Thread.currentThread().setContextClassLoader为什么不生效与java.lang.NoClassDefFoundError之Java类加载的Parent first Classloader

 1 #### NoClassDefFoundErrorSimulator.java
 2 package org.ph.javaee.training3;
 3 
 4 import java.net.URL;
 5 import java.net.URLClassLoader;
 6 
 7 import org.ph.javaee.training.util.JavaEETrainingUtil;
 8 
 9 /**
10  * NoClassDefFoundErrorSimulator
11  * @author Pierre-Hugues Charbonneau
12  *
13  */
14 public class NoClassDefFoundErrorSimulator {
15        
16         /**
17          * @param args
18          */
19         public static void main(String[] args) {
20               
21                System.out.println("java.lang.NoClassDefFoundError Simulator - Training 3");
22                System.out.println("Author: Pierre-Hugues Charbonneau");
23                System.out.println("http://javaeesupportpatterns.blogspot.com");
24               
25                // Local variables
26                String currentThreadName = Thread.currentThread().getName();
27                String callerFullClassName = "org.ph.javaee.training3.CallerClassA";
28               
29                // Print current ClassLoader context & Thread
30                System.out.println("\nCurrent Thread name: ‘"+currentThreadName+"‘");
31                System.out.println("Initial ClassLoader chain: "+JavaEETrainingUtil.getCurrentClassloaderDetail());
32               
33                try {
34                        // Location of the application code for our child ClassLoader
35                        URL[] webAppLibURL = new URL[] {new URL("file:caller.jar"),new URL("file:referencer.jar")};
36                       
37                        // Child ClassLoader instance creation              
38                        URLClassLoader childClassLoader = new URLClassLoader(webAppLibURL);
39                       
40                        /*** Application code execution... ***/
41                       
42                        // 1. Change the current Thread ClassLoader to the child ClassLoader
43                        Thread.currentThread().setContextClassLoader(childClassLoader);
44                        System.out.println(">> Thread ‘"+currentThreadName+"‘ Context ClassLoader now changed to ‘"+childClassLoader+"‘");
45                        System.out.println("\nNew ClassLoader chain: "+JavaEETrainingUtil.getCurrentClassloaderDetail());
46                       
47                        // 2. Load the caller Class within the child ClassLoader...
48                        System.out.println(">> Loading ‘"+callerFullClassName+"‘ to child ClassLoader ‘"+childClassLoader+"‘...");
49                        Class<?> callerClass = childClassLoader.loadClass(callerFullClassName);
50                       
51                        // 3. Create a new instance of CallerClassA
52                        Object callerClassInstance = callerClass.newInstance();                    
53                       
54                } catch (Throwable any) {
55                        System.out.println("Throwable: "+any);
56                        any.printStackTrace();
57                }
58               
59                System.out.println("\nSimulator completed!");
60         }
61 }

 1 #### CallerClassA.java
 2 package org.ph.javaee.training3;
 3 
 4 import org.ph.javaee.training3.ReferencingClassA;
 5 
 6 /**
 7  * CallerClassA
 8  * @author Pierre-Hugues Charbonneau
 9  *
10  */
11 public class CallerClassA {
12        
13         private final static Class<CallerClassA> CLAZZ = CallerClassA.class;
14        
15         static {
16                System.out.println("Class loading of "+CLAZZ+" from ClassLoader ‘"+CLAZZ.getClassLoader()+"‘ in progress...");
17         }
18        
19         public CallerClassA() {
20                System.out.println("Creating a new instance of "+CallerClassA.class.getName()+"...");
21               
22                doSomething();
23         }
24        
25         private void doSomething() {
26               
27                // Create a new instance of ReferencingClassA
28                ReferencingClassA referencingClass = new ReferencingClassA();             
29         }
30 }

 1 #### ReferencingClassA.java
 2 package org.ph.javaee.training3;
 3 
 4 /**
 5  * ReferencingClassA
 6  * @author Pierre-Hugues Charbonneau
 7  *
 8  */
 9 public class ReferencingClassA {
10        
11         private final static Class<ReferencingClassA> CLAZZ = ReferencingClassA.class;
12        
13         static {
14                System.out.println("Class loading of "+CLAZZ+" from ClassLoader ‘"+CLAZZ.getClassLoader()+"‘ in progress...");
15         }
16        
17         public ReferencingClassA() {
18                System.out.println("Creating a new instance of "+ReferencingClassA.class.getName()+"...");
19         }
20        
21         public void doSomething() {
22                //nothing to do...
23         }
24 }

 1 ## Baseline (normal execution)
 2 <JDK_HOME>\bin>java -classpath MainProgram.jar org.ph.javaee.training3.NoClassDefFoundErrorSimulator
 3 
 4 java.lang.NoClassDefFoundError Simulator - Training 3
 5 Author: Pierre-Hugues Charbonneau
 6 http://javaeesupportpatterns.blogspot.com
 7 
 8 Current Thread name: ‘main‘
 9 Initial ClassLoader chain:
10 -----------------------------------------------------------------
11 sun.misc.Launcher$ExtClassLoader@17c1e333
12 --- delegation ---
13 sun.misc.Launcher$AppClassLoader@214c4ac9 **Current Thread ‘main‘ Context ClassLoader**
14 -----------------------------------------------------------------
15 
16 >> Thread ‘main‘ Context ClassLoader now changed to ‘java.net.URLClassLoader@6a4d37e5‘
17 
18 New ClassLoader chain:
19 -----------------------------------------------------------------
20 sun.misc.Launcher$ExtClassLoader@17c1e333
21 --- delegation ---
22 sun.misc.Launcher$AppClassLoader@214c4ac9
23 --- delegation ---
24 java.net.URLClassLoader@6a4d37e5 **Current Thread ‘main‘ Context ClassLoader**
25 -----------------------------------------------------------------
26 
27 >> Loading ‘org.ph.javaee.training3.CallerClassA‘ to child ClassLoader ‘java.net.URLClassLoader@6a4d37e5‘...
28 Class loading of class org.ph.javaee.training3.CallerClassA from ClassLoader ‘java.net.URLClassLoader@6a4d37e5‘ in progress...
29 Creating a new instance of org.ph.javaee.training3.CallerClassA...
30 Class loading of class org.ph.javaee.training3.ReferencingClassA from ClassLoader ‘java.net.URLClassLoader@6a4d37e5‘ in progress...
31 Creating a new instance of org.ph.javaee.training3.ReferencingClassA...
32 
33 Simulator completed!

 1 ## Problem reproduction run (static variable initializer failure)
 2 <JDK_HOME>\bin>java -classpath MainProgram.jar;caller.jar org.ph.javaee.training3.NoClassDefFoundErrorSimulator
 3 
 4 java.lang.NoClassDefFoundError Simulator - Training 3
 5 Author: Pierre-Hugues Charbonneau
 6 http://javaeesupportpatterns.blogspot.com
 7 
 8 Current Thread name: ‘main‘
 9 Initial ClassLoader chain:
10 -----------------------------------------------------------------
11 sun.misc.Launcher$ExtClassLoader@17c1e333
12 --- delegation ---
13 sun.misc.Launcher$AppClassLoader@214c4ac9 **Current Thread ‘main‘ Context ClassLoader**
14 -----------------------------------------------------------------
15 
16 >> Thread ‘main‘ Context ClassLoader now changed to ‘java.net.URLClassLoader@6a4d37e5‘
17 
18 New ClassLoader chain:
19 -----------------------------------------------------------------
20 sun.misc.Launcher$ExtClassLoader@17c1e333
21 --- delegation ---
22 sun.misc.Launcher$AppClassLoader@214c4ac9
23 --- delegation ---
24 java.net.URLClassLoader@6a4d37e5 **Current Thread ‘main‘ Context ClassLoader**
25 -----------------------------------------------------------------
26 
27 >> Loading ‘org.ph.javaee.training3.CallerClassA‘ to child ClassLoader ‘java.net.URLClassLoader@6a4d37e5‘...
28 Class loading of class org.ph.javaee.training3.CallerClassA from ClassLoader ‘sun.misc.Launcher$AppClassLoader@214c4ac9‘ in progress...// Caller is loaded from the parent class loader, why???
29 Creating a new instance of org.ph.javaee.training3.CallerClassA...
30 Throwable: java.lang.NoClassDefFoundError: org/ph/javaee/training3/ReferencingClassA
31 java.lang.NoClassDefFoundError: org/ph/javaee/training3/ReferencingClassA
32         at org.ph.javaee.training3.CallerClassA.doSomething(CallerClassA.java:27)
33         at org.ph.javaee.training3.CallerClassA.<init>(CallerClassA.java:21)
34         at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
35         at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
36         at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
37         at java.lang.reflect.Constructor.newInstance(Unknown Source)
38         at java.lang.Class.newInstance0(Unknown Source)
39         at java.lang.Class.newInstance(Unknown Source)
40         at org.ph.javaee.training3.NoClassDefFoundErrorSimulator.main(NoClassDefFoundErrorSimulator.java:51)
41 Caused by: java.lang.ClassNotFoundException: org.ph.javaee.training3.ReferencingClassA
42         at java.net.URLClassLoader$1.run(Unknown Source)
43         at java.net.URLClassLoader$1.run(Unknown Source)
44         at java.security.AccessController.doPrivileged(Native Method)
45         at java.net.URLClassLoader.findClass(Unknown Source)
46         at java.lang.ClassLoader.loadClass(Unknown Source)
47         at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
48         at java.lang.ClassLoader.loadClass(Unknown Source)
49         ... 9 more
50 
51 Simulator completed!