8.1.2 Permissions Explained

Permissions in Java SE 11 are a crucial aspect of security management, allowing developers to control access to system resources and operations. Understanding permissions is essential for building secure and robust applications.

Key Concepts

1. Permission Classes

Permission classes in Java are used to define the type of access that is granted to a particular resource or operation. These classes extend the java.security.Permission class and implement methods such as implies, equals, and hashCode.

Example

        public class MyPermission extends Permission {
            public MyPermission(String name) {
                super(name);
            }
            
            @Override
            public boolean implies(Permission permission) {
                // Implementation
            }
            
            @Override
            public boolean equals(Object obj) {
                // Implementation
            }
            
            @Override
            public int hashCode() {
                // Implementation
            }
            
            @Override
            public String getActions() {
                return "";
            }
        }
    

2. Policy Files

Policy files are configuration files that specify the permissions granted to code from different sources. These files are used by the Java security manager to enforce security policies at runtime.

Example

        grant codeBase "file:/path/to/myapp.jar" {
            permission com.example.MyPermission "exampleAction";
        };
    

3. Security Manager

The Security Manager is a class that enforces security policies in a Java application. It checks for permissions before allowing access to restricted resources or operations.

Example

        System.setSecurityManager(new SecurityManager());
    

4. Access Control Context

The Access Control Context is a representation of the security context in which code is executed. It includes the permissions granted to the code and is used by the security manager to make access control decisions.

Example

        AccessControlContext acc = AccessController.getContext();
    

5. AccessController

The AccessController class is used to perform access control operations, such as checking permissions and executing privileged actions.

Example

        AccessController.checkPermission(new MyPermission("exampleAction"));
    

Examples and Analogies

Think of permissions as keys to a locked room. Each key (permission) grants access to a specific room (resource or operation). The security manager is like a guard who checks the keys before allowing access. Policy files are like a list of keys that the guard uses to verify access. The Access Control Context is like a keyring that holds all the keys the code has access to.

By understanding permissions, you can effectively control access to sensitive resources and operations in your Java SE 11 applications, ensuring they are secure and robust.