设计模式-建造者模式

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建造者模式

定义

建造者模式（Builder Pattern）使用多个简单的对象一步一步构建成一个复杂的对象。这种类型的设计模式属于创建型模式，它提供了一种创建对象的最佳方式。

一个 Builder 类会一步一步构造最终的对象。该 Builder 类是独立于其他对象的。

类图

建造者模式类图

Builder（建造者）

负责定义用于生成实例的接口。准备了用于生成实例的方法

ConcreteBuilder（具体的建造者）

负责实现Builder角色的接口的类。定义了在生成实例时实际被调用的方法。此外，还定义了获取最终结果的方法。

Director（监工）

负责使用Builder的接口生成实例，不依赖于ConcreteBuilder。为了确保不论ConcreteBuilder是如何被定义的，Director都能正常工作，它只调用在Builder中被定义的方法。

Client（使用者）

使用了Builder模式

建造者模式时序图

示例

类图

建造者模式示例类图

Builder

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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();
}

Director

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public class Director {
	private Builder builder;
	
	public Director(Builder builder) {
		this.builder = builder;
	}
	
	public void construct() {
		builder.makeTitle("Greating");
		builder.makeString("from morning to afternoon");
		builder.makeItem(new String[] {"Good morning", "Good afternoon"});
		builder.makeString("Evening");
		builder.makeItem(new String[] {"Good evening", "Good night", "Bye"});
		builder.close();
	}
}

HTMLBuilder

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public class HTMLBuilder extends Builder {
	private String fileName;
	
	private PrintWriter writer;

	@Override
	public void makeTitle(String title) {
		// TODO Auto-generated method stub
		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) {
		// TODO Auto-generated method stub
		writer.println("<p>" + str + "</p>");
	}

	@Override
	public void makeItem(String[] items) {
		// TODO Auto-generated method stub
		writer.println("<ul>");
		for (int i = 0;i < items.length;i++) {
			writer.println("<li>" + items[i] + "</li>");
		}
		writer.println("</ul>");
	}

	@Override
	public void close() {
		// TODO Auto-generated method stub
		writer.println("</body></html>");
		writer.close();
	}
	
	public String getResult() {
		return fileName;
	}
	
}

TextBuilder

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public class TextBuilder extends Builder {
	private StringBuffer buffer = new StringBuffer();

	@Override
	public void makeTitle(String title) {
		// TODO Auto-generated method stub
		buffer.append("================================\n");
		buffer.append("[" + title + "]\n");
		buffer.append("\n");
	}

	@Override
	public void makeString(String str) {
		// TODO Auto-generated method stub
		buffer.append(" " + str + "\n");
		buffer.append("\n");
	}

	@Override
	public void makeItem(String[] items) {
		// TODO Auto-generated method stub
		for (int i = 0;i < items.length;i++) {
			buffer.append("  .  " + items[i] + "\n");
		}
		buffer.append("\n");
	}

	@Override
	public void close() {
		// TODO Auto-generated method stub
		buffer.append("================================\n");
	}
	
	public String getResult() {
		return buffer.toString();
	}
}

Main

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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();
			String result = htmlBuilder.getResult();
			System.out.println(result + " 文件编写完成");
		} else {
			usage();
			System.exit(0);
		}
	}
	
	public static void usage() {
		System.out.println("Usage: java main plain    编写纯文本文档");
		System.out.println("Usage: java main html     编写html文档");
	}
}

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