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在學(xué)習(xí)Java的過(guò)程中，想必大家都一定學(xué)習(xí)過(guò)異常這個(gè)篇章，異常的基本特性和使用這里就不再多講了。什么是異常？我不知道大家都是怎么去理解的，我的理解很簡(jiǎn)單，那就是不正常的情況，比如我現(xiàn)在是個(gè)男的，但是我卻有著女人所獨(dú)有的東西，在我看來(lái)這尼瑪肯定是種異常，簡(jiǎn)直不能忍。想必大家都能夠理解看懂，并正確使用。
但是，光學(xué)會(huì)基本異常處理和使用不夠的，在工作中出現(xiàn)異常并不可怕，有時(shí)候是需要使用異常來(lái)驅(qū)動(dòng)業(yè)務(wù)的處理，例如: 在使用唯一約束的數(shù)據(jù)庫(kù)的時(shí)候，如果插入一條重復(fù)的數(shù)據(jù)，那么可以通過(guò)捕獲唯一約束異常DuplicateKeyException來(lái)進(jìn)行處理，這個(gè)時(shí)候，在server層中就可以向調(diào)用層拋出對(duì)應(yīng)的狀態(tài)，上層根據(jù)對(duì)應(yīng)的狀態(tài)再進(jìn)行處理，所以有時(shí)候異常對(duì)業(yè)務(wù)來(lái)說(shuō)，是一個(gè)驅(qū)動(dòng)方式。
有的捕獲異常之后會(huì)將異常進(jìn)行輸出，不知道細(xì)心的同學(xué)有沒(méi)有注意到一點(diǎn)，輸出的異常是什么東西呢？
下面來(lái)看一個(gè)常見(jiàn)的異常：
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)
一個(gè)空指針異常:
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)
大家有沒(méi)有發(fā)現(xiàn)一個(gè)特點(diǎn)，就是異常的輸出是中能夠精確的輸出異常出現(xiàn)的地點(diǎn)，還有后面一大堆的執(zhí)行過(guò)程類調(diào)用，也都打印出來(lái)了，這些信息從哪兒來(lái)呢？ 這些信息是從棧中獲取的，在打印異常日志的時(shí)候，會(huì)從棧中去獲取這些調(diào)用信息。能夠精確的定位異常出現(xiàn)的異常當(dāng)然是好，但是我們有時(shí)候考慮到程序的性能，以及一些需求時(shí)，我們有時(shí)候并不需要完全的打印這些信息，并且去方法調(diào)用棧中獲取相應(yīng)的信息，是有性能消耗的，對(duì)于一些性能要求高的程序，我們完全可以在這一個(gè)方面為程序性能做一個(gè)提升。
所以如何避免輸出這些堆棧信息呢？ 那么自定義異常就可以解決這個(gè)問(wèn)題：
首先，自動(dòng)異常需要繼承RuntimeException, 然后，再通過(guò)是重寫fillInStackTrace, toString 方法， 例如，下面我定義一個(gè)AppException異常:
package com.green.monitor.common.exception;
import java.text.MessageFormat;
/**
* 自定義異常類
*/
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);
}
}那么為什么要重寫fillInStackTrace, 和 toString 方法呢？ 我們首先來(lái)看源碼是怎么一回事.
public class RuntimeException extends Exception {
static final long serialVersionUID = -7034897190745766939L;
/** Constructs a new runtime exception with null 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是繼承Exception,但是它里面去只是調(diào)用了父類的方法，本身是沒(méi)有做什么其余的操作。那么繼續(xù)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 null 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);
}
}
從源碼中可以看到, Exception里面也是直接調(diào)用了父類的方法，和RuntimeException一樣，自己其實(shí)并沒(méi)有做什么。 那么直接來(lái)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 this Throwable 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 *
從源碼中可以看到，到Throwable就幾乎到頭了， 在fillInStackTrace() 方法是一個(gè)native方法，這方法也就是會(huì)調(diào)用底層的C語(yǔ)言，返回一個(gè)Throwable對(duì)象, toString 方法，返回的是throwable的簡(jiǎn)短描述信息， 并且在getStackTrace 方法和 getOurStackTrace 中調(diào)用的都是native方法getStackTraceElement, 而這個(gè)方法是返回指定的棧元素信息，所以這個(gè)過(guò)程肯定是消耗性能的，那么我們自定義異常中的重寫toString方法和fillInStackTrace方法就可以不從棧中去獲取異常信息，直接輸出，這樣對(duì)系統(tǒng)和程序來(lái)說(shuō)，相對(duì)就沒(méi)有那么”重”, 是一個(gè)優(yōu)化性能的非常好的辦法。那么如果出現(xiàn)自定義異常那么是什么樣的呢？請(qǐng)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","空指針異常");
}
}那么在異常異常的時(shí)候，系統(tǒng)將會(huì)打印我們自定義的異常信息:
000001[空指針異常] Process finished with exit code -1
所以特別簡(jiǎn)潔，優(yōu)化了系統(tǒng)程序性能，讓程序不這么“重”, 所以對(duì)于性能要求特別要求的系統(tǒng)。趕緊自己的自定義異常吧！
總結(jié)
以上就是這篇文章的全部?jī)?nèi)容了，希望本文的內(nèi)容對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，如果有疑問(wèn)大家可以留言交流，謝謝大家對(duì)創(chuàng)新互聯(lián)的支持。
當(dāng)前名稱：Java如何自定義異常打印非堆棧信息詳解
標(biāo)題來(lái)源：http://fisionsoft.com.cn/article/jghogc.html
