外观模式(Facade Pattern)可以为互相关联在一起的错综复杂的类整理出高层接口。
Database.java
package com.test.dp.Facade.Sample.pagemaker;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;
//从邮件地址中获取用户名的类
public class Database {
private Database() { // 防止外部new出Database的实例,所以声明为private方法
}
public static Properties getProperties(String dbname) { // 根据数据库名获取Properties
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;
}
}
maildata.txt
[email protected]=Hiroshi Yuki
[email protected]=Hanako Sato
[email protected]=Tomura
[email protected]=Mamoru Takahashi
HtmlWriter.java
package com.test.dp.Facade.Sample.pagemaker;
import java.io.Writer;
import java.io.IOException;
//编写HTML文件的类
public class HtmlWriter {
private Writer writer;
public HtmlWriter(Writer writer) { // 构造函数
this.writer = writer;
}
public void title(String title) throws IOException { // 输出标题
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 { // 输出段落
writer.write("<p>" + msg + "</p>\n");
}
public void link(String href, String caption) throws IOException { // 输出超链接
paragraph("<a href=\"" + href + "\">" + caption + "</a>");
}
public void mailto(String mailaddr, String username) throws IOException { // 输出邮件地址
link("mailto:" + mailaddr, username);
}
public void close() throws IOException { // 结束输出HTML
writer.write("</body>");
writer.write("</html>\n");
writer.close();
}
}
PageMaker.java
package com.test.dp.Facade.Sample.pagemaker;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Properties;
//根据邮件地址编写用户的Web页面
public class PageMaker {
private PageMaker() { // 防止外部new出PageMaker的实例,所以声明为private方法
}
public static void makeWelcomePage(String mailaddr, String filename) {
try {
Properties mailprop = Database.getProperties("maildata");
String username = mailprop.getProperty(mailaddr);
HtmlWriter writer = new HtmlWriter(new FileWriter(filename));
writer.title("Welcome to " + username + "'s page!");
writer.paragraph("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.java
package com.test.dp.Facade.Sample;
import com.test.dp.Facade.Sample.pagemaker.PageMaker;
public class Main {
public static void main(String[] args) {
PageMaker.makeWelcomePage("[email protected]", "welcome.html");
}
}
执行结果:
略
总结:
应用实例:1、去医院看病,可能要去挂号、门诊、划价、取药,让患者或患者家属觉得很复杂,如果有提供接待人员,只让接待人员来处理,就很方便。2、JAVA 的三层开发模式。
优点:1、减少系统相互依赖。2、提高灵活性。3、提高了安全性。
缺点:不符合开闭原则,如果要改东西很麻烦,继承重写都不合适。
使用场景:1、为复杂的模块或子系统提供外界访问的模块。2、子系统相对独立。3、预防低水平人员带来的风险。
注意事项:在层次化结构中,可以使用外观模式定义系统中每一层的入口。