代理模式【PROXY PATTERN】-优快云博客

本文链接：https://blog.youkuaiyun.com/chenhongwei0924/article/details/83797396

本文通过一个简单的Java程序演示了代理模式的应用。程序定义了一个打印接口和实现该接口的真实打印类及代理类。代理类在调用真实打印类之前可以进行额外的操作。

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public class Main
{
    public static void main(String[] args)
    {
        PrinterProxy p = new PrinterProxy("Alice");
        System.out.println(p.getPrinterName());
        p.setPrinterName("Bob");
        System.out.println(p.getPrinterName());
        p.print("Hello, world.");
    }
}

interface Printable
{
    public abstract void setPrinterName(String name);

    public abstract String getPrinterName();

    public abstract void print(String string);
}

class Printer implements Printable
{
    private String name;

    public Printer()
    {
        heavyJob("Printer");
    }

    public Printer(String name)
    {
        this.name = name;
        heavyJob("Printer（）" + name);
    }

    public void setPrinterName(String name)
    {
        this.name = name;
    }

    public String getPrinterName()
    {
        return name;
    }

    public void print(String string)
    {
        System.out.println("=== " + name + " ===");
        System.out.println(string);
    }

    private void heavyJob(String msg)
    {
        System.out.println(msg);
        for (int i = 0; i < 5; i++)
        {
            try
            {
                Thread.sleep(1000);
            }
            catch (InterruptedException e)
            {
            }
            System.out.print(".");
        }
    }
}

class PrinterProxy implements Printable
{
    private String name;

    private Printer real;

    public PrinterProxy()
    {
    }

    public PrinterProxy(String name)
    {
        this.name = name;
    }

    public synchronized void setPrinterName(String name)
    {
        if (real != null)
        {
            real.setPrinterName(name);
        }
        this.name = name;
    }

    public String getPrinterName()
    {
        return name;
    }

    public void print(String string)
    {
        realize();
        real.print(string);
    }

    private synchronized void realize()
    {
        if (real == null)
        {
            real = new Printer(name);
        }
    }
}