Java如何自定义异常打印非堆栈信息详解

前言

在学习Java的过程中，想必大家都一定学习过异常这个篇章，异常的基本特性和使用这里就不再多讲了。什么是异常？我不知道大家都是怎么去理解的，我的理解很简单，那就是不正常的情况，比如我现在是个男的，但是我却有着女人所独有的东西，在我看来这尼玛肯定是种异常，简直不能忍。想必大家都能够理解看懂，并正确使用。

但是，光学会基本异常处理和使用不够的，在工作中出现异常并不可怕，有时候是需要使用异常来驱动业务的处理，例如: 在使用唯一约束的数据库的时候，如果插入一条重复的数据，那么可以通过捕获唯一约束异常DuplicateKeyException来进行处理，这个时候，在server层中就可以向调用层抛出对应的状态，上层根据对应的状态再进行处理，所以有时候异常对业务来说，是一个驱动方式。

有的捕获异常之后会将异常进行输出，不知道细心的同学有没有注意到一点，输出的异常是什么东西呢？

下面来看一个常见的异常：

java.lang.ArithmeticException: / by zero
 at greenhouse.ExceptionTest.testException(ExceptionTest.java:16)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
 at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
 at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
 at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
 at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76)
 at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
 at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
 at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
 at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
 at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
 at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
 at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
 at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
 at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
 at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
 at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
 at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

一个空指针异常:

java.lang.NullPointerException
 at greenhouse.ExceptionTest.testException(ExceptionTest.java:16)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
 at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
 at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
 at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
 at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76)
 at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
 at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
 at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
 at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
 at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
 at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
 at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
 at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
 at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
 at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
 at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
 at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

大家有没有发现一个特点，就是异常的输出是中能够精确的输出异常出现的地点，还有后面一大堆的执行过程类调用，也都打印出来了，这些信息从哪儿来呢？ 这些信息是从栈中获取的，在打印异常日志的时候，会从栈中去获取这些调用信息。能够精确的定位异常出现的异常当然是好，但是我们有时候考虑到程序的性能，以及一些需求时，我们有时候并不需要完全的打印这些信息，并且去方法调用栈中获取相应的信息，是有性能消耗的，对于一些性能要求高的程序，我们完全可以在这一个方面为程序性能做一个提升。

所以如何避免输出这些堆栈信息呢？ 那么自定义异常就可以解决这个问题：

首先，自动异常需要继承RuntimeException, 然后，再通过是重写fillInStackTrace, toString 方法， 例如，下面我定义一个AppException异常:

package com.green.monitor.common.exception;
import java.text.MessageFormat;
/**
 * 自定义异常类
 */
public class AppException extends RuntimeException {
 private boolean isSuccess = false;
 private String key;
 private String info;
 public AppException(String key) {
 super(key);
 this.key = key;
 this.info = key;
 }
 public AppException(String key, String message) {
 super(MessageFormat.format("{0}[{1}]", key, message));
 this.key = key;
 this.info = message;
 }
 public AppException(String message, String key, String info) {
 super(message);
 this.key = key;
 this.info = info;
 }
 public boolean isSuccess() {
 return isSuccess;
 }
 public String getKey() {
 return key;
 }
 public void setKey(String key) {
 this.key = key;
 }
 public String getInfo() {
 return info;
 }
 public void setInfo(String info) {
 this.info = info;
 }
 @Override
 public Throwable fillInStackTrace() {
 return this;
 }
 @Override
 public String toString() {
 return MessageFormat.format("{0}[{1}]",this.key,this.info);
 }
}

那么为什么要重写fillInStackTrace, 和 toString 方法呢？ 我们首先来看源码是怎么一回事.

public class RuntimeException extends Exception {
 static final long serialVersionUID = -7034897190745766939L;
 /** Constructs a new runtime exception with <code>null</code> as its
 * detail message. The cause is not initialized, and may subsequently be
 * initialized by a call to {@link #initCause}.
 */
 public RuntimeException() {
 super();
 }
 /** Constructs a new runtime exception with the specified detail message.
 * The cause is not initialized, and may subsequently be initialized by a
 * call to {@link #initCause}.
 *
 * @param message the detail message. The detail message is saved for
 *  later retrieval by the {@link #getMessage()} method.
 */
 public RuntimeException(String message) {
 super(message);
 }
 /**
 * Constructs a new runtime exception with the specified detail message and
 * cause. <p>Note that the detail message associated with
 * <code>cause</code> is <i>not</i> automatically incorporated in
 * this runtime exception's detail message.
 *
 * @param message the detail message (which is saved for later retrieval
 *  by the {@link #getMessage()} method).
 * @param cause the cause (which is saved for later retrieval by the
 *  {@link #getCause()} method). (A <tt>null</tt> value is
 *  permitted, and indicates that the cause is nonexistent or
 *  unknown.)
 * @since 1.4
 */
 public RuntimeException(String message, Throwable cause) {
 super(message, cause);
 }
 /** Constructs a new runtime exception with the specified cause and a
 * detail message of <tt>(cause==null ? null : cause.toString())</tt>
 * (which typically contains the class and detail message of
 * <tt>cause</tt>). This constructor is useful for runtime exceptions
 * that are little more than wrappers for other throwables.
 *
 * @param cause the cause (which is saved for later retrieval by the
 *  {@link #getCause()} method). (A <tt>null</tt> value is
 *  permitted, and indicates that the cause is nonexistent or
 *  unknown.)
 * @since 1.4
 */
 public RuntimeException(Throwable cause) {
 super(cause);
 }
}

RuntimeException是继承Exception,但是它里面去只是调用了父类的方法，本身是没有做什么其余的操作。那么继续看Exception里面是怎么回事呢？

public class Exception extends Throwable {
 static final long serialVersionUID = -3387516993124229948L;
 /**
 * Constructs a new exception with <code>null</code> as its detail message.
 * The cause is not initialized, and may subsequently be initialized by a
 * call to {@link #initCause}.
 */
 public Exception() {
 super();
 }
 /**
 * Constructs a new exception with the specified detail message. The
 * cause is not initialized, and may subsequently be initialized by
 * a call to {@link #initCause}.
 *
 * @param message the detail message. The detail message is saved for
 *  later retrieval by the {@link #getMessage()} method.
 */
 public Exception(String message) {
 super(message);
 }
 /**
 * Constructs a new exception with the specified detail message and
 * cause. <p>Note that the detail message associated with
 * <code>cause</code> is <i>not</i> automatically incorporated in
 * this exception's detail message.
 *
 * @param message the detail message (which is saved for later retrieval
 *  by the {@link #getMessage()} method).
 * @param cause the cause (which is saved for later retrieval by the
 *  {@link #getCause()} method). (A <tt>null</tt> value is
 *  permitted, and indicates that the cause is nonexistent or
 *  unknown.)
 * @since 1.4
 */
 public Exception(String message, Throwable cause) {
 super(message, cause);
 }
 /**
 * Constructs a new exception with the specified cause and a detail
 * message of <tt>(cause==null ? null : cause.toString())</tt> (which
 * typically contains the class and detail message of <tt>cause</tt>).
 * This constructor is useful for exceptions that are little more than
 * wrappers for other throwables (for example, {@link
 * java.security.PrivilegedActionException}).
 *
 * @param cause the cause (which is saved for later retrieval by the
 *  {@link #getCause()} method). (A <tt>null</tt> value is
 *  permitted, and indicates that the cause is nonexistent or
 *  unknown.)
 * @since 1.4
 */
 public Exception(Throwable cause) {
 super(cause);
 }
}

从源码中可以看到, Exception里面也是直接调用了父类的方法，和RuntimeException一样，自己其实并没有做什么。 那么直接来看Throwable里面是怎么一回事:

public class Throwable implements Serializable {
 public Throwable(String message) {
 fillInStackTrace();
 detailMessage = message;
 }

 /**
 * Fills in the execution stack trace. This method records within this
 * <code>Throwable</code> object information about the current state of
 * the stack frames for the current thread.
 *
 * @return a reference to this <code>Throwable</code> instance.
 * @see java.lang.Throwable#printStackTrace()
 */
 public synchronized native Throwable fillInStackTrace();

 /**
 * Provides programmatic access to the stack trace information printed by
 * {@link #printStackTrace()}. Returns an array of stack trace elements,
 * each representing one stack frame. The zeroth element of the array
 * (assuming the array's length is non-zero) represents the top of the
 * stack, which is the last method invocation in the sequence. Typically,
 * this is the point at which this throwable was created and thrown.
 * The last element of the array (assuming the array's length is non-zero)
 * represents the bottom of the stack, which is the first method invocation
 * in the sequence.
 *
 * <p>Some virtual machines may, under some circumstances, omit one
 * or more stack frames from the stack trace. In the extreme case,
 * a virtual machine that has no stack trace information concerning
 * this throwable is permitted to return a zero-length array from this
 * method. Generally speaking, the array returned by this method will
 * contain one element for every frame that would be printed by
 * <tt>printStackTrace</tt>.
 *
 * @return an array of stack trace elements representing the stack trace
 *  pertaining to this throwable.
 * @since 1.4
 */
 public StackTraceElement[] getStackTrace() {
 return (StackTraceElement[]) getOurStackTrace().clone();
 }
 private synchronized StackTraceElement[] getOurStackTrace() {
 // Initialize stack trace if this is the first call to this method
 if (stackTrace == null) {
  int depth = getStackTraceDepth();
  stackTrace = new StackTraceElement[depth];
  for (int i=0; i < depth; i++)
  stackTrace[i] = getStackTraceElement(i);
 }
 return stackTrace;
 }

 /**
 * Returns the number of elements in the stack trace (or 0 if the stack
 * trace is unavailable).
 *
 * package-protection for use by SharedSecrets.
 */
 native int getStackTraceDepth();
 /**
 * Returns the specified element of the stack trace.
 *
 * package-protection for use by SharedSecrets.
 *
 * @param index index of the element to return.
 * @throws IndexOutOfBoundsException if <tt>index < 0 ||
 *  index >= getStackTraceDepth() </tt>
 */
 native StackTraceElement getStackTraceElement(int index);

 /**
 * Returns a short description of this throwable.
 * The result is the concatenation of:
 * <ul>
 * <li> the {@linkplain Class#getName() name} of the class of this object
 * <li> ": " (a colon and a space)
 * <li> the result of invoking this object's {@link #getLocalizedMessage}
 * method
 * </ul>
 * If <tt>getLocalizedMessage</tt> returns <tt>null</tt>, then just
 * the class name is returned.
 *
 * @return a string representation of this throwable.
 */
 public String toString() {
 String s = getClass().getName();
 String message = getLocalizedMessage();
 return (message != null) ? (s + ": " + message) : s;
 }

从源码中可以看到，到Throwable就几乎到头了， 在fillInStackTrace() 方法是一个native方法，这方法也就是会调用底层的C语言，返回一个Throwable对象, toString 方法，返回的是throwable的简短描述信息， 并且在getStackTrace 方法和 getOurStackTrace 中调用的都是native方法getStackTraceElement, 而这个方法是返回指定的栈元素信息，所以这个过程肯定是消耗性能的，那么我们自定义异常中的重写toString方法和fillInStackTrace方法就可以不从栈中去获取异常信息，直接输出，这样对系统和程序来说，相对就没有那么”重”, 是一个优化性能的非常好的办法。那么如果出现自定义异常那么是什么样的呢？请看下面吧:

@Test
 public void testException(){
 try {
 String str =null;
 System.out.println(str.charAt(0));
 }catch (Exception e){
 throw new AppException("000001","空指针异常");
 }
 }

那么在异常异常的时候，系统将会打印我们自定义的异常信息:

000001[空指针异常]
Process finished with exit code -1

所以特别简洁，优化了系统程序性能，让程序不这么“重”, 所以对于性能要求特别要求的系统。赶紧自己的自定义异常吧！

总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对我们的支持。

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