Java设计模式之代理模式详解

// 真实主题类，用于读取文件
public class RealFile {
    private String filename;

    public RealFile(String filename) {
        this.filename = filename;
    }

    public String readFile() {
        String content = readFromFile(filename);
        return content;
    }

    private String readFromFile(String filename) {
        // 实际读取文件并返回内容
        return "";
    }
}

// 文件读取代理类
public class FileProxy implements RealFile {
    private RealFile realFile;
    private int count = 0;

    public FileProxy(RealFile realFile) {
        this.realFile = realFile;
    }

    @Override
    public String readFile() {
        String content = realFile.readFile();
        // 在读取文件之前执行额外功能
        System.out.println("ReadFile called " + ++count + " times");
        // 在读取文件之后执行额外功能
        System.out.println("ReadFile returned " + content);
        return content;
    }
}

RealFile realFile = new RealFile("file.txt");
FileProxy proxy = new FileProxy(realFile);

String content = proxy.readFile();