exceptionutil.java

Light in the box 抓取程序。 使用HttpClient

/*
 * $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//httpclient/src/java/org/apache/commons/httpclient/util/ExceptionUtil.java,v 1.5 2004/10/19 18:09:46 olegk Exp $
 * $Revision: 480424 $
 * $Date: 2006-11-29 06:56:49 +0100 (Wed, 29 Nov 2006) $
 *
 * ====================================================================
 *
 *  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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package org.apache.commons.httpclient.util;

import java.io.InterruptedIOException;
import java.lang.reflect.Method;

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

/**
 * The home for utility methods that handle various exception-related tasks.
 * 
 * @author <a href="mailto:[e-mail]">Oleg Kalnichevski</a>
 * @author <a href="mailto:[e-mail]">Laura Werner</a>
 * 
 * @since 3.0
 */
public class ExceptionUtil {

    /** Log object for this class. */
    private static final Log LOG = LogFactory.getLog(ExceptionUtil.class);

    /** A reference to Throwable's initCause method, or null if it's not there in this JVM */
    static private final Method INIT_CAUSE_METHOD = getInitCauseMethod();

    /** A reference to SocketTimeoutExceptionClass class, or null if it's not there in this JVM */
    static private final Class SOCKET_TIMEOUT_CLASS = SocketTimeoutExceptionClass();
    
    /**
     * Returns a <code>Method<code> allowing access to
     * {@link Throwable.initCause(Throwable) initCause} method of {@link Throwable},
     * or <code>null</code> if the method
     * does not exist.
     * 
     * @return A <code>Method<code> for <code>Throwable.initCause</code>, or
     * <code>null</code> if unavailable.
     */ 
    static private Method getInitCauseMethod() {
        try {
            Class[] paramsClasses = new Class[] { Throwable.class };
            return Throwable.class.getMethod("initCause", paramsClasses);
        } catch (NoSuchMethodException e) {
            return null;
        }
    }
    
    /**
     * Returns <code>SocketTimeoutExceptionClass<code> or <code>null</code> if the class
     * does not exist.
     * 
     * @return <code>SocketTimeoutExceptionClass<code>, or <code>null</code> if unavailable.
     */ 
    static private Class SocketTimeoutExceptionClass() {
        try {
            return Class.forName("java.net.SocketTimeoutException");
        } catch (ClassNotFoundException e) {
            return null;
        }
    }
    
    /** 
     * If we're running on JDK 1.4 or later, initialize the cause for the given throwable.
     * 
     * @param  throwable The throwable.
     * @param  cause     The cause of the throwable.
     */
    public static void initCause(Throwable throwable, Throwable cause) {
        if (INIT_CAUSE_METHOD != null) {
            try {
                INIT_CAUSE_METHOD.invoke(throwable, new Object[] { cause });
            } catch (Exception e) {
                LOG.warn("Exception invoking Throwable.initCause", e);
            }
        }
    }

    /** 
     * If SocketTimeoutExceptionClass is defined, returns <tt>true</tt> only if the 
     * exception is an instance of SocketTimeoutExceptionClass. If 
     * SocketTimeoutExceptionClass is undefined, always returns <tt>true</tt>. 
     * 
     * @param  e an instance of InterruptedIOException class.
     * 
     * @return <tt>true</tt> if the exception signals socket timeout, <tt>false</tt>
     *  otherwise.   
     */
    public static boolean isSocketTimeoutException(final InterruptedIOException e) {
        if (SOCKET_TIMEOUT_CLASS != null) {
            return SOCKET_TIMEOUT_CLASS.isInstance(e);
        } else {
            return true;
        }
    }
}