Java Throwable源码解读
package java.lang; import java.io.*; /** * * Throwable是所有Error和Exceptiong的父类 * 注意它有四个构造函数: * Throwable() * Throwable(String message) * Throwable(Throwable cause) * Throwable(String message, Throwable cause) * */ public class Throwable implements Serializable { private static final long serialVersionUID = -3042686055658047285L; /** * Native code saves some indication of the stack backtrace in this slot. */ private transient Object backtrace; /** * 描述此异常的信息 */ private String detailMessage; /** * 表示当前异常由那个Throwable引起 * 如果为null表示此异常不是由其他Throwable引起的 * 如果此对象与自己相同,表明此异常的起因对象还没有被初始化 */ private Throwable cause = this; /** * 描述异常轨迹的数组 */ private StackTraceElement[] stackTrace; /** * 构造函数,起因对象没有被初始化可以在以后使用initCause进行初始化 * fillInStackTrace可以用来初始化它的异常轨迹的数组 */ public Throwable() { fillInStackTrace(); } /** * 构造函数 */ public Throwable(String message) { //填充异常轨迹数组 fillInStackTrace(); //初始化异常描述信息 detailMessage = message; } /** * 构造函数,cause表示起因对象 */ public Throwable(String message, Throwable cause) { fillInStackTrace(); detailMessage = message; this.cause = cause; } /** * 构造函数 */ public Throwable(Throwable cause) { fillInStackTrace(); detailMessage = (cause==null ? null : cause.toString()); this.cause = cause; } /** * 获取详细信息 */ public String getMessage() { return detailMessage; } /** * 获取详细信息 */ public String getLocalizedMessage() { return getMessage(); } /** * 获取起因对象 */ 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 */ public synchronized Throwable initCause(Throwable cause) { //如果不是未初始化状态则抛出异常 if (this.cause != this) throw new 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) throw new IllegalArgumentException("Self-causation not permitted"); //设置起因对象 this.cause = cause; //返回设置的起因的对象 return this; } /** * 字符串表示形式 */ public String toString() { String s = getClass().getName(); String message = getLocalizedMessage(); return (message != null) ? (s + ": " + message) : s; } /** * 打印出错误轨迹 */ public void printStackTrace() { printStackTrace(System.err); } /** * 打印出错误轨迹 */ public void printStackTrace(PrintStream s) { synchronized (s) { //调用当前对象的toString方法 s.println(this); //获取异常轨迹数组 StackTraceElement[] trace = getOurStackTrace(); //打印出每个元素的字符串表示 for (int i=0; i < trace.length; i++) s.println("\tat " + trace[i]); //获取起因对象 Throwable ourCause = getCause(); //递归的打印出起因对象的信息 if (ourCause != null) ourCause.printStackTraceAsCause(s, trace); } } /** * 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 */ private void printStackTraceAsCause(PrintStream s, StackTraceElement[] causedTrace) { //获得当前的异常轨迹 StackTraceElement[] trace = getOurStackTrace(); //m为当前异常轨迹数组的最后一个元素位置, //n为当前对象引起的异常的异常轨迹数组的最后一个元素 int m = trace.length-1, n = causedTrace.length-1; //分别从两个数组的后面做循环,如果相等则一直循环,直到不等或数组到头 while (m >= 0 && n >=0 && trace[m].equals(causedTrace[n])) { m--; n--; } //相同的个数 int framesInCommon = trace.length - 1 - m; //打印出不同的错误轨迹 s.println("Caused by: " + this); for (int i=0; i <= m; i++) s.println("\tat " + trace[i]); //如果有相同的则打印出相同的个数 if (framesInCommon != 0) s.println("\t... " + framesInCommon + " more"); //获得此对象的起因对象,并递归打印出信息 Throwable ourCause = getCause(); if (ourCause != null) ourCause.printStackTraceAsCause(s, trace); } /** * 打印出错误轨迹 */ public void 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); } } /** * 打印起因对象的信息 */ private void printStackTraceAsCause(PrintWriter s, StackTraceElement[] causedTrace) { // assert Thread.holdsLock(s); // Compute number of frames in common between this and caused StackTraceElement[] trace = getOurStackTrace(); int m = trace.length-1, n = causedTrace.length-1; while (m >= 0 && n >=0 && trace[m].equals(causedTrace[n])) { 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"); // Recurse if we have a cause Throwable ourCause = getCause(); if (ourCause != null) ourCause.printStackTraceAsCause(s, trace); } /** * 填充异常轨迹 */ public synchronized native Throwable fillInStackTrace(); /** * 返回当前的异常轨迹的拷贝 */ public StackTraceElement[] getStackTrace() { return (StackTraceElement[]) getOurStackTrace().clone(); } /** * 获取当前的异常轨迹 */ private synchronized StackTraceElement[] getOurStackTrace() { //如果第一次调用此方法则初始化异常轨迹数组 if (stackTrace == null) { //获得异常轨迹深度 int depth = getStackTraceDepth(); //创建新的异常轨迹数组,并填充它 stackTrace = new StackTraceElement[depth]; for (int i=0; i < depth; i++) stackTrace[i] = getStackTraceElement(i);//获取指定位标的异常轨迹 } return stackTrace; } /** * 设置异常轨迹 */ public void setStackTrace(StackTraceElement[] stackTrace) { //拷贝设置参数 StackTraceElement[] defensiveCopy = (StackTraceElement[]) stackTrace.clone(); //如果设置参数有空元素则抛出异常 for (int i = 0; i < defensiveCopy.length; i++) if (defensiveCopy[i] == null) throw new NullPointerException("stackTrace[" + i + "]"); //设置当前对象的异常轨迹 this.stackTrace = defensiveCopy; } /** * 异常轨迹的深度,0表示无法获得 */ private native int getStackTraceDepth(); /** * 获取指定位标的异常轨迹 */ private native StackTraceElement getStackTraceElement(int index); private synchronized void writeObject(java.io.ObjectOutputStream s) throws IOException { getOurStackTrace(); s.defaultWriteObject(); } }
转载至：http://blog.csdn.net/ramprog/article/details/47689963
