【0】README

0.1）本文主要對(duì)類加載器進(jìn)行分析，且 URLClassLoader是 ClassLoader的子類；

0.2）關(guān)于如何設(shè)置類加載器的加載路徑，參見?對(duì)servlet容器的補(bǔ)充

【1】URLClassLoader類加載器

1.1）URLClassLoader的一種加載方式

package com.tomcat.classloader;import java.io.File; import java.lang.reflect.Constructor; import java.lang.reflect.Method; import java.net.URL; import java.net.URLClassLoader;public class URLClassLoaderTest {public final static String dir = System.getProperty("user.dir") + File.separator + "src" + File.separator;public static void main(String[] args) throws Exception {// Getting the jar URL which contains target classURL[] classLoaderUrls = new URL[]{new URL("file:" + dir)};// Create a new URLClassLoader URLClassLoader urlClassLoader = new URLClassLoader(classLoaderUrls);// Load the target classClass<?> beanClass = urlClassLoader.loadClass("com.tomcat.test.Bean");// Create a new instance from the loaded classConstructor<?> constructor = beanClass.getConstructor();Object beanObj = constructor.newInstance();// Getting a method from the loaded class and invoke itMethod method = beanClass.getMethod("sayHello");method.invoke(beanObj);} } package com.tomcat.test;public class Bean {public void sayHello() {System.out.println("Hello from loaded Bean class for test!!!");} }

1.2）URLClassLoader的另一種加載方式

package com.tomcat.classloader;import java.io.File; import java.lang.reflect.Constructor; import java.lang.reflect.Method; import java.net.MalformedURLException; import java.net.URL; import java.net.URLClassLoader;public class URLClassLoaderTest {public final static String dir = System.getProperty("user.dir") + File.separator + "webroot" + File.separator;public static void main(String[] args) { try {File file = new File(dir);URL url = file.toURI().toURL(); // attend this lineURL[] urls = new URL[]{url};URLClassLoader loader = new URLClassLoader(urls, null, null); System.out.println("test = " + loader.getURLs()[0].toString());Class<?> beanClass = loader.loadClass("servlet.Bean");Object obj = beanClass.newInstance();Method method = beanClass.getMethod("sayHello");method.invoke(obj);} catch (Exception e) {e.printStackTrace();} } }

【2】ClassLoader類加載器的加載方式

package com.tomcat.test;import java.lang.reflect.Constructor; import java.lang.reflect.Method;public class ClassLoaderTest { // 第一種加載類的方式public static void main1(String[] args) throws Exception { Class<?> newClass = Class.forName("com.tomcat.classloader.Bean");Constructor constructor = newClass.getConstructor();Object obj = constructor.newInstance();Method method = newClass.getMethod("sayHello");method.invoke(obj);}// 第二種加載類的方式public static void main(String[] args) throws Exception { ClassLoader loader = Thread.currentThread().getContextClassLoader();Class<?> newClass = loader.loadClass("com.tomcat.classloader.Bean");Constructor constructor = newClass.getConstructor();Object obj = constructor.newInstance();Method method = newClass.getMethod("sayHello");method.invoke(obj);} }

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