Java SecurityManager checkListen（）方法与示例

SecurityManager类的checkListen()方法 (SecurityManager Class checkListen() method)

checkListen() method is available in java.lang package.
checkListen()方法在java.lang包中可用。
checkListen() method invokes checkPermission with the given SocketPermission("localhost:"+port_no,"listen") when the given argument value is not equal to 0 otherwise it invokes checkPermission with the SocketPermission("localhost:1024-","listen") when the given argument value equal to 0.
当给定参数值不等于0时， checkListen()方法使用给定的SocketPermission(“ localhost：” + port_no，“ listen”)调用checkPermission；否则，使用SocketPermission(“ localhost：1024-”，“ listen”)调用checkPermission )，则给定参数值等于0。
checkListen() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
checkListen()方法是一种非静态方法，只能通过类对象访问，如果尝试使用类名称访问该方法，则会收到错误消息。
checkListen() method may throw an exception at the time of establishing the connection.
建立连接时， checkListen()方法可能会引发异常。

SecurityException – This exception may throw when the calling thread is not allowed to listen (i.e. it does not wait for a connection request) on the given port.
SecurityException-如果不允许调用线程在给定端口上侦听(即，它不等待连接请求)，则可能引发此异常。

Syntax:

句法：

    public void checkListen(int port_no);

Parameter(s):

参数：

int port_no – represents the local port number.
int port_no –表示本地端口号。

Return value:

返回值：

The return type of this method is void, it returns nothing.

此方法的返回类型为void ，不返回任何内容。

Example:

例：

// Java program to demonstrate the example 
// of void checkListen(int port_no)
// method of SecurityManager 
public class CheckListen extends SecurityManager {
// override checkListen() of SecurityManager
public void checkListen(int port_no) {
throw new SecurityException("No such port exists!!!!");
}
public static void main(String[] args) {
int port_no = 8090;
// By using setProperty() method is to set the policy property 
// with security manager
System.setProperty("java.security.policy", "file:/C:/java.policy");
// Instantiating a CheckListen object
CheckListen cl = new CheckListen();
// By using setSecurityManager() method is to set the
// security manager
System.setSecurityManager(cl);
// By using checkListen(8090) method is to check
// port number 
cl.checkListen(8090);
// Display the message
System.out.println("Not Restricted..");
}
}

Output

输出量

Exception in thread "main" java.lang.SecurityException: No such port exists!!!!at CheckListen.checkListen(CheckListen.java:8)at CheckListen.main(CheckListen.java:27)