1
static {
2
    try {
3
        // 通过反射获取
4
        Field f = Unsafe.class.getDeclaredField("theUnsafe");
5
        // private 2 public
6
        f.setAccessible(true);
7
        // static
8
        unsafe = (Unsafe) f.get(null);
9
    }catch (Exception e){
10
        e.printStackTrace();
11
    }
12
}
13

14
// 修改String 的 数值
15
public static void modify(String src, String to) {
16
    try {
17
        Field value = setAccessible(String.class.getDeclaredField("value"));
18
        set(src, value, value.get(to));
19
    } catch (Exception e) {
20
        throw new RuntimeException(e);
21
    }
22
}
23

24
// unsafe
25
public static void set(Object obj, Field field, Object value) throws Exception {
26
    unsafe.putObject(obj, unsafe.objectFieldOffset(field), value);
27
}
28

29

30
public static <T extends AccessibleObject> T setAccessible(T t) {
31
    t.setAccessible(true);
32
    return t;
33
}

1
public static sun.misc.Unsafe unsafe = null;
2

3
public static void main(String[] args) throws Throwable {
4
    ServerSocket ss = new ServerSocket(1145);
5

6
    System.setSecurityManager(new SecurityManager() {
7
        // 必须重写
8
        @Override
9
        public void checkPermission(Permission perm) {}
10

11
        @Override
12
        public void checkConnect(String host, int port) {
13
            modify(host,"172.17.209.50"); // 修改内容
14
            System.out.println("尝试连接 "+host + " " + port);
15
        }
16

17
        @Override
18
        public void checkConnect(String host, int port, Object context) {
19
            checkConnect(host,port);
20
        }
21

22
    });
23
    Socket socket = new Socket("127.0.0.1",1145);
24

25
    socket.close();
26
    System.out.println("end");
27
}

1
synchronized void load0(Class<?> fromClass, String filename) {
2
    SecurityManager security = System.getSecurityManager();
3
    if (security != null) {
4
        security.checkLink(filename);
5
    }
6
    if (!(new File(filename).isAbsolute())) {
7
        throw new UnsatisfiedLinkError(
8
            "Expecting an absolute path of the library: " + filename);
9
    }
10
    ClassLoader.loadLibrary(fromClass, filename, true);
11
}

1
public static void main(String[] args) throws Throwable {
2

3
    System.setSecurityManager(new SecurityManager() {
4
        // 必须重写
5
        @Override
6
        public void checkPermission(Permission perm) {}
7

8
        @Override
9
        public void checkLink(String lib) {
10
            if (check(lib)) // 写你对加载的库进行判断
11
            {
12
                // 修改路径
13
                modify(lib,"redirect_libPath");
14
            }
15
        }
16
    });
17

18
    new Scanner(System.in).next();
19
    System.out.println("end");
20
}

1
public static void main(String[] args) throws Throwable {
2
    System.setSecurityManager(new SecurityManager() {
3
        // 必须重写
4
        @Override
5
        public void checkPermission(Permission perm) {
6
            if (perm.getName().equals("setSecurityManager")) throw new RuntimeException("禁止修改 SecurityManager ");
7
        }
8
    });
9
    System.out.println("设置安全管理器成功");
10

11
    // 进行第二次设置
12
    System.setSecurityManager(new SecurityManager());
13
    System.out.println("end");
14
}

1
设置安全管理器成功
2
Exception in thread "main" java.lang.RuntimeException: 禁止修改 SecurityManager
3
  at test.BeautifulMain$1.checkPermission(BeautifulMain.java:21)
4
  at java.lang.System.setSecurityManager0(System.java:300)
5
  at java.lang.System.setSecurityManager(System.java:291)
6
  at test.BeautifulMain.main(BeautifulMain.java:28)