1 import java.io.ByteArrayOutputStream;
2 import java.io.File;
3 import java.io.FileInputStream;
4 import java.io.InputStream;
5
6 public class ClassLoaderTest
extends ClassLoader {
7
8 private String classLoaderName;
9 private String fileExtension = ".class"
;
10
11 /**
12 * 默认的情况下，自定义类的加载器会以SystemClassLoader为父类加载器，如果要改变这种机制，调第二种生成方法
13 */
14
15 public ClassLoaderTest(String classLoaderName) {
16 super();
17 this.classLoaderName =
classLoaderName;
18 }
19
20 public ClassLoaderTest(ClassLoader classLoader, String classLoaderName) {
21 super(classLoader);
22 this.classLoaderName =
classLoaderName;
23 }
24
25 /**
26 * 该方法会在底层调用
27 */
28 @Override
29 protected Class<?> findClass(String className)
throws ClassNotFoundException {
30 byte[] data =
this.loadClassData(className);
31 return this.defineClass(className, data, 0
, data.length);
32 }
33
34 // 在该示例里，不会执行该方法，也就是说，由于双亲委托机制，会由应用类加载器加载
35 // 如果加载的类，不在classpath里，意思就是应用类加载器加载不了，才会由此加载器加载
36 private byte[] loadClassData(String name) {
37
38 byte[] data =
null;
39 InputStream is =
null;
40 ByteArrayOutputStream baos =
null;
41
42 try {
43 this.classLoaderName =
this.classLoaderName.replace(".", "/"
);
44
45 is =
new FileInputStream(
new File(name +
this.fileExtension));
46 baos =
new ByteArrayOutputStream();
47
48 int ch = 0
;
49
50 while (-1 != (ch =
is.read())) {
51 baos.write(ch);
52 }
53 data =
baos.toByteArray();
54
55 }
catch (Exception e) {
56 e.printStackTrace();
57 }
finally {
58 try {
59 is.close();
60 baos.close();
61 }
catch (Exception e) {
62 e.printStackTrace();
63 }
64 }
65
66 return data;
67 }
68
69 public static void test(ClassLoader classLoader)
throws Exception {
70 Class<?> clazz = classLoader.loadClass("类名"
);
71 Object o =
clazz.newInstance();
72 System.out.println(o);
73 }
74
75 public static void main(String[] args)
throws Exception {
76 ClassLoaderTest loader1 =
new ClassLoaderTest("loader1"
);
77 test(loader1);
78 }
79
80 }
ps:同一个加载器的命名空间里，同一个类只能被加载一次
命名空间：由所有的父加载器和自己加载器组成的空间
只有由自定义类加载器的类才能被卸载
转载于:https://www.cnblogs.com/billmiao/p/9872212.html
