【图解设计模式】Facade模式

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可以为系统提供一个简单窗口。

示例

编写简单的Web页面。

类图

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Database类

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package pagemaker;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;

public class Database {
    private Database() {}

    public static Properties getProperties(String dbname) {
        String filename = dbname + ".txt";
        Properties prop = new Properties();

        try {
            prop.load(new FileInputStream(filename));
        } catch (IOException e) {
            System.out.println("Warning: " + filename + " is not found.");
        }

        return prop;
    }
}

HtmlWriter类

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package pagemaker;

import java.io.IOException;
import java.io.Writer;

public class HtmlWriter {
    private Writer writer;

    public HtmlWriter(Writer writer) {
        this.writer = writer;
    }

    public void title(String title) throws IOException {
        writer.write("<html>");
        writer.write("<head>");
        writer.write("<title>" + title + "</title>");
        writer.write("</head>");
        writer.write("<body>\n");
        writer.write("<h1>" + title + "</h1>\n");
    }

    public void paragraph(String msg) throws IOException {
        writer.write("<p>" + msg + "</p>\n");
    }

    public void link(String href, String caption) throws IOException {
        paragraph("<a href=\"" + href + "\">" + caption + "</a>");
    }

    public void mailto(String mailaddr, String username) throws IOException {
        link("mailto:" + mailaddr, username);
    }

    public void close() throws IOException {
        writer.write("</body>");
        writer.write("</html>\n");
        writer.close();
    }
}

PageMaker类

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package pagemaker;

import java.io.FileWriter;
import java.io.IOException;
import java.util.Properties;

public class PageMaker {
    private PageMaker() {}

    public static void makeWelcomePage(String mailaddr, String filename) {
        try {
            Properties mailprop = Database.getProperties("./xxx/maildata");
            String username = mailprop.getProperty(mailaddr);
            HtmlWriter writer = new HtmlWriter(new FileWriter(filename));
            writer.title("Welcome to " + username + "'s page!");
            writer.paragraph(username + "欢迎来到" + username + "的主页。");
            writer.paragraph("等着你的邮件哦！");
            writer.mailto(mailaddr, username);
            writer.close();
            System.out.println(filename + " is created for " + mailaddr + " (" + username + ")");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Main类

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import pagemaker.PageMaker;

public class Main {

    public static void main(String[] args) {
        PageMaker.makeWelcomePage("hyuki@hyuki.com", "welcome.html");
    }
}

运行结果

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welcome.html is created for hyuki@hyuki.com (Hiroshi Yuki)

m048fI.png

登场角色

Facade（窗口）

Facade角色是代表构成系统的许多其他角色的“简单窗口”。Facade角色向系统外部提供高层接口（API）。在示例程序中，由PageMaker类扮演此角色。

构成系统的许多其他角色

这些角色各自完成自己的工作，它们并不知道Facade角色。Facade角色调用其他角色进行工作，但是其他角色不会调用Facade角色。在示例程序中，由Database类和HtmlWriter类扮演此角色。

Client（请求者）

Client角色负责调用Facade角色。在示例程序中，由Main类扮演此角色。

类图

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