Java SecurityManager checkPermission（）方法与示例

Syntax:

句法：

    public void checkPermission(Permission  perm);
public void checkPermission(Permission  perm, Object cntxt);

SecurityManager类的checkPermission()方法 (SecurityManager Class checkPermission() method)

checkPermission() method is available in java.lang package.
checkPermission()方法在java.lang包中可用。
checkPermission(Permission perm) method invokes checkPermission of AccesController for the requested access, indicated by the specified permissions.
checkPermission(Permission perm)方法为请求的访问调用AccesController的checkPermission，由指定的权限指示。
checkPermission(Permission perm, Object cntxt) method invokes checkPermission of AccesControlContext for the given security context is the access granted to the resource, indicated by the specified permissions when cntxt is an instance of AccessControlContext.
当给定的安全上下文是授予资源的访问权限时，checkPermission(Permission perm，Object cntxt)方法调用AccesControlContext的checkPermission，当cntxt是AccessControlContext的实例时，由指定的权限表示。
checkPermission(Permission perm), checkPermission(Permission perm, Object cntxt) methods may throw an exception at the time of granting permission.
checkPermission(Permission perm)和checkPermission(Permission perm，Object cntxt)方法在授予权限时可能会引发异常。
checkPermission(Permission perm):
checkPermission(权限烫发)：
- SecurityException – This exception may throw when the access is denied on the security policy held currently.
- NullPointerException – This exception may throw when the given parameter is null.
checkPermission(Permission perm, Object cntxt):
checkPermission(权限权限，对象cntxt)：
- SecurityException – This exception may throw when the calling thread is not allowed to access the resource by the given permission or when the security cntxt(context) is not an object of AccessControlContext.
- NullPointerException – This exception may throw when the given first parameter is null.
These are non-static methods, it is accessible with the class object only and, if we try to access these methods with the class name then we will get an error.
这些是非静态方法，只能通过类对象访问，如果尝试使用类名称访问这些方法，则会收到错误消息。

Parameter(s):

参数：

In the first case, Permission perm - This parameter represents the requested permission.
在第一种情况下，权限权限 -此参数表示请求的权限。
In the second case, Permission perm, Object cntxt
在第二种情况下，权限权限，对象cntxt
- Permission perm – Similar as defined in the first case.
- 许可权限 –与第一种情况中定义的相似。
- Object cntxt – This parameter represents the system-specific security context.
- 对象cntxt –此参数表示系统特定的安全上下文。

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 checkPermission() method of SecurityManager class
import java.security.*;
import java.io.*;
public class CheckPermission extends SecurityManager {
public static void main(String[] args) {
Permission perm = new FilePermission("getProperties().doc", "read,write");
AccessControlContext acc = AccessController.getContext();
// By using setProperty() method is to set the policy property 
// with security manager
System.setProperty("java.security.policy", "file:/C:/java.policy");
// Instantiating a CheckPermission object
CheckPermission cp = new CheckPermission();
// By using setSecurityManager() method is to set the
// security manager
System.setSecurityManager(cp);
// By using checkPermission(Permission) method is to
// check that restricted permission
cp.checkPermission(perm);
// By using checkPermission(Permission,Object) method is to
// check that restricted permission when cntxt is an instance
// of AccessControlContext
cp.checkPermission(perm, acc);
// Display the message 
System.out.println("Accepted..");
}
}

Output

输出量

Exception in thread "main" java.security.AccessControlException: access denied ("java.io.FilePermission" "getProperties().doc" "read,write")at java.base/java.security.AccessControlContext.checkPermission(AccessControlContext.java:472)at java.base/java.security.AccessController.checkPermission(AccessController.java:897)at java.base/java.lang.SecurityManager.checkPermission(SecurityManager.java:322)at CheckPermission.main(CheckPermission.java:25)