Java implementiert einen benutzerdefinierten Klassenlader

* <blockquote><pre class="brush:php;toolbar:false">
 *     class NetworkClassLoader extends ClassLoader {
 *         String host;
 *         int port;
 *
 *         public Class findClass(String name) {
 *             byte[] b = loadClassData(name);
 *             return defineClass(name, b, 0, b.length);
 *         }
 *
 *         private byte[] loadClassData(String name) {
 *             // load the class data from the connection
 *              . . .
 *         }
 *     }
 * 

package reflect;
 
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
 
public class MyClassLoader extends ClassLoader{
 
    // 用于保存加载的文件的大小
    private int classSize; 
    // 新增的类加载路径
    private static List<String> paths = new ArrayList<>();
 
    static {
        paths.add("D:\\Users\\jeff.chan\\Desktop\\");
    }
    // 默认会将app类加载器做为该类加载器的父加载器
    public MyClassLoader() {
    }
 
    public MyClassLoader(ClassLoader parent) {
        super(parent);
    }
 
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        byte[] b = loadBinaryData(name);
        // 打印执行标记
        System.out.println("use custom classloader...");
        return defineClass(name, b,0, classSize);
    }
 
    public byte[] loadBinaryData(String name) throws ClassNotFoundException{
        String pathName = name.replaceAll("\\.", "/");
        File file = null;
        for (String path : paths) {
            file = new File(path+pathName+".class");
            if(file.exists() && file.isFile()){
                break;
            }
        }
        if(file==null || !file.isFile()){
            throw  new ClassNotFoundException();
        }
        // 读取文件的二进制信息
        try (InputStream in = new FileInputStream(file)){
            // 一般这个大小够了，这里是为了方便读取
            // 文件的内容，所以一次性读入，并且将大小返回
            // 用于defineClass
            byte[] b = new byte[1024 * 1024 * 10];
            classSize = in.read(b);
            return b;
        }catch (IOException ioException){
            ;
        }
        return null;
    }
}

D:\\Users\\jeff.chan\\Desktop\\

package reflect;
 
 
public class Person {
 
    private String name;
    private String age;
 
    public Person() {
    }
 
    public Person(String name, String age) {
        this.name = name;
        this.age = age;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getAge() {
        return age;
    }
 
    public void setAge(String age) {
        this.age = age;
    }
 
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

package reflect;
 
public class Client {
 
    public static void main(String[] args) throws Exception {
        MyClassLoader classLoader = new MyClassLoader();
        Class<?> aClass = classLoader.loadClass("reflect.Person");
        System.out.println(aClass);
        System.out.println(aClass.getClassLoader());
    }
}