ObjectFileWriter.java

@@ -46,6 +46,7 @@ public final class ObjectFileWriter<T> extends AbstractObjectWriter<T>  {
     private String path;
     private int count;
     private Writer writer;
+    private boolean appendIfFileExists;
     private boolean firstObject = true;
     private boolean closed;
 
@@ -129,11 +130,26 @@ public void closeStream() {
         }
     }
 
+    /**
+     * Controls whether to open files in append mode if they exist.
+     * <p>
+     * The default value is {@code false}.
+     * <p>
+     * This property can be changed anytime during processing. It becomes
+     * effective the next time a new output file is opened.
+     *
+     * @param appendIfFileExists true if new data should be appended,
+     *                           false to overwrite the existing file.
+     */
+    public void setAppendIfFileExists(final boolean appendIfFileExists) {
+        this.appendIfFileExists = appendIfFileExists;
+    }
+
     private void startNewFile() {
         final Matcher matcher = VAR_PATTERN.matcher(this.path);
         final String currentPath = matcher.replaceAll(String.valueOf(count));
         try {
-            final OutputStream file = new FileOutputStream(currentPath);
+            final OutputStream file = new FileOutputStream(currentPath, appendIfFileExists);
             try {
                 final OutputStream compressor = compression.createCompressor(file, currentPath);
                 try {

metafacture-io/src/test/java/org/metafacture/io/ObjectFileWriterTest.java

@@ -53,21 +53,44 @@ public final class ObjectFileWriterTest
     @Before
     public void setup() throws IOException {
         file = tempFolder.newFile();
-        writer = new ObjectFileWriter<String>(file.getAbsolutePath());
+        setWriter();
     }
 
     @Test
     public void shouldWriteUTF8EncodedOutput() throws IOException {
         assumeFalse("Default encoding is UTF-8: It is not possible to test whether " +
-                        "ObjectFileWriter sets the encoding to UTF-8 correctly.",
+                "ObjectFileWriter sets the encoding to UTF-8 correctly.",
                 StandardCharsets.UTF_8.equals(Charset.defaultCharset()));
 
         writer.process(DATA);
         writer.closeStream();
 
-        final byte[] bytesWritten = Files.readAllBytes(file.toPath());
-        assertArrayEquals((DATA + "\n").getBytes(StandardCharsets.UTF_8),
-                bytesWritten); // FileObjectWriter appends new lines
+        assertOutput(DATA + "\n");
+    }
+
+    @Test
+    public void shouldOverwriteExistingFileByDefault() throws IOException {
+        writer.process(DATA);
+        writer.closeStream();
+
+        setWriter();
+        writer.process(DATA);
+        writer.closeStream();
+
+        assertOutput(DATA + "\n");
+    }
+
+    @Test
+    public void shouldAppendToExistingFile() throws IOException {
+        writer.process(DATA);
+        writer.closeStream();
+
+        setWriter();
+        writer.setAppendIfFileExists(true);
+        writer.process(DATA);
+        writer.closeStream();
+
+        assertOutput(DATA + "\n" + DATA + "\n");
     }
 
     @Override
@@ -83,4 +106,14 @@ protected String getOutput() throws IOException {
         }
     }
 
+    private void setWriter() {
+        writer = new ObjectFileWriter<String>(file.getAbsolutePath());
+    }
+
+    private void assertOutput(final String expected) throws IOException {
+        final byte[] bytesWritten = Files.readAllBytes(file.toPath());
+        assertArrayEquals(expected.getBytes(StandardCharsets.UTF_8),
+                bytesWritten); // FileObjectWriter appends new lines
+    }
+
 }