fix the issue when the woven code is still running and throw NullPointerException after executing the stop command. #1094

spy/src/main/java/java/arthas/Spy.java

@@ -8,7 +8,12 @@ import java.lang.reflect.Method;
  * Created by vlinux on 15/8/23.
  */
 public class Spy {
-
+    public static final String ON_BEFORE = "methodOnBegin";
+    public static final String ON_RETURN = "methodOnReturnEnd";
+    public static final String ON_THROWS = "methodOnThrowingEnd";
+    public static final String BEFORE_INVOKE = "methodOnInvokeBeforeTracing";
+    public static final String AFTER_INVOKE = "methodOnInvokeAfterTracing";
+    public static final String THROW_INVOKE = "methodOnInvokeThrowTracing";
 
     // -- 各种Advice的钩子引用 --
     public static volatile Method ON_BEFORE_METHOD;
@@ -53,13 +58,7 @@ public class Spy {
      * to avoid classloader leak.
      */
     public static void destroy() {
-        CLASSLOADER = null;
-        ON_BEFORE_METHOD = null;
-        ON_RETURN_METHOD = null;
-        ON_THROWS_METHOD = null;
-        BEFORE_INVOKING_METHOD = null;
-        AFTER_INVOKING_METHOD = null;
-        THROW_INVOKING_METHOD = null;
+        initEmptySpy();
         // clear the reference to ArthasClassLoader in AgentLauncher
         if (AGENT_RESET_METHOD != null) {
             try {
@@ -71,4 +70,62 @@ public class Spy {
         AGENT_RESET_METHOD = null;
     }
 
+    private static void initEmptySpy() {
+        try {
+            Class<?> adviceWeaverClass = Spy.class;
+            Method onBefore = adviceWeaverClass.getMethod(Spy.ON_BEFORE, int.class, ClassLoader.class, String.class,
+                    String.class, String.class, Object.class, Object[].class);
+            Method onReturn = adviceWeaverClass.getMethod(Spy.ON_RETURN, Object.class);
+            Method onThrows = adviceWeaverClass.getMethod(Spy.ON_THROWS, Throwable.class);
+            Method beforeInvoke = adviceWeaverClass.getMethod(Spy.BEFORE_INVOKE, int.class, String.class, String.class,
+                    String.class, int.class);
+            Method afterInvoke = adviceWeaverClass.getMethod(Spy.AFTER_INVOKE, int.class, String.class, String.class,
+                    String.class, int.class);
+            Method throwInvoke = adviceWeaverClass.getMethod(Spy.THROW_INVOKE, int.class, String.class, String.class,
+                    String.class, int.class);
+            Spy.init(null, onBefore, onReturn, onThrows, beforeInvoke, afterInvoke, throwInvoke);
+        } catch (Exception e) {
+        }
+    }
+
+    /**
+     * empty method
+     * 
+     * @see com.taobao.arthas.core.advisor.AdviceWeaver#methodOnBegin(int,
+     *      ClassLoader, String, String, String, Object, Object[])
+     * @param adviceId
+     * @param loader
+     * @param className
+     * @param methodName
+     * @param methodDesc
+     * @param target
+     * @param args
+     */
+    public static void methodOnBegin(int adviceId, ClassLoader loader, String className, String methodName,
+            String methodDesc, Object target, Object[] args) {
+    }
+
+    /**
+     * empty method
+     * 
+     * @see com.taobao.arthas.core.advisor.AdviceWeaver#methodOnReturnEnd(Object)
+     * @param returnObject
+     */
+    public static void methodOnReturnEnd(Object returnObject) {
+    }
+
+    public static void methodOnThrowingEnd(Throwable throwable) {
+    }
+
+    public static void methodOnInvokeBeforeTracing(int adviceId, String owner, String name, String desc,
+            int lineNumber) {
+    }
+
+    public static void methodOnInvokeAfterTracing(int adviceId, String owner, String name, String desc,
+            int lineNumber) {
+    }
+
+    public static void methodOnInvokeThrowTracing(int adviceId, String owner, String name, String desc,
+            int lineNumber) {
+    }
 }