重新抛出异常——fillInStackTrace()

如果只是把当前的异常对象重新抛出，那么printStackTrace()方法显示的将是原来异常抛出点的调用栈信息，而并非重新抛出点的信息。要想更新这个信息，可以使用fillInStackTrace()方法，这将返回一个Throwable对象，他是通过把当前调用栈信息填入原来的那个异常对象而建立的。如下代码所示：

public class Rethowing {
	public static void f() throws Exception {
		System.out.println("originating the exception in f()");
		throw new Exception("throw from f()");
	}

	public static void g() throws Exception {
		try {
			f();
		} catch (Exception e) {
			System.out.println("Inside g(),e.printStackTrace()");
			e.printStackTrace(System.out);
			throw e;
		}
	}
	
	public static void h() throws Exception {
		try {
			f();
		} catch (Exception e) {
			System.out.println("Inside h(),e.printStackTrace()");
			e.printStackTrace(System.out);
			throw (Exception) e.fillInStackTrace();
		}
	}
	
	public static void main(String[] args) {
		try {
			g();
		} catch (Exception e) {
			System.out.println("main: printStackTrace()");
			e.printStackTrace(System.out);
		}
		System.out.println("--------");
		try {
			h();
		} catch (Exception e) {
			System.out.println("main: printStackTrace()");
			e.printStackTrace(System.out);
		}
	}
}

输入如下：

originating the exception in f()
Inside g(),e.printStackTrace()
java.lang.Exception: throw from f()
	at chapter12.t1.Rethowing.f(Rethowing.java:6)
	at chapter12.t1.Rethowing.g(Rethowing.java:11)
	at chapter12.t1.Rethowing.main(Rethowing.java:31)
main: printStackTrace()
java.lang.Exception: throw from f()
	at chapter12.t1.Rethowing.f(Rethowing.java:6)
	at chapter12.t1.Rethowing.g(Rethowing.java:11)
	at chapter12.t1.Rethowing.main(Rethowing.java:31)
--------
originating the exception in f()
Inside h(),e.printStackTrace()
java.lang.Exception: throw from f()
	at chapter12.t1.Rethowing.f(Rethowing.java:6)
	at chapter12.t1.Rethowing.h(Rethowing.java:21)
	at chapter12.t1.Rethowing.main(Rethowing.java:38)
main: printStackTrace()
java.lang.Exception: throw from f()
	at chapter12.t1.Rethowing.h(Rethowing.java:25)
	at chapter12.t1.Rethowing.main(Rethowing.java:38)

对比main方法中两次方法调用，可以发现调用fillInStackTrace()的那一行成了异常发生的。