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，谢谢大家对武林网的支持。