Merge pull request #475 from metafacture/appendIfFileExistsInObjectFileWriter

Optionally let `ObjectFileWriter` append to existing file instead of overwriting.

Author: blackwinter

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

@@ -46,7 +46,8 @@ public final class ObjectFileWriter<T> extends AbstractObjectWriter<T>  {
     private String path;
     private int count;
     private Writer writer;
-    private boolean firstObject;
+    private boolean appendIfFileExists;
+    private boolean firstObject = true;
     private boolean closed;
 
     private String encoding = "UTF-8";
@@ -59,12 +60,6 @@ public final class ObjectFileWriter<T> extends AbstractObjectWriter<T>  {
      */
     public ObjectFileWriter(final String path) {
         this.path = path;
-        startNewFile();
-
-        final Matcher matcher = VAR_PATTERN.matcher(this.path);
-        if (!matcher.find()) {
-            this.path = this.path + VAR;
-        }
     }
 
     @Override
@@ -97,13 +92,13 @@ public void process(final T obj) {
         assert !closed;
         try {
             if (firstObject) {
-                writer.write(getHeader());
+                getWriter().write(getHeader());
                 firstObject = false;
             }
             else {
-                writer.write(getSeparator());
+                getWriter().write(getSeparator());
             }
-            writer.write(obj.toString());
+            getWriter().write(obj.toString());
         }
         catch (final IOException e) {
             throw new MetafactureException(e);
@@ -112,20 +107,7 @@ public void process(final T obj) {
 
     @Override
     public void resetStream() {
-        if (!closed) {
-            try {
-                if (!firstObject) {
-                    writer.write(getFooter());
-                }
-                writer.close();
-            }
-            catch (final IOException e) {
-                throw new MetafactureException(e);
-            }
-            finally {
-                closed = true;
-            }
-        }
+        closeStream();
         startNewFile();
         ++count;
     }
@@ -135,9 +117,9 @@ public void closeStream() {
         if (!closed) {
             try {
                 if (!firstObject) {
-                    writer.write(getFooter());
+                    getWriter().write(getFooter());
                 }
-                writer.close();
+                getWriter().close();
             }
             catch (final IOException e) {
                 throw new MetafactureException(e);
@@ -148,11 +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 {
@@ -175,4 +172,17 @@ private void startNewFile() {
         }
     }
 
+    private Writer getWriter() {
+        if (writer == null) {
+            startNewFile();
+
+            final Matcher matcher = VAR_PATTERN.matcher(this.path);
+            if (!matcher.find()) {
+                this.path = this.path + VAR;
+            }
+        }
+
+        return writer;
+    }
+
 }

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

@@ -47,6 +47,7 @@ public final class ObjectFileWriterCompressionTest {
     private static final String FILENAME_BZ2 = "compressed.txt.bz2";
     private static final String FILENAME_BZIP2 = "compressed.txt.bzip2";
     private static final String FILENAME_GZ = "compressed.txt.gz";
+    private static final String FILENAME_GZ_NOAUTO = "compressed.txt.gz.noauto";
     private static final String FILENAME_GZIP = "compressed.txt.gzip";
     private static final String FILENAME_XZ = "compressed.txt.xz";
 
@@ -76,11 +77,13 @@ public static Iterable<Object[]> data() {
                 { FILENAME_BZ2, FileCompression.AUTO, MAGIC_BYTES_BZIP2 },
                 { FILENAME_BZIP2, FileCompression.AUTO, MAGIC_BYTES_BZIP2 },
                 { FILENAME_GZ, FileCompression.AUTO, MAGIC_BYTES_GZIP },
+                { FILENAME_GZ_NOAUTO, FileCompression.AUTO, MAGIC_BYTES_NONE },
                 { FILENAME_GZIP, FileCompression.AUTO, MAGIC_BYTES_GZIP },
                 { FILENAME_XZ, FileCompression.AUTO, MAGIC_BYTES_XZ },
                 { FILENAME_NONE, FileCompression.NONE, MAGIC_BYTES_NONE },
                 { FILENAME_BZ2, FileCompression.BZIP2, MAGIC_BYTES_BZIP2 },
                 { FILENAME_GZ, FileCompression.GZIP, MAGIC_BYTES_GZIP },
+                { FILENAME_GZ_NOAUTO, FileCompression.GZIP, MAGIC_BYTES_GZIP },
                 { FILENAME_XZ, FileCompression.XZ, MAGIC_BYTES_XZ },
             });
     }

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
+    }
+
 }