nestedcheckedexception.java

一个关于Spring框架的示例应用程序,简单使用,可以参考.

/*
 * Copyright 2002-2004 the original author or authors.
 * 
 * Licensed 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.springframework.core;

import java.io.PrintStream;
import java.io.PrintWriter;

/**
 * Handy class for wrapping checked Exceptions with a root cause.
 *
 * <p>This time-honoured technique is no longer necessary in Java 1.4, which
 * finally provides built-in support for exception nesting. Thus exceptions in
 * applications written to use Java 1.4 need not extend this class. To ease
 * migration, this class mirrors Java 1.4's nested exceptions as closely as possible.
 *
 * <p>Abstract to force the programmer to extend the class. getMessage will include
 * nested exception information; printStackTrace etc will delegate to the wrapped
 * exception, if any.
 *
 * <p>The similarity between this class and the NestedCheckedException class is
 * unavoidable, as Java forces these two classes to have different superclasses
 * (ah, the inflexibility of concrete inheritance!).
 *
 * <p>As discussed in
 * <a href="http://www.amazon.com/exec/obidos/tg/detail/-/0764543857/">Expert One-On-One J2EE Design and Development</a>,
 * runtime exceptions are often a better alternative to checked exceptions.
 * However, all exceptions should preserve their stack trace, if caused by a
 * lower-level exception.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see #getMessage
 * @see #printStackTrace
 */
public abstract class NestedCheckedException extends Exception {

	/** Root cause of this nested exception */
	private Throwable cause;

	/**
	 * Construct a <code>NestedCheckedException</code> with the specified detail message.
	 * @param msg the detail message
	 */
	public NestedCheckedException(String msg) {
		super(msg);
	}

	/**
	 * Construct a <code>NestedCheckedException</code> with the specified detail message
	 * and nested exception.
	 * @param msg the detail message
	 * @param ex the nested exception
	 */
	public NestedCheckedException(String msg, Throwable ex) {
		super(msg);
		this.cause = ex;
	}

	/**
	 * Return the nested cause, or null if none.
	 */
	public Throwable getCause() {
		return (this.cause == this ? null : this.cause);
	}

	/**
	 * Return the detail message, including the message from the nested exception
	 * if there is one.
	 */
	public String getMessage() {
		// Even if you cannot set the cause of this exception other than through
		// the constructor, we check for the cause being "this" here, as the cause
		// could still be set to "this" via reflection: for example, by a remoting
		// deserializer like Hessian's.
		if (this.cause == null || this.cause == this) {
			return super.getMessage();
		}
		else {
			return super.getMessage() + "; nested exception is " + this.cause.getClass().getName() +
					": " + this.cause.getMessage();
		}
	}

	/**
	 * Print the composite message and the embedded stack trace to the specified stream.
	 * @param ps the print stream
	 */
	public void printStackTrace(PrintStream ps) {
		if (this.cause == null || this.cause == this) {
			super.printStackTrace(ps);
		}
		else {
			ps.println(this);
			this.cause.printStackTrace(ps);
		}
	}

	/**
	 * Print the composite message and the embedded stack trace to the specified print writer.
	 * @param pw the print writer
	 */
	public void printStackTrace(PrintWriter pw) {
		if (this.cause == null || this.cause == this) {
			super.printStackTrace(pw);
		}
		else {
			pw.println(this);
			this.cause.printStackTrace(pw);
		}
	}

	/**
	 * Check whether this exception contains an exception of the given class:
	 * either it is of the given class itself or it contains a nested cause
	 * of the given class.
	 * <p>Currently just traverses NestedCheckedException causes. Will use
	 * the JDK 1.4 exception cause mechanism once Spring requires JDK 1.4.
	 * @param exClass the exception class to look for
	 */
	public boolean contains(Class exClass) {
		if (exClass == null) {
			return false;
		}
		Throwable ex = this;
		while (ex != null) {
			if (exClass.isInstance(ex)) {
				return true;
			}
			if (ex instanceof NestedCheckedException) {
				// Cast is necessary on JDK 1.3, where Throwable does not
				// provide a "getCause" method itself.
				ex = ((NestedCheckedException) ex).getCause();
			}
			else {
				ex = null;
			}
		}
		return false;
	}

}