helper class for working with closeable resources like streams

CloseableTemplate.java

/**
 *
 * 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.camel.util;

import java.io.Closeable;
import java.io.IOException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * A helper class to help folks write some code using a closable resource
 */
public abstract class CloseableTemplate<T extends Closeable, R> {
    private static final transient Log LOG = LogFactory.getLog(CloseableTemplate.class);

    public R use(T stream) throws Exception {
        R answer;

        try {
            answer = doUse(stream);
        } catch (Exception e) {
            // lets close the stream catching and ignoring any exceptions as we are about to
            // rethrow the actual exception
            try {
                stream.close();
            } catch (IOException closeException) {
                // ignore this exception
                LOG.debug("Caught exception closing stream: " + e, e);
            }
            throw e;
        }

        // we processed correctly so lets let any close exceptions throw
        if (stream != null) {
            stream.close();
        }
        return answer;
    }

    /**
     * Actually process the stream
     */
    protected abstract R doUse(T stream) throws Exception;
}

CloseableTemplateTest.java

/**
 * 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.camel.util;

import junit.framework.Assert;
import junit.framework.TestCase;

import java.io.BufferedReader;
import java.io.File;
import java.io.StringReader;

/**
 * @version $Revision: 1039088 $
 */
public class CloseableTemplateTest extends TestCase {

    public void testCloseable() throws Exception {

        Boolean answer = new CloseableTemplate<BufferedReader, Boolean>() {
            @Override
            protected Boolean doUse(BufferedReader stream) throws Exception {
                return stream.readLine().contains("world");
            }
        }.use(new BufferedReader(new StringReader("hello world")));

        Assert.assertEquals("Should have found the world text!", Boolean.TRUE, answer);
    }

}