外觀模式(Facade Pattern)可以為互相關聯在一起的錯綜複雜的類整理出高層接口。
Database.java
package com.test.dp.Facade.Sample.pagemaker;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;
//從郵件位址中擷取使用者名的類
public class Database {
private Database() { // 防止外部new出Database的執行個體,是以聲明為private方法
}
public static Properties getProperties(String dbname) { // 根據資料庫名擷取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;
//編寫HTML檔案的類
public class HtmlWriter {
private Writer writer;
public HtmlWriter(Writer writer) { // 構造函數
this.writer = writer;
}
public void title(String title) throws IOException { // 輸出标題
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 { // 輸出段落
writer.write("<p>" + msg + "</p>\n");
}
public void link(String href, String caption) throws IOException { // 輸出超連結
paragraph("<a href=\"" + href + "\">" + caption + "</a>");
}
public void mailto(String mailaddr, String username) throws IOException { // 輸出郵件位址
link("mailto:" + mailaddr, username);
}
public void close() throws IOException { // 結束輸出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;
//根據郵件位址編寫使用者的Web頁面
public class PageMaker {
private PageMaker() { // 防止外部new出PageMaker的執行個體,是以聲明為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("歡迎來到" + username + "的首頁。");
writer.paragraph("等着你的郵件哦!");
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");
}
}
執行結果:
略
總結:
應用執行個體:1、去醫院看病,可能要去挂号、門診、劃價、取藥,讓患者或患者家屬覺得很複雜,如果有提供接待人員,隻讓接待人員來處理,就很友善。2、JAVA 的三層開發模式。
優點:1、減少系統互相依賴。2、提高靈活性。3、提高了安全性。
缺點:不符合開閉原則,如果要改東西很麻煩,繼承重寫都不合适。
使用場景:1、為複雜的子產品或子系統提供外界通路的子產品。2、子系統相對獨立。3、預防低水準人員帶來的風險。
注意事項:在階層化結構中,可以使用外觀模式定義系統中每一層的入口。