Added TaggedWriter, ClosedWriter and BrokenWriter. (#86)

Author: robtimus

src/main/java/org/apache/commons/io/output/BrokenWriter.java

@@ -0,0 +1,87 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      http://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.apache.commons.io.output;
+
+import java.io.IOException;
+import java.io.Writer;
+
+/**
+ * Broken writer. This writer always throws an {@link IOException} from
+ * all {@link Writer} methods.
+ * <p>
+ * This class is mostly useful for testing error handling in code that uses a
+ * writer.
+ *
+ * @since 2.0
+ */
+public class BrokenWriter extends Writer {
+
+    /**
+     * The exception that is thrown by all methods of this class.
+     */
+    private final IOException exception;
+
+    /**
+     * Creates a new writer that always throws the given exception.
+     *
+     * @param exception the exception to be thrown
+     */
+    public BrokenWriter(final IOException exception) {
+        this.exception = exception;
+    }
+
+    /**
+     * Creates a new writer that always throws an {@link IOException}
+     */
+    public BrokenWriter() {
+        this(new IOException("Broken writer"));
+    }
+
+    /**
+     * Throws the configured exception.
+     *
+     * @param cbuf ignored
+     * @param off ignored
+     * @param len ignored
+     * @throws IOException always thrown
+     */
+    @Override
+    public void write(final char[] cbuf, final int off, final int len) throws IOException {
+        throw exception;
+    }
+
+    /**
+     * Throws the configured exception.
+     *
+     * @throws IOException always thrown
+     */
+    @Override
+    public void flush() throws IOException {
+        throw exception;
+    }
+
+    /**
+     * Throws the configured exception.
+     *
+     * @throws IOException always thrown
+     */
+    @Override
+    public void close() throws IOException {
+        throw exception;
+    }
+
+}

src/main/java/org/apache/commons/io/output/ClosedWriter.java

@@ -0,0 +1,65 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      http://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.apache.commons.io.output;
+
+import java.io.IOException;
+import java.io.Writer;
+
+/**
+ * Closed writer. This writer throws an exception on all attempts to
+ * write something to it.
+ * <p>
+ * Typically uses of this class include testing for corner cases in methods
+ * that accept a writer and acting as a sentinel value instead of
+ * a {@code null} writer.
+ *
+ * @since 2.7
+ */
+public class ClosedWriter extends Writer {
+
+    /**
+     * A singleton.
+     */
+    public static final ClosedWriter CLOSED_WRITER = new ClosedWriter();
+
+    /**
+     * Throws an {@link IOException} to indicate that the writer is closed.
+     *
+     * @param cbuf ignored
+     * @param off ignored
+     * @param len ignored
+     * @throws IOException always thrown
+     */
+    @Override
+    public void write(final char[] cbuf, final int off, final int len) throws IOException {
+        throw new IOException("write(" + new String(cbuf) + ", " + off + ", " + len + ") failed: stream is closed");
+    }
+
+    /**
+     * Throws an {@link IOException} to indicate that the stream is closed.
+     *
+     * @throws IOException always thrown
+     */
+    @Override
+    public void flush() throws IOException {
+        throw new IOException("flush() failed: stream is closed");
+    }
+
+    @Override
+    public void close() throws IOException {
+    }
+}

src/main/java/org/apache/commons/io/output/TaggedWriter.java

@@ -0,0 +1,116 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      http://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.apache.commons.io.output;
+
+import java.io.IOException;
+import java.io.Serializable;
+import java.io.Writer;
+import java.util.UUID;
+
+import org.apache.commons.io.TaggedIOException;
+
+/**
+ * A writer decorator that tags potential exceptions so that the
+ * reader that caused the exception can easily be identified. This is
+ * done by using the {@link TaggedIOException} class to wrap all thrown
+ * {@link IOException}s. See below for an example of using this class.
+ * <pre>
+ * TaggedReader reader = new TaggedReader(...);
+ * try {
+ *     // Processing that may throw an IOException either from this reader
+ *     // or from some other IO activity like temporary files, etc.
+ *     writeToWriter(writer);
+ * } catch (IOException e) {
+ *     if (writer.isCauseOf(e)) {
+ *         // The exception was caused by this writer.
+ *         // Use e.getCause() to get the original exception.
+ *     } else {
+ *         // The exception was caused by something else.
+ *     }
+ * }
+ * </pre>
+ * <p>
+ * Alternatively, the {@link #throwIfCauseOf(Exception)} method can be
+ * used to let higher levels of code handle the exception caused by this
+ * writer while other processing errors are being taken care of at this
+ * lower level.
+ * <pre>
+ * TaggedWriter writer = new TaggedWriter(...);
+ * try {
+ *     writeToWriter(writer);
+ * } catch (IOException e) {
+ *     writer.throwIfCauseOf(e);
+ *     // ... or process the exception that was caused by something else
+ * }
+ * </pre>
+ *
+ * @see TaggedIOException
+ * @since 2.0
+ */
+public class TaggedWriter extends ProxyWriter {
+
+    /**
+     * The unique tag associated with exceptions from writer.
+     */
+    private final Serializable tag = UUID.randomUUID();
+
+    /**
+     * Creates a tagging decorator for the given writer.
+     *
+     * @param proxy writer to be decorated
+     */
+    public TaggedWriter(final Writer proxy) {
+        super(proxy);
+    }
+
+    /**
+     * Tests if the given exception was caused by this writer.
+     *
+     * @param exception an exception
+     * @return {@code true} if the exception was thrown by this writer,
+     *         {@code false} otherwise
+     */
+    public boolean isCauseOf(final Exception exception) {
+        return TaggedIOException.isTaggedWith(exception, tag);
+    }
+
+    /**
+     * Re-throws the original exception thrown by this writer. This method
+     * first checks whether the given exception is a {@link TaggedIOException}
+     * wrapper created by this decorator, and then unwraps and throws the
+     * original wrapped exception. Returns normally if the exception was
+     * not thrown by this writer.
+     *
+     * @param exception an exception
+     * @throws IOException original exception, if any, thrown by this writer
+     */
+    public void throwIfCauseOf(final Exception exception) throws IOException {
+        TaggedIOException.throwCauseIfTaggedWith(exception, tag);
+    }
+
+    /**
+     * Tags any IOExceptions thrown, wrapping and re-throwing.
+     *
+     * @param e The IOException thrown
+     * @throws IOException if an I/O error occurs
+     */
+    @Override
+    protected void handleIOException(final IOException e) throws IOException {
+        throw new TaggedIOException(e, tag);
+    }
+
+}

src/test/java/org/apache/commons/io/output/BrokenWriterTest.java

@@ -0,0 +1,87 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      http://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.apache.commons.io.output;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+import java.io.IOException;
+import java.io.Writer;
+
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * JUnit Test Case for {@link BrokenWriter}.
+ */
+public class BrokenWriterTest {
+
+    private IOException exception;
+
+    private Writer writer;
+
+    @Before
+    public void setUp() {
+        exception = new IOException("test exception");
+        writer = new BrokenWriter(exception);
+    }
+
+    @Test
+    public void testWrite() {
+        try {
+            writer.write(1);
+            fail("Expected exception not thrown.");
+        } catch (final IOException e) {
+            assertEquals(exception, e);
+        }
+
+        try {
+            writer.write(new char[1]);
+            fail("Expected exception not thrown.");
+        } catch (final IOException e) {
+            assertEquals(exception, e);
+        }
+
+        try {
+            writer.write(new char[1], 0, 1);
+            fail("Expected exception not thrown.");
+        } catch (final IOException e) {
+            assertEquals(exception, e);
+        }
+    }
+
+    @Test
+    public void testFlush() {
+        try {
+            writer.flush();
+            fail("Expected exception not thrown.");
+        } catch (final IOException e) {
+            assertEquals(exception, e);
+        }
+    }
+
+    @Test
+    public void testClose() {
+        try {
+            writer.close();
+            fail("Expected exception not thrown.");
+        } catch (final IOException e) {
+            assertEquals(exception, e);
+        }
+    }
+
+}