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![APIs on ClassLoader
• Get parent class loader.getParent()
• Load the class by given name, return a class instance.loadClass(String name)
• Find the class by given name, return a class instancefindClass(String name)
• Find the loaded class by given name
findLoadedClass(String
name)
• Generate class instance from its binary representation
• Final function
defineClass(Strign, byte[]
b, int off, int len)
• Link given classresolveClass(Class<?> c)](https://image.slidesharecdn.com/letstalkaboutjavaclassloader-151106051747-lva1-app6891/85/Let-s-talk-about-java-class-loader-8-320.jpg)
![APIs on ClassLoader
• Get parent class loader.getParent()
• Load the class by given name, return a class instance.loadClass(String name)
• Find the class by given name, return a class instancefindClass(String name)
• Find the loaded class by given name
findLoadedClass(String
name)
• Generate class instance from its binary representation
• Final function
defineClass(Strign, byte[]
b, int off, int len)
• Link given classresolveClass(Class<?> c)](https://image.slidesharecdn.com/letstalkaboutjavaclassloader-151106051747-lva1-app6891/75/Let-s-talk-about-java-class-loader-8-2048.jpg)
Uploaded byYongqiang Li
Let's talk about java class loader
This document discusses Java classloaders. It defines a classloader as an object responsible for loading classes into the Java Virtual Machine (JVM). Without a classloader, no classes can be loaded or run in the JVM. It describes the parent-child structure of classloaders, with the bootstrap classloader at the top loading core Java libraries and having no parent. It provides examples of different classloaders like the extensions classloader and system classloader, as well as custom classloaders. It also lists some common classloader APIs and discusses how classloaders load and resolve classes. It raises questions about classloader precedence when multiple classloaders load the same class and mentions "Jar Hell" issues with classpath conflicts. OSGi classloading
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Let's talk about java class loader
- 1.
- 2. Previously… (about 3years ago) Let’s talk about JNI Let’s talk about Java Class File
- 4. What’s ClassLoader? Aclass loader is an object that is responsible for loading classes. Without classloader, no class can be loaded and run in JVM. Classes are loaded into JVM and by demand (lazy initialization) Each ClassLoader has a parent, except the bootstrap one.
- 5. Parent-Child Structure of ClassLoader •LoadJava Core libraries (jre/lib/rt.jar) •Implemented by C++ •not derived from java.lang.ClassLoader •No parent Bootstrap Class Loader •Load Java Extension (jre/ext/*.jar) Extensions Class Loader •Load libraries defined in CLASSPATH System Class Loader •Custom class loader derived from java.lang.ClassLoader Custom Class Loader
- 6. Bootstrap class loader Extensions class loader Systemclass loader Custom class loader1 Custom class loader2 Default Loaders Custom class loader3
- 8. APIs on ClassLoader •Get parent class loader.getParent() • Load the class by given name, return a class instance.loadClass(String name) • Find the class by given name, return a class instancefindClass(String name) • Find the loaded class by given name findLoadedClass(String name) • Generate class instance from its binary representation • Final function defineClass(Strign, byte[] b, int off, int len) • Link given classresolveClass(Class<?> c)
- 9.
- 10. Function of findClass(in URLClassLoader)
- 11.
- 13. Q: If urlClassLoader3loads class A first, will the output be changed?
- 14. More… “Jar Hell” PackageA Package B org.yli.test 0.1 org.yli.test 0.2 Package C Q: Any Solution?
- 15.
- 16. References Java ClassLoaderon Wiki Execution on Java SE specification