一、什么是Builder模式？
builder模式，就好比一栋大楼，这栋大楼有很多个组件组成，但是这栋大楼只是一个各个组件结合起来的框架，每一栋大楼都有各自的特色，这些特色由它们实际情况决定。对于程序而言，这栋大楼就好比一个Builder抽象类，里面定义了很多组件方法，一个完整的功能离不开里面的每一个方法，具体实现依赖子类，只要继承这个抽象类，就可以根据组件方法组建起自己的“大楼”。
二、Builder模式思想
Builder类：负责生成实例的接口，里面定义了用于生成实例的方法；
ConcreteBuilder类：负责实现Builder抽象类，此外还定义了获取最终结果（大楼）的方法；
Director类：负责使用Builder抽象类生成实例，它并不依赖Builder的具体子类，所以它只会调用Builder里面定义的方法。
三、应用实例
设计一个Builder，用于编写文档，可以是Text文档，也可以是HTML文档。
1、Builder类
package com.cjs.builder;
public abstract class Builder {
public abstract void makeTitle(String title);
public abstract void makeString(String str);
public abstract void makeItem(String[] items);
public abstract void close();
}
2、Director类
package com.cjs.builder;
public class Director {
Builder builder;
public Director(Builder builder) {
this.builder = builder;
}
public void construct() {
builder.makeTitle("Greeting");
builder.makeString("从早上至下午");
builder.makeItem(new String[]{"Good Morning", "Good Afternoon"});
builder.makeString("晚上");
builder.makeItem(new String[]{"Good Night","Bye-Bye"});
builder.close();
}
}
3、TextBuilder类
package com.cjs.builder;
public class TextBuilder extends Builder {
private StringBuilder buffer = new StringBuilder();
@Override
public void makeTitle(String title) {
buffer.append("=========================
");
buffer.append("[" + title + "]
");
buffer.append("
");
}
@Override
public void makeString(String str) {
buffer.append("■" + str + "
");
buffer.append("
");
}
@Override
public void makeItem(String[] items) {
for (int i = 0; i < items.length; i++) {
buffer.append(" ·" + items[i] + "
");
buffer.append("
");
}
}
@Override
public void close() {
buffer.append("=========================
");
}
public String getResult() {
return buffer.toString();
}
}
4、HTMLBuilder类
package com.cjs.builder;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
public class HTMLBuilder extends Builder {
private String fileName;
private PrintWriter writer;
@Override
public void makeTitle(String title) {
fileName = title + ".html";
try {
writer = new PrintWriter(new FileWriter(fileName));
} catch (IOException e) {
e.printStackTrace();
}
writer.println("<html><head><title>" + title + "</title></head><body>");
writer.println("<h1>"+title+"</h1>");
}
@Override
public void makeString(String str) {
writer.println("<p>"+str+"</p>");
}
@Override
public void makeItem(String[] items) {
writer.println("<ul>");
for (int i = 0; i < items.length; i++) {
writer.println("<li>" + items[i] + "</li>");
}
writer.println("</ul>");
}
@Override
public void close() {
writer.println("</body></head");
writer.close();
}
public String getResult() {
return fileName;
}
}
5、Main类
package com.cjs.builder;
public class Main {
public static void main(String[] args) {
if (args.length != 1) {
usage();
System.exit(0);
}
if (args[0].equals("plain")) {
TextBuilder textBuilder = new TextBuilder();
Director director = new Director(textBuilder);
director.construct();
String result = textBuilder.getResult();
System.out.println(result);
} else if (args[0].equals("html")) {
HTMLBuilder htmlBuilder = new HTMLBuilder();
Director director = new Director(htmlBuilder);
director.construct();
System.out.println(htmlBuilder.getResult()+"文件编写完成");
} else {
usage();
System.exit(0);
}
}
public static void usage() {
System.out.println("Usage: java main plain 编写文本文档");
System.out.println("Usage: java main html 编写HTML文档");
}
}
对于Director类，它并不关心实际编写文档是采用纯文本，还是HTML，所以在Builder抽象类里必须声明足够多的方法，同时，Builder类的实现类可以拥有自己独特的方法，以实现各自对实际情况的逻辑需求。