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();
}
}
