[IO-613] Add classes ClosedReader and CloseShieldReader. Closes #84.

Applied modified patch from Rob Spoor.

Author: Gary Gregory

src/changes/changes.xml

@@ -113,6 +113,9 @@ The <action> type attribute can be add,update,fix,remove.
       <action issue="IO-612" dev="ggregory" type="add" due-to="Rob Spoor, Gary Gregory">
         Add class TeeReader.
       </action>
+      <action issue="IO-613" dev="ggregory" type="add" due-to="Rob Spoor, Gary Gregory">
+        Add classes ClosedReader and CloseShieldReader. #84.
+      </action>
     </release>
 
     <release version="2.6" date="2017-10-15" description="Java 7 required, Java 9 supported.">

src/main/java/org/apache/commons/io/input/CloseShieldInputStream.java

@@ -24,6 +24,7 @@
  * This class is typically used in cases where an input stream needs to be
  * passed to a component that wants to explicitly close the stream even if
  * more input would still be available to other components.
+ * </p>
  *
  * @since 1.4
  */
@@ -46,7 +47,7 @@ public CloseShieldInputStream(final InputStream in) {
      */
     @Override
     public void close() {
-        in = new ClosedInputStream();
+        in = ClosedInputStream.CLOSED_INPUT_STREAM;
     }
 
 }

src/main/java/org/apache/commons/io/input/CloseShieldReader.java

@@ -0,0 +1,53 @@
+/*
+ * 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.input;
+
+import java.io.Reader;
+
+/**
+ * Proxy stream that prevents the underlying reader from being closed.
+ * <p>
+ * This class is typically used in cases where a reader needs to be
+ * passed to a component that wants to explicitly close the reader even if
+ * more input would still be available to other components.
+ * <p>
+ *
+ * @since 2.7
+ */
+public class CloseShieldReader extends ProxyReader {
+
+    /**
+     * Creates a proxy that shields the given reader from being
+     * closed.
+     *
+     * @param in underlying reader
+     */
+    public CloseShieldReader(final Reader in) {
+        super(in);
+    }
+
+    /**
+     * Replaces the underlying reader with a {@link ClosedReader}
+     * sentinel. The original reader will remain open, but this proxy
+     * will appear closed.
+     */
+    @Override
+    public void close() {
+        in = ClosedReader.CLOSED_READER;
+    }
+
+}

src/main/java/org/apache/commons/io/input/ClosedReader.java

@@ -0,0 +1,60 @@
+/*
+ * 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.input;
+
+import static org.apache.commons.io.IOUtils.EOF;
+
+import java.io.IOException;
+import java.io.Reader;
+
+/**
+ * Closed reader. This reader returns EOF to all attempts to read
+ * something from it.
+ * <p>
+ * Typically uses of this class include testing for corner cases in methods
+ * that accept readers and acting as a sentinel value instead of a
+ * {@code null} reader.
+ * </p>
+ *
+ * @since 2.7
+ */
+public class ClosedReader extends Reader {
+
+    /**
+     * A singleton.
+     */
+    public static final ClosedReader CLOSED_READER = new ClosedReader();
+
+    /**
+     * Returns -1 to indicate that the stream is closed.
+     *
+     * @param cbuf ignored
+     * @param off ignored
+     * @param len ignored
+     * @return always -1
+     */
+    @Override
+    public int read(final char[] cbuf, final int off, final int len) {
+        return EOF;
+    }
+
+    @Override
+    public void close() throws IOException {
+        // noop
+    }
+
+}

src/test/java/org/apache/commons/io/input/CloseShieldReaderTest.java

@@ -0,0 +1,58 @@
+/*
+ * 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.input;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+
+import java.io.IOException;
+import java.io.Reader;
+
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * JUnit Test Case for {@link CloseShieldReader}.
+ */
+public class CloseShieldReaderTest {
+
+    private String data;
+
+    private Reader original;
+
+    private Reader shielded;
+
+    @Before
+    public void setUp() {
+        data = "xyz";
+        original = spy(new CharSequenceReader(data));
+        shielded = new CloseShieldReader(original);
+    }
+
+    @Test
+    public void testClose() throws IOException {
+        shielded.close();
+        verify(original, never()).close();
+        char[] cbuf = new char[10];
+        assertEquals("read(cbuf, off, len)", -1, shielded.read(cbuf, 0, 10));
+        assertEquals("read(cbuf, off, len)", data.length(), original.read(cbuf, 0, 10));
+        assertEquals(data, new String(cbuf, 0, data.length()));
+    }
+
+}

src/test/java/org/apache/commons/io/input/ClosedReaderTest.java

@@ -0,0 +1,35 @@
+/*
+ * 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.input;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+/**
+ * JUnit Test Case for {@link ClosedReader}.
+ */
+public class ClosedReaderTest {
+
+    @Test
+    public void testRead() throws Exception {
+        try (final ClosedReader cr = new ClosedReader()) {
+            assertEquals("read(cbuf, off, len)", -1, cr.read(new char[10], 0, 10));
+        }
+    }
+
+}