Java如何自定义异常打印非堆栈信息详解
前言
专注于为中小企业提供成都网站建设、网站设计服务,电脑端+手机端+微信端的三站合一,更高效的管理,为中小企业江南免费做网站提供优质的服务。我们立足成都,凝聚了一批互联网行业人才,有力地推动了成百上千企业的稳健成长,帮助中小企业通过网站建设实现规模扩充和转变。
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 withnull
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.Note that the detail message associated with *
cause
is not 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 null 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 (cause==null ? null : cause.toString()) * (which typically contains the class and detail message of * cause). 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 null 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 withnull
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.Note that the detail message associated with *
cause
is not 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 null 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 (cause==null ? null : cause.toString()) (which * typically contains the class and detail message of cause). * 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 null 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 *Throwable
object information about the current state of * the stack frames for the current thread. * * @return a reference to thisThrowable
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. * *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 * printStackTrace. * * @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 index < 0 || * index >= getStackTraceDepth() */ native StackTraceElement getStackTraceElement(int index); /** * Returns a short description of this throwable. * The result is the concatenation of: *
-
*
- the {@linkplain Class#getName() name} of the class of this object *
- ": " (a colon and a space) *
- the result of invoking this object's {@link #getLocalizedMessage} * method *
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,谢谢大家对创新互联的支持。
网页标题:Java如何自定义异常打印非堆栈信息详解
文章链接:http://scyanting.com/article/jghogc.html