java.lang.reflect.Proxy:巨大的异常堆栈跟踪
java.lang.reflect.Proxy: Huge exception stack trace
这是一个简单的 Java 应用程序:
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class Main {
interface MyInterface {
void myMethod();
}
public static void main(String[] args) {
MyInterface myInterface = (MyInterface) Proxy.newProxyInstance(Main.class.getClassLoader(), new Class[] {MyInterface.class},
new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
return method.invoke(proxy, args);
}
});
myInterface.myMethod();
}
}
我希望在这里得到一个简单的 WhosebugError
,因为我在代理实例上递归调用相同的方法。
但是,异常产生的堆栈跟踪包含数百万行和数百 MB 的大小。
堆栈跟踪的第一部分是这样开始的:
java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
at Main.main(Main.java:22)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
... 2 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
... 7 more
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
... 8 more
并扩展到:
Caused by: java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
... 1022 more
然后跟随数百万行,例如:
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
at $Proxy0.myMethod(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
.......
和:
Caused by: java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
at $Proxy0.myMethod(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
.......
最后打印的行是(在上面的重复序列之后):
Exception: java.lang.WhosebugError thrown from the UncaughtExceptionHandler in thread "main"
我怀疑堆栈跟踪生成机制正在调用代理实例上的一些方法(可能 toString
打印它,或者其他什么),从而一遍又一遍地重复递归(因为每个方法调用代理导致无限递归),但代理方法执行的总计数为 1919(通过在 InvocationHandler.invoke
方法中递增计数器来测量)。
在我的实际用例中,我当然解决了无限递归问题;我很好奇是否有人知道这是错误还是有合理的解释?
Java版本:
java version "1.8.0_65"
Java(TM) SE Runtime Environment (build 1.8.0_65-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.65-b01, mixed mode)
编辑
@JiriTousek 和@AndrewWilliamson 友善地分析了这可能是什么原因。我根据他们的输入实现了模拟:
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.UndeclaredThrowableException;
public class Test {
private static int counter = 0;
public static void main(String[] args) {
proxy();
}
private static void proxy() {
try {
methodInvoke();
} catch (Throwable e) {
throw new UndeclaredThrowableException(e);
}
}
private static void methodInvoke() throws InvocationTargetException {
try {
myMethod();
} catch (Throwable e) {
throw new InvocationTargetException(e);
}
}
private static void myMethod() {
if (counter++ == 5) {
throw new WhosebugError();
}
proxy();
}
}
这导致以下堆栈跟踪:
Exception in thread "main" java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.main(Test.java:9)
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 1 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 2 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 4 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 5 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 7 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 8 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 10 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 11 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 13 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 14 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 16 more
Caused by: java.lang.WhosebugError
at Test.myMethod(Test.java:30)
at Test.methodInvoke(Test.java:22)
... 17 more
因此,每个堆栈帧的行号没有增长。
我对此堆栈跟踪的解释是:
- 当最后发生堆栈溢出时,抛出一个
WhosebugError
- 此错误已被
method.invoke()
捕获并转换为 InvocationTargetException
(根据 it's javadoc),原因是原始异常
- 由于这个异常是一个已检查的异常,Proxy 不能让它自己掉下来,所以它捕获了它并将它翻译成一个
UndeclaredThrowableException
,再次将前一个作为原因
这样,对于堆栈溢出之前的每个递归级别,您都会得到另外两个 "caused by" 异常及其堆栈跟踪 - 大量输出。至于产量多少,大家猜一猜:
- 根据您的 post
,大约 2000 次调用
- 在每次调用中,堆栈跟踪似乎增长了 5 行
- 为每次调用打印 2 个错误和堆栈跟踪
所以最大的堆栈跟踪将有大约 10000 行,平均堆栈跟踪将有大约 5000 行,所有内容都打印两次(每种异常类型一次),总计约为 2000 * 5000 * 2
= 2000万行.
当相同跟踪的深度超过 1024(默认值)时,打印的堆栈跟踪不是 truncated。这就是为什么最后一个截断的跟踪以 ... 1022 more
结尾,而所有后续跟踪都被完整打印的原因。
可以通过将 MaxJavaStackTraceDepth
JVM 参数设置为所需的值来更改默认值。当我将 Proxy
的原始示例增加到 运行 它与 -XX:MaxJavaStackTraceDepth=8192
时,整个打印的堆栈跟踪下降到大约 12500 行,以:
结尾
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at Main1.invoke(Main1.java:16)
... 7003 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
... 7007 more
Exception: java.lang.WhosebugError thrown from the UncaughtExceptionHandler in thread "main"
这是一个简单的 Java 应用程序:
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class Main {
interface MyInterface {
void myMethod();
}
public static void main(String[] args) {
MyInterface myInterface = (MyInterface) Proxy.newProxyInstance(Main.class.getClassLoader(), new Class[] {MyInterface.class},
new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
return method.invoke(proxy, args);
}
});
myInterface.myMethod();
}
}
我希望在这里得到一个简单的 WhosebugError
,因为我在代理实例上递归调用相同的方法。
但是,异常产生的堆栈跟踪包含数百万行和数百 MB 的大小。
堆栈跟踪的第一部分是这样开始的:
java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
at Main.main(Main.java:22)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
... 2 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
... 7 more
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
... 8 more
并扩展到:
Caused by: java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
... 1022 more
然后跟随数百万行,例如:
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
at $Proxy0.myMethod(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
.......
和:
Caused by: java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
at $Proxy0.myMethod(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at Main.invoke(Main.java:18)
.......
最后打印的行是(在上面的重复序列之后):
Exception: java.lang.WhosebugError thrown from the UncaughtExceptionHandler in thread "main"
我怀疑堆栈跟踪生成机制正在调用代理实例上的一些方法(可能 toString
打印它,或者其他什么),从而一遍又一遍地重复递归(因为每个方法调用代理导致无限递归),但代理方法执行的总计数为 1919(通过在 InvocationHandler.invoke
方法中递增计数器来测量)。
在我的实际用例中,我当然解决了无限递归问题;我很好奇是否有人知道这是错误还是有合理的解释?
Java版本:
java version "1.8.0_65"
Java(TM) SE Runtime Environment (build 1.8.0_65-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.65-b01, mixed mode)
编辑
@JiriTousek 和@AndrewWilliamson 友善地分析了这可能是什么原因。我根据他们的输入实现了模拟:
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.UndeclaredThrowableException;
public class Test {
private static int counter = 0;
public static void main(String[] args) {
proxy();
}
private static void proxy() {
try {
methodInvoke();
} catch (Throwable e) {
throw new UndeclaredThrowableException(e);
}
}
private static void methodInvoke() throws InvocationTargetException {
try {
myMethod();
} catch (Throwable e) {
throw new InvocationTargetException(e);
}
}
private static void myMethod() {
if (counter++ == 5) {
throw new WhosebugError();
}
proxy();
}
}
这导致以下堆栈跟踪:
Exception in thread "main" java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.main(Test.java:9)
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 1 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 2 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 4 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 5 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 7 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 8 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 10 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 11 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 13 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at Test.proxy(Test.java:16)
at Test.myMethod(Test.java:32)
at Test.methodInvoke(Test.java:22)
... 14 more
Caused by: java.lang.reflect.InvocationTargetException
at Test.methodInvoke(Test.java:24)
at Test.proxy(Test.java:14)
... 16 more
Caused by: java.lang.WhosebugError
at Test.myMethod(Test.java:30)
at Test.methodInvoke(Test.java:22)
... 17 more
因此,每个堆栈帧的行号没有增长。
我对此堆栈跟踪的解释是:
- 当最后发生堆栈溢出时,抛出一个
WhosebugError
- 此错误已被
method.invoke()
捕获并转换为InvocationTargetException
(根据 it's javadoc),原因是原始异常 - 由于这个异常是一个已检查的异常,Proxy 不能让它自己掉下来,所以它捕获了它并将它翻译成一个
UndeclaredThrowableException
,再次将前一个作为原因
这样,对于堆栈溢出之前的每个递归级别,您都会得到另外两个 "caused by" 异常及其堆栈跟踪 - 大量输出。至于产量多少,大家猜一猜:
- 根据您的 post ,大约 2000 次调用
- 在每次调用中,堆栈跟踪似乎增长了 5 行
- 为每次调用打印 2 个错误和堆栈跟踪
所以最大的堆栈跟踪将有大约 10000 行,平均堆栈跟踪将有大约 5000 行,所有内容都打印两次(每种异常类型一次),总计约为 2000 * 5000 * 2
= 2000万行.
当相同跟踪的深度超过 1024(默认值)时,打印的堆栈跟踪不是 truncated。这就是为什么最后一个截断的跟踪以 ... 1022 more
结尾,而所有后续跟踪都被完整打印的原因。
可以通过将 MaxJavaStackTraceDepth
JVM 参数设置为所需的值来更改默认值。当我将 Proxy
的原始示例增加到 运行 它与 -XX:MaxJavaStackTraceDepth=8192
时,整个打印的堆栈跟踪下降到大约 12500 行,以:
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at Main1.invoke(Main1.java:16)
... 7003 more
Caused by: java.lang.reflect.UndeclaredThrowableException
at $Proxy0.myMethod(Unknown Source)
... 7007 more
Exception: java.lang.WhosebugError thrown from the UncaughtExceptionHandler in thread "main"