Java 输出 printStackTrace 堆栈信息

import java.io.PrintWriter;import java.io.StringWriter;public class MainDemo {    private static String USER_NAME;    public static void main(String[] args) {        try {            // 空指针异常            System.out.println(USER_NAME.equals(""));        } catch (Exception ex) {            ex.printStackTrace();            System.out.println("----------------------------");            Exception exception = ex;            StringWriter writer = new StringWriter();            exception.printStackTrace(new PrintWriter(writer));            System.out.println(writer.getBuffer().toString());        }    }}

输出结果:

java.lang.NullPointerExceptionat MainDemo.main(MainDemo.java:9)----------------------------java.lang.NullPointerExceptionat MainDemo.main(MainDemo.java:9)