This article mainly introduces the java custom ClassLoader to load the specified class file operation, which has a good reference value, and I hope it will be helpful to everyone. Let's follow the editor to take a look
You can customize a class loader by inheriting ClassLoader and overriding the findClass method. What is a class loader and the loading process and order of the class loader will be discussed next time. Here is a small demo
First define a class, such as MyTest, and compile it into a class file, and then put it under a specified folder. The last few layers of the folder are its package name. Here I put the compiled class in: /Users/allen/Desktop/cn/lijie/MyTest.class
package cn.lijie;
public class MyTest {
public void show() {
System.out.println("show test!");
}
}
自定义的类加载器：
`public` `class` `MyClassLoader` `extends` `ClassLoader {
`
`@Override`
`protected` `Class<?> findClass(String name) {
`
`String myPath =` `"[file:///Users/allen/Desktop/](file:///Users/allen/Desktop/)"` `+ name.replace(``"."``,``"/"``) +` `".class"``;`
`System.out.println(myPath);`
`byte``[] cLassBytes =` `null``;`
`Path path =` `null``;`
`try` `{
`
`path = Paths.get(``new` `URI(myPath));`
`cLassBytes = Files.readAllBytes(path);`
`}` `catch` `(IOException | URISyntaxException e) {
`
`e.printStackTrace();`
`}`
`Class clazz = defineClass(name, cLassBytes,` `0``, cLassBytes.length);`
`return` `clazz;`
`}`
`}`
The main function of the test:
public class MainClass {
public static void main(String[] args) throws ClassNotFoundException {
MyClassLoader loader = new MyClassLoader();
Class<?> aClass = loader.findClass("cn.lijie.MyTest");
try {
Object obj = aClass.newInstance();
Method method = aClass.getMethod("show");
method.invoke(obj);
} catch (Exception e) {
e.printStackTrace();
}
}
}
Execute the main function and call the show method of the external class:
Supplement: java remote load class file
1. Create java file on win and compile
2. Upload to remote server
3. Preparation for writing java code
:
introducing the jar package ganymed-ssh2-262.jar
-
1. To load an external class, define your own class loader
-
2. Use memory streaming
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import ch.ethz.ssh2.Connection;
import ch.ethz.ssh2.SFTPInputStream;
import ch.ethz.ssh2.SFTPv3Client;
public class Fs{
public static void main(String[] args) throws Exception {
OwnClassLoader ocl = new OwnClassLoader();
String ip,user,password;
ip = "120.34.168.80";//自己的远程ip
user = "root";//username
password = "123456";//password
ocl.login(ip, user, password);
Object obj = ocl.loadeOthClass("/opt/4/tt.class");//class文件路径
System.out.println(obj);
Class c = obj.getClass();
Field f = c.getDeclaredField("age");
f.setAccessible(true);
System.out.println("age:"+f.get(obj));
}
}
//自定义类加载器
class OwnClassLoader extends ClassLoader{
private Connection conn = null;
//初始化链接
public Connection login(String ip,String user,String password){
Connection conn = null;
try {
//也可以new Connection(ip, port)创建对象,默认22
conn = new Connection(ip);
//连接远程服务
conn.connect();
//使用用户名和密码登录
conn.authenticateWithPassword(user, password);
this.conn = conn;
return conn;
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
//返回远程实例
public Object loadeOthClass(String url) throws Exception{
if(null==conn)
throw new Exception("请初始化链接");
SFTPv3Client sc = new SFTPv3Client(conn);//创建ssh客户端连接
InputStream is = new SFTPInputStream(sc.openFileRO(url));//创建输入流
byte[] b = this.readClassFile(is);
Class<?> c = super.defineClass(b, 0, b.length);//定义class
return c.newInstance();//创建实例
}
//读取远程class文件
private byte[] readClassFile(InputStream is){
byte[] b = new byte[1024];
int len;
ByteArrayOutputStream bos = null;
try {
bos = new ByteArrayOutputStream();//内存流输出
while((len=is.read(b))!=-1){
bos.write(b, 0, len);
}
b = bos.toByteArray();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
try {
if(is!=null)
is.close();
if(bos!=null)
bos.close();
} catch (Exception e2) {
// TODO: handle exception
}
}
return b;
}
}
Output result:
The above is personal experience, I hope to give you a reference, and I hope you can support the editor. If there are mistakes or not fully considered, please feel free to enlighten me.