java加载外部class/jar包class文件，测试并记录URL类所支持的协议

ClassLoader加载外部类

在桌面a文件夹创建了A.java，通过cmd命令在当前a目录下编译成A.class文件，然后运行如下代码：

public static void main(String[] args) throws Exception {
        File file = new File("C:\\Users\\pactera\\Desktop\\a");
        URL[] urls = {file.toURI().toURL()};
        URLClassLoader urlClassLoader = new URLClassLoader(urls);
        Class<?> a = urlClassLoader.loadClass("A");
        System.out.println(a);
    }

输出结果：

ClassLoader加载外部jar

在本地maven仓库中随便找了个jar
运行如下代码：

注意：URL中 -------------- jar协议 前缀格式固定为jar:file:/

 public static void main(String[] args) throws Exception {
//        方式一
        File file = new File("E:\\repository\\commons-io\\commons-io\\2.2\\commons-io-2.2.jar");
        URL[] urls1 = {file.toURI().toURL()};
        URLClassLoader urlClassLoader1 = new URLClassLoader(urls1);
        Class<?> aClass1 = urlClassLoader1.loadClass("org.apache.commons.io.IOUtils");
        System.out.println(aClass1);

//        方式二
        URL url = new URL("jar:file:/E:/repository/commons-io/commons-io/2.2/commons-io-2.2.jar"+"!/");
        URL[] urls = {url};
        URLClassLoader urlClassLoader = new URLClassLoader(urls);
        Class<?> ioUtils = urlClassLoader.loadClass("org.apache.commons.io.IOUtils");
        System.out.println(ioUtils);
//        方式三
        URLClassLoader systemClassLoader = (URLClassLoader) ClassLoader.getSystemClassLoader();
        Method addURL = URLClassLoader.class.getDeclaredMethod("addURL", URL.class);
        addURL.setAccessible(true);
        addURL.invoke(systemClassLoader, url);
        Class<?> aClass = systemClassLoader.loadClass("org.apache.commons.io.IOUtils");
        System.out.println(aClass);
    }

URL类支持如下协议

• http，https，ftp，mailto，file，jar，netdoc
  测试如下：

package com.example.demo.test;

import java.net.MalformedURLException;
import java.net.URL;

public class TestURLProtocol {

    public static void main(String[] args) {
        String host = "www.baidu.com";
        String file = "/index.html";
        
        String[] schames = {"http", "https", "ftp", "mailto", "telnet", "file", "ldap", "gopher",
                 "jdbc", "rmi", "jndi", "jar", "doc", "netdoc", "nfs", "verbatim", "finger", "daytime",
                "systemresource","webService","redis","zookeeper","rest","thrift","dubbo"};
        for (int i= 0; i < schames.length; i++) {
            try {
                URL url = new URL(schames[i], host, file);
                System.out.println(schames[i] + " is supported");
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                System.out.println(schames[i] + " is not supported");
            }
        }

    }
}