自定义ClassLoader

 

1.  将message.java拷贝到 /users/sunny/test目录下（和nvidiaclassloader类message_class_path指定的路径一致），并编译生成字节码文件(.class)。

message.java:

1 package com.nvidia.util;
2 
3 public class message {
4     public void send() {
5         system.out.println("www.nvidia.com");
6     }
7 }

2.编写自定义classloader类。

nvidiaclassloader.java:

 1 package com.nvidia.util;
 2 
 3 import java.io.bytearrayoutputstream;
 4 import java.io.file;
 5 import java.io.fileinputstream;
 6 import java.io.inputstream;
 7 
 8 public class nvidiaclassloader extends classloader{
 9     private static final string message_class_path = file.separator +"users" + file.separator + "sunny" + file.separator + "test" + file.separator+"message.class";
10     public class<?> loaddata(string classname) throws exception{
11         byte[] data = this.loadclassdata();
12         if(data != null) {
13             return super.defineclass(classname, data, 0, data.length);
14         }
15         return null;
16     }
17     private byte[] loadclassdata() throws exception{
18         inputstream input = null;
19         bytearrayoutputstream bos = null;
20         byte data[] = null;
21         try {
22             bos = new bytearrayoutputstream();
23             input = new fileinputstream(new file(message_class_path));
24             input.transferto(bos);
25             data = bos.tobytearray();
26         } catch (exception e) {
27             e.printstacktrace();
28         }finally {
29             if(input != null) {
30                 input.close();
31             }
32             if(bos != null) {
33                 bos.close();
34             }
35         }
36         return data;
37     }
38 }

 

3.测试类。

javareflectdemo:

 1 package com.nvidia.demo;
 2 
 3 import com.nvidia.util.nvidiaclassloader;
 4 import java.lang.reflect.method;
 5 
 6 public class javareflectdemo {
 7     public static void main(string[] args) throws exception {
 8         nvidiaclassloader classloader = new nvidiaclassloader();
 9         class<?> cls = classloader.loaddata("com.nvidia.util.message");
10         //system.out.println(cls);
11         object object = cls.getdeclaredconstructor().newinstance();
12         method method = cls.getdeclaredmethod("send");
13         method.invoke(object);
14         system.out.println(cls.getclassloader());
15         system.out.println(cls.getclassloader().getparent());
16         system.out.println(cls.getclassloader().getparent().getparent());
17     }
18 }

运行结果：

www.nvidia.com
com.nvidia.util.nvidiaclassloader@5451c3a8
jdk.internal.loader.classloaders$appclassloader@55054057
jdk.internal.loader.classloaders$platformclassloader@2c7b84de