![Spring ResourceLoader
ClassPathXmlApplicationContext
DefaultResourceLoader.
setClassLoader(ClassLoader classLoader)
XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader();
reader.setBeanClassLoader([Class LoaderB here!]);
DefaultListableBeanFactory factory = new DefaultListableBeanFactory(reader);
reader.loadBeanDefinitions([xml resource here!]);
Default: thread context class loader: Thread.currentThread().getContextClassLoader()](https://image.slidesharecdn.com/javaclassloader-130607234315-phpapp02/85/Java-class-loader-29-320.jpg)
![Class.forName(“...HelloWorld")
public class com.carestreamhealth.pas.RemoteWS.utils.HelloWorld {
public com.carestreamhealth.pas.RemoteWS.utils.HelloWorld();
Code:
0: aload_0
1: invokespecial #8 // Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]) throws java.lang.ClassNotFoundException;
Code:
0: ldc #19 // String
com.carestreamhealth.pas.RemoteWS.utils.HelloWorld
2: invokestatic #21 // Method
java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
5: pop
6: return
}](https://image.slidesharecdn.com/javaclassloader-130607234315-phpapp02/85/Java-class-loader-34-320.jpg)
![getClassLoader().loadClass(“..HelloWorld")
public class com.carestreamhealth.pas.RemoteWS.utils.HelloWorld {
public com.carestreamhealth.pas.RemoteWS.utils.HelloWorld();
Code:
0: aload_0
1: invokespecial #8 // Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]) throws java.lang.ClassNotFoundExce
ption, java.lang.InstantiationException, java.lang.IllegalAccessException;
Code:
0: ldc #1 // class
com/carestreamhealth/pas/RemoteWS/utils/HelloWorld
2: invokevirtual #23 // Method
java/lang/Class.getClassLoader:()Ljava/lang/ClassLoader;
5: ldc #29 // String
com.carestreamhealth.pas.RemoteWS.utils.HelloWorld
7: invokevirtual #31 // Method
java/lang/ClassLoader.loadClass:(Ljava/lang/String;)Ljava/lang/Class;
10: pop
11: return
}](https://image.slidesharecdn.com/javaclassloader-130607234315-phpapp02/85/Java-class-loader-35-320.jpg)
![new HelloWorld
public class com.carestreamhealth.pas.RemoteWS.utils.HelloWorld {
public com.carestreamhealth.pas.RemoteWS.utils.HelloWorld();
Code:
0: aload_0
1: invokespecial #8 // Method java/lang/Object."<init>":
()V
4: return
public static void main(java.lang.String[]);
Code:
0: new #1 // class com/carestreamhealth/pas/Re
moteWS/utils/HelloWorld
3: invokespecial #16 // Method "<init>":()V
6: return
}](https://image.slidesharecdn.com/javaclassloader-130607234315-phpapp02/85/Java-class-loader-36-320.jpg)
Java class loader
- 1.
- 2.
- 3.
- 4. When Class.forName() findSystemClass() loadClass() NoClassDefFoundError: compile time Run time
- 5. Agenda JVM classand execute Core ClassLoader and MyClassLoader Tools: jps, jinfo Eclipse-OSGi Maven Spring Dynamic Classes and Method (Reflect, Java 8) Other: MethodNotDef
- 6. Agenda JVM classand execute Core ClassLoader and MyClassLoader Tools: jps, jinfo Eclipse-OSGi Maven Spring Dynamic Classes and Method (Reflect, Java 8) Other: MethodNotDef
- 7.
- 8. Agenda JVM classand execute Core ClassLoader and MyClassLoader Tools: jps, jinfo Eclipse-OSGi Maven Spring Dynamic Classes and Method (Reflect, Java 8) Other: MethodNotDef
- 9. Default class loader sun.misc.Launcher$ExtClassLoader sun.misc.Launcher$AppClassLoader CLASSPATHenvironment variable, -classpath or -cp command line option, Class-Path attribute of Manifest file inside JAR
- 10.
- 11.
- 12.
- 13. Three principles Delegationprinciples Visibility Principle Uniqueness Principle Child ClassLoader can see class loaded by Parent ClassLoad but vice-versa is not true. According to this principle a class loaded by Parent should not be loaded by Child ClassLoader again. DEMO:demo. ExplicitlyLoadClassByExtension
- 14.
- 15. Agenda JVM classand execute Core ClassLoader and MyClassLoader Tools: jps, jinfo Eclipse-OSGi Maven Spring Dynamic Classes and Method (Reflect, Java 8) Other: MethodNotDef
- 16.
- 17.
- 18.
- 19.
- 20. Demo Debug HelloWorldin remote project
- 21. Issue & fix Try to find csdm/client/StartUp.class is exist.
- 22. Agenda JVM classand execute Core ClassLoader and MyClassLoader Tools: jps, jinfo Eclipse-OSGi Maven Spring Dynamic Classes and Method (Reflect, Java 8) Other: MethodNotDef
- 23. Maven System Classloader:Classworlds classloading framework Core Classloader: Plugin Classloaders Custom Classloaders boot the classloader graph: ${maven.home}/boot down the graph contains the core requirements of Maven: ${maven.home}/lib each plugin has its own classloader that is a child of Maven's core classloader plugins/plugin
- 24. Demo: jetty plugin mvn jetty:run @ remote
- 25. a limit onhow long you can make your command line Isolaed Classloader: your classpath isn't really correct. try to escape the confines of an isolated classloader. Manifest-Only JAR:your app may be confused if it finds only our booter.jar there!
- 26. Demo: surefire plugin mvn -Dtest=* test
- 27. Agenda JVM classand execute Core ClassLoader and MyClassLoader Tools: jps, jinfo Eclipse-OSGi Maven Spring Dynamic Classes and Method (Reflect, Java 8) Other: MethodNotDef
- 28. Spring String bean =readerBeanClass() Class clz = classLoader.loadClass(bean) clz .newInstance()
- 29. Spring ResourceLoader ClassPathXmlApplicationContext DefaultResourceLoader. setClassLoader(ClassLoader classLoader) XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(); reader.setBeanClassLoader([Class LoaderB here!]); DefaultListableBeanFactory factory = new DefaultListableBeanFactory(reader); reader.loadBeanDefinitions([xml resource here!]); Default: thread context class loader: Thread.currentThread().getContextClassLoader()
- 30.
- 31. Agenda JVM classand execute Core ClassLoader and MyClassLoader Tools: jps, jinfo Eclipse-OSGi Maven Spring Dynamic Classes and Method (Reflect, Java 8) Other: MethodNotDef
- 32. Agenda JVM classand execute Core ClassLoader and MyClassLoader Tools: jps, jinfo Eclipse-OSGi Maven Spring Dynamic Classes and Method (Reflect, Java 8) Other: MethodNotDef
- 33. Other: MethodNotDef Jarversion
- 34. Class.forName(“...HelloWorld") public class com.carestreamhealth.pas.RemoteWS.utils.HelloWorld{ public com.carestreamhealth.pas.RemoteWS.utils.HelloWorld(); Code: 0: aload_0 1: invokespecial #8 // Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]) throws java.lang.ClassNotFoundException; Code: 0: ldc #19 // String com.carestreamhealth.pas.RemoteWS.utils.HelloWorld 2: invokestatic #21 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class; 5: pop 6: return }
- 35. getClassLoader().loadClass(“..HelloWorld") public class com.carestreamhealth.pas.RemoteWS.utils.HelloWorld{ public com.carestreamhealth.pas.RemoteWS.utils.HelloWorld(); Code: 0: aload_0 1: invokespecial #8 // Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]) throws java.lang.ClassNotFoundExce ption, java.lang.InstantiationException, java.lang.IllegalAccessException; Code: 0: ldc #1 // class com/carestreamhealth/pas/RemoteWS/utils/HelloWorld 2: invokevirtual #23 // Method java/lang/Class.getClassLoader:()Ljava/lang/ClassLoader; 5: ldc #29 // String com.carestreamhealth.pas.RemoteWS.utils.HelloWorld 7: invokevirtual #31 // Method java/lang/ClassLoader.loadClass:(Ljava/lang/String;)Ljava/lang/Class; 10: pop 11: return }
- 36. new HelloWorld public classcom.carestreamhealth.pas.RemoteWS.utils.HelloWorld { public com.carestreamhealth.pas.RemoteWS.utils.HelloWorld(); Code: 0: aload_0 1: invokespecial #8 // Method java/lang/Object."<init>": ()V 4: return public static void main(java.lang.String[]); Code: 0: new #1 // class com/carestreamhealth/pas/Re moteWS/utils/HelloWorld 3: invokespecial #16 // Method "<init>":()V 6: return }
- 37.
- 38. JVM Spec: 5.3Creation and Loading http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-5.html
- 39. Dynamic Classes andMethod (Reflect, Java 8) invokedynamic http://www.slideshare.net/CharlesNutter/jax-2012-invoke-dynamic-keynote
- 40. Java bytecode: Understanding bytecodemakes you a better programmer Example: http://www.ibm.com/developerworks/ibm/library/it-haggar_bytecode/ Java Class: http://en.wikipedia.org/wiki/Java_class_file Java bytecodes: http://en.wikipedia.org/wiki/Java_bytecode_instruction_listings
Editor's Notes
- #13 package demo;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.InputStream;/** * Created with IntelliJ IDEA. * User: 19002850 * Date: 13-5-20 * Time: 下午4:35 * To change this template use File | Settings | File Templates. */public class MyClassLoader extends ClassLoader { private static final int BUFFER_SIZE = 8192; protected synchronized Class loadClass(String className, boolean resolve) throws ClassNotFoundException { log("Loading class: " + className + ", resolve: " + resolve); // 1. is this class already loaded? Class cls = findLoadedClass(className); if (cls != null) { return cls; } // 2. get class file name from class name String clsFile = className.replace('.', '/') + ".class"; // 3. get bytes for class byte[] classBytes = null; try {InputStream in = getResourceAsStream(clsFile); byte[] buffer = new byte[BUFFER_SIZE];ByteArrayOutputStream out = new ByteArrayOutputStream();int n = -1; while ((n = in.read(buffer, 0, BUFFER_SIZE)) != -1) {out.write(buffer, 0, n); }classBytes = out.toByteArray(); } catch (IOException e) { log("ERROR loading class file: " + e); } if (classBytes == null) { throw new ClassNotFoundException("Cannot load class: " + className); } // 4. turn the byte array into a Class try {cls = defineClass(className, classBytes, 0, classBytes.length); if (resolve) {resolveClass(cls); } } catch (SecurityException e) { // loading core java classes such as java.lang.String // is prohibited, throws java.lang.SecurityException. // delegate to parent if not allowed to load classcls = super.loadClass(className, resolve); } return cls; } private static void log(String s) {System.out.println(s); }}
- #14 package demo;import java.util.logging.Level;import java.util.logging.Logger;/** * Java program to demonstrate How ClassLoader works in Java, * in particular about visibility principle of ClassLoader. * * @author Javin Paul */public class ExplicitlyLoadClassByExtension { public static void main(String args[]) { try { //printing ClassLoader of this classSystem.out.println("-------------");System.out.println("ExplicitlyLoadClassByExtension.getClass().getClassLoader() : " + ExplicitlyLoadClassByExtension.class.getClassLoader()); //trying to explicitly load this class again using Extension class loaderSystem.out.println("ExplicitlyLoadClassByExtension.getClass().getClassLoader().getParent() : " + ExplicitlyLoadClassByExtension.class.getClassLoader().getParent());Class.forName("demo.ExplicitlyLoadClassByExtension", true , ExplicitlyLoadClassByExtension.class.getClassLoader().getParent()); } catch (ClassNotFoundException ex) {Logger.getLogger(ExplicitlyLoadClassByExtension.class.getName()).log(Level.SEVERE, null, ex); } }}