UncaughtExceptionHandler：java未捕获的异常/错误

@(博客文章)[java]

java有一部分异常属于运行时异常，这类异常发生时通过会导致程序发生错误，导致退出。如数据下标过大，内存不足等。

对于这类异常，默认的情况是打印相关的错误stack，然后退出程序。但这对于用户而言十分不友好；另外，有可以发生异常或者错误时不希望程序退出。

此时可以为线程添加一个默认的异常处理器。

主要使用

Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {    public void uncaughtException(Thread thread, Throwable thrown) {    .....    }}

来处理未捕获的异常。也可以使用setUncaughtExceptionHandler，但这只对当前线程生效，default的话默认对所有线程生效。

另注意，Error和Exception 都实现了Throwable，而它们之间没有直接关系

public class UncaughtExceptionHandlerDemo {    private static Logger LOG = LoggerFactory.getLogger(UncaughtExceptionHandlerDemo.class);    public static void main(String[] args) {        setupDefaultUncaughtExceptionHandler();        //NO argument pass to main, so ArrayIndexOutOfBoundsException will occur.        System.out.println(args[1]);    }    public static void setupDefaultUncaughtExceptionHandler() {        Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {                public void uncaughtException(Thread thread, Throwable thrown) {                    try {                        handleUncaughtException(thrown);                    } catch (Error err) {                       // LOG.error("Received error in main thread.. terminating server...", err);                        System.err.println("Received error in main thread.. terminating server..." + err);                        Runtime.getRuntime().exit(-2);                    }catch(Exception e){                        System.err.println("Exception happen. Cause:  " + e.getMessage());                        e.printStackTrace();                    }                }            });    }    public static void handleUncaughtException(Throwable t) throws Exception {        if (t != null && t instanceof Error) {            if (t instanceof OutOfMemoryError) {                try {                    System.err.println("Halting due to Out Of Memory Error..." + Thread.currentThread().getName());                } catch (Throwable err) {                    //Again we don't want to exit because of logging issues.                }                Runtime.getRuntime().halt(-1);            } else {                //Running in daemon mode, we would pass Error to calling thread.                throw (Error) t;            }        }else{            throw (Exception) t;        }    }}