Java中Throwable源码阅读

Throwable 源码阅读笔记

读的不是很懂，但是大致明白自定义异常中的那几个常用的参数的发源地了，这是项目中自定义异常经常使用的几个参数和方法，在Throwable中都可以查到影子：

protected StringpositionName;

protected String labelName;

protected String message="";

public String getMessage() {

return message;

}

Throwable 源码

package com.cloud.exe; import java.io.*; /** * Throwable * 异常，可抛出的异常类 */ publicclass Throwableimplements Serializable { /** * Java的序列化机制是通过在运行时判断类的serialVersionUID来验证版本一致性的。在进行反序列化时， * JVM会把传来的字节流中的serialVersionUID与本地相应实体（类）的serialVersionUID进行比较 * 如果相同就认为是一致的，可以进行反序列化，否则就会出现序列化版本不一致的异常。(InvalidCastException) */ privatestaticfinallongserialVersionUID = -3042686055658047285L; /** * 关于异常的细节：比如文件找不到的异常，这个detailMessage可以记录为什么文件找不到 */ private StringdetailMessage; /** * 异常的实力：初始化的时候默认是本身 */ private Throwablecause =this; /** * 异常轨迹最后的元素 */ private StackTraceElement[]stackTrace; /** * 四个构造方法 */ public Throwable() { fillInStackTrace(); } public Throwable(String message) { fillInStackTrace(); detailMessage = message; } public Throwable(String message, Throwable cause) { fillInStackTrace(); detailMessage = message; this.cause = cause; } public Throwable(Throwable cause) { fillInStackTrace(); detailMessage = (cause==null ?null : cause.toString()); this.cause = cause; } /** * 自定义异常的时候，一般重写该方法，满足业务需要 * @return */ public String getMessage() { returndetailMessage; } /** * 一般不适用，多处理资源国际化问题 * @return */ public String getLocalizedMessage() { return getMessage(); } /** * 如果cause=null,就扔回一个null * @return */ public Throwable getCause() { return (cause==this ?null : cause); } /** * 初始化起因对象,这个方法只能在未被初始化的情况下调用一次 */ publicsynchronized Throwable initCause(Throwable cause) { //如果不是未初始化状态则抛出异常 if (this.cause !=this) thrownew IllegalStateException("Can't overwrite cause"); //要设置的起因对象与自身相等则抛出异常 if (cause ==this) thrownew IllegalArgumentException("Self-causation not permitted"); //设置起因 this.cause = cause; returnthis; } /** * 把异常信息转成字符串信息 */ public String toString() { String s = getClass().getName(); String message = getLocalizedMessage(); return (message !=null) ? (s +": " + message) : s; } /** * 打印异常轨迹 */ publicvoid printStackTrace() { printStackTrace(System.err); } /** * 打印异常轨迹 * @param s */ publicvoid printStackTrace(PrintStream s) { synchronized (s) { s.println(this); StackTraceElement[] trace = getOurStackTrace(); for (int i=0; i < trace.length; i++) s.println("\tat " + trace[i]); Throwable ourCause = getCause(); //递归打印出起因信息 if (ourCause !=null) ourCause.printStackTraceAsCause(s, trace); } } /** * P打印起因对象的信息 * @param s打印的流 * @param causedTrace有此对象引起的异常的异常轨迹 */ privatevoid printStackTraceAsCause(PrintStream s, StackTraceElement[] causedTrace) { //获取当前的异常信息 StackTraceElement[] trace = getOurStackTrace(); int m = trace.length-1, n = causedTrace.length-1; while (m >= 0 && n >=0 && trace[m].equals(causedTrace )) { m--; n--; } int framesInCommon = trace.length - 1 - m; s.println("Caused by: " +this); for (int i=0; i <= m; i++) s.println("\tat " + trace[i]); if (framesInCommon != 0) s.println("\t... " + framesInCommon +" more"); Throwable ourCause = getCause(); if (ourCause !=null) ourCause.printStackTraceAsCause(s, trace); } /** * 打印错误信息 */ publicvoid printStackTrace(PrintWriter s) { synchronized (s) { s.println(this); StackTraceElement[] trace = getOurStackTrace(); for (int i=0; i < trace.length; i++) s.println("\tat " + trace[i]); Throwable ourCause = getCause(); if (ourCause !=null) ourCause.printStackTraceAsCause(s, trace); } } /** * 打印异常起因对象信息 */ privatevoid printStackTraceAsCause(PrintWriter s, StackTraceElement[] causedTrace) { StackTraceElement[] trace = getOurStackTrace(); int m = trace.length-1, n = causedTrace.length-1; while (m >= 0 && n >=0 && trace[m].equals(causedTrace )) { m--; n--; } int framesInCommon = trace.length - 1 - m; s.println("Caused by: " +this); for (int i=0; i <= m; i++) s.println("\tat " + trace[i]); if (framesInCommon != 0) s.println("\t... " + framesInCommon +" more"); Throwable ourCause = getCause(); if (ourCause !=null) ourCause.printStackTraceAsCause(s, trace); } /** * 异常轨迹填充 */ publicsynchronizednative Throwable fillInStackTrace(); /** * 返回异常信息的拷贝信息 */ public StackTraceElement[] getStackTrace() { return (StackTraceElement[]) getOurStackTrace().clone(); } /** * 获取当前异常的轨迹 * @return */ privatesynchronized StackTraceElement[] getOurStackTrace() { if (stackTrace ==null) { int depth = getStackTraceDepth(); stackTrace = new StackTraceElement[depth]; for (int i=0; i < depth; i++) stackTrace[i] = getStackTraceElement(i); } returnstackTrace; } /** * 设置异常轨迹 */ publicvoid setStackTrace(StackTraceElement[] stackTrace) { StackTraceElement[] defensiveCopy = (StackTraceElement[]) stackTrace.clone(); for (int i = 0; i < defensiveCopy.length; i++) if (defensiveCopy[i] ==null) thrownew NullPointerException("stackTrace[" + i +"]"); this.stackTrace = defensiveCopy; } /** * 异常轨迹的深度 */ nativeint getStackTraceDepth(); /** * 获取指定位标的异常轨迹 */ native StackTraceElement getStackTraceElement(int index); privatesynchronizedvoid writeObject(java.io.ObjectOutputStream s) throws IOException { getOurStackTrace(); s.defaultWriteObject(); } }