JavaSE---Class.getResource与ClassLoader.getResource

 

package com.an.classloadertest;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;

/**
 * @author apy
 * @description
 * @date 2022/3/9 16:44
 */
public class TestMain {

    private String name;
    private String job;

    public String getJob() {
        return job;
    }

    public String getName() {
        return name;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "TestMain{" +
                "name='" + name + '\'' +
                ", job='" + job + '\'' +
                '}';
    }

    public static void main(String[] args) throws IOException, IllegalAccessException, InstantiationException, ClassNotFoundException {

        // TestMain.class.getResource("/") 与 testMain.getClass().getClassLoader().getResource("") 路径一致

//        test();

//        classTest();

//        classLoaderTest1();

//        classLoaderTest();

//        scanPackage();

    }

    private static void scanPackage() throws IOException, ClassNotFoundException, IllegalAccessException, InstantiationException {

        TestMain testMain = new TestMain();

        List<File> list = new ArrayList<>();

        final String scanPackage = "com/an/classloadertest";

        Enumeration<URL> urlEnumeration = testMain.getClass().getClassLoader().getResources(scanPackage);
        while (urlEnumeration.hasMoreElements()){
            URL url = urlEnumeration.nextElement();
            File file = new File(url.getFile());
            list.add(file);
        }

        String[] resources = list.stream().findFirst().get().list();
        for (String resource : resources){

            if (resource.equals("TestMain.class")){
                Class<?> testClass = Class.forName(scanPackage.replace("/", ".") + "." + resource.replace(".class", ""));
                Object newInstance = testClass.newInstance();
                System.out.println(newInstance); // TestMain{name='null', job='null'}
            }
        }



    }

    private static void classLoaderTest1() {

        TestMain testMain = new TestMain();

        System.out.println(testMain.getClass().getClassLoader().getResource(""));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/

        System.out.println(testMain.getClass().getClassLoader().getResource("1.properties"));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/1.properties

        System.out.println(testMain.getClass().getClassLoader().getResource("com/an/classloadertest/2.properties"));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/com/an/classloadertest/2.properties

        System.out.println(testMain.getClass().getClassLoader().getResource("com/an/classloadertest/sub/3.properties"));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/com/an/classloadertest/sub/3.properties

    }

    private static void classLoaderTest() {

        TestMain testMain = new TestMain();

        System.out.println(testMain.getClass());
        //class com.an.classloadertest.TestMain

        System.out.println(testMain.getClass().getClassLoader());
        //sun.misc.Launcher$AppClassLoader@18b4aac2

        System.out.println(testMain.getClass().getClassLoader().getResource(""));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/

        System.out.println(testMain.getClass().getClassLoader().getResource("/"));
        //null
    }

    private static void classTest() {

        System.out.println(TestMain.class.getResource(""));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/com/an/classloadertest/

        System.out.println(TestMain.class.getResource("/"));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/

        System.out.println(TestMain.class.getResource("2.properties"));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/com/an/classloadertest/2.properties

        System.out.println(TestMain.class.getResource("sub/3.properties"));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/com/an/classloadertest/sub/3.properties

        System.out.println(TestMain.class.getResource("/1.properties"));
        //file:/Users/an/IdeaProjects/demo/javase/target/classes/1.properties
    }

    private static void test() {

        System.out.println(TestMain.class.getResource(""));
        // file:/Users/an/IdeaProjects/demo/javase/target/classes/com/an/classloadertest/

        System.out.println(TestMain.class.getResource("/"));
        // file:/Users/an/IdeaProjects/demo/javase/target/classes/

    }

}