Log4j从异常堆栈中获取类、方法、行数演示

Log4j从异常堆栈中获取类、方法、行数演示

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好奇Log4j格式化日志时，上述信息获取方式。 跟踪代码，发现了其利用异常实现的，下面是简单例子:

  1. package com.billstudy.test;
  3. import java.lang.reflect.Method;
  5. /**
  6.  * Test exception stack infomation analysis 
  7.  * @author LiBiao - Bill
  8.  * @since V1.0 2016年4月15日 - 下午5:48:35
  9.  */
  10. @SuppressWarnings({ "unchecked", "rawtypes" })
  11. public class StackDemo {
  13. 	private static Method getStackTraceMethod;
  14. 	private static Method getClassNameMethod;
  15. 	private static Method getMethodNameMethod;
  16. 	private static Method getFileNameMethod;
  17. 	private static Method getLineNumberMethod;
  19. 	static {
  20. 		Class[] noArgs = null;
  21. 		try {
  22. 			getStackTraceMethod = Throwable.class.getMethod("getStackTrace", noArgs);
  23. 			Class stackTraceElementClass = Class.forName("java.lang.StackTraceElement");
  24. 			getClassNameMethod = stackTraceElementClass.getMethod("getClassName", noArgs);
  25. 			getMethodNameMethod = stackTraceElementClass.getMethod("getMethodName", noArgs);
  26. 			getFileNameMethod = stackTraceElementClass.getMethod("getFileName", noArgs);
  27. 			getLineNumberMethod = stackTraceElementClass.getMethod("getLineNumber", noArgs);
  28. 		} catch (Exception e) {
  29. 			e.printStackTrace();
  30. 		}
  31. 	}
  33. 	/**
  34. 	 * Obtain relevant information from the exception stack
  35. 	 * @author LiBiao - Bill
  36. 	 * @since V1.0 2016年4月15日 - 下午6:14:33
  37. 	 * @param e
  38. 	 * @param className
  39. 	 */
  40. 	private static void analysisException(Exception e, String className) {
  41. 		Object[] noArgs = null;
  42. 		try {
  43. 			Object[] elements =  (Object[]) getStackTraceMethod.invoke(e,noArgs);
  44. 			for (int i = 0; i < elements.length; i++) {
  45. 				Object element = elements[i];
  46. 				String clazz = (String) getClassNameMethod.invoke(element, noArgs);
  47. 				// find 
  48. 				if (className.equals(clazz)) {
  49. 					String method = (String) getMethodNameMethod.invoke(element, noArgs);
  50. 					int line = (Integer) getLineNumberMethod.invoke(element, noArgs);
  51. 					String fileName = (String) getFileNameMethod.invoke(element, noArgs);
  52. 					String result = String.format(
  53. 							  "class:%s \r\n "
  54. 							+ "method:%s \r\n "
  55. 							+ "line:%s \r\n "
  56. 							+ "fileName:%s \r\n errorMsg:%s", clazz,method,line,fileName,e.getMessage());
  57. 					System.out.println(result);
  58. 					break;
  59. 				}
  60. 			}
  61. 		} catch (Exception ex) {
  62. 			ex.printStackTrace();
  63. 		}
  64. 	}
  66. 	public static void main(String[] args) {
  67. 		String findClassName = "com.billstudy.test.StackDemo$B";
  68. 		try {
  69. 			A a = new A();
  70. 			a.test();
  71. 		} catch (Exception e) {
  72. 			//e.printStackTrace();
  73. 			analysisException(e, findClassName);
  74. 		}
  75. 		// a.nullException();
  76. 	}
  78. 	
  79. 	
  80. 	public static class A {
  81. 		private B b = new B();
  83. 		public void test() {
  84. 			b.test();
  85. 		}
  87. 		public void nullException() {
  88. 			String target = null;
  89. 			target.intern();
  90. 		}
  91. 	}
  93. 	public static class B {
  94. 		private C c = new C();
  96. 		public void test() {
  97. 			c.test();
  98. 		}
  99. 	}
  101. 	public static class C {
  102. 		public void test() {
  103. 			throw new RuntimeException("别问我为啥，就是想抛个异常 ~");
  104. 		}
  105. 	}
  106. }

输出：
  1. class:com.billstudy.test.StackDemo$B 
  2.  method:test 
  3.  line:97 
  4.  fileName:StackDemo.java 
  5.  errorMsg:别问我为啥，就是想抛个异常 ~

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