建造者(Builder)模式

如果说工厂模式是在创建对象的话，那么Builder模式就是一个“精工细作”的过程。
Builder模式用于把产品创建的每个步骤封装起来，对客户端关闭。

首先，我们制作一个抽象的产品，假设有2个部件：

package dp.builder.general;

public interface Product {
	void setPart1(String part1);
	void setPart2(String part2);
}

然后是实际的产品：

public class Product1 implements Product {
	
	private String part1;
	private String part2;
	
	public Product1() {
		part1 = "";
		part2 = "";
	}
	
	public void setPart1(String part1) {
		this.part1 = part1;
	}
	
	public void setPart2(String part2) {
		this.part2 = part2;
	}
	
	public String toString() {
		return "Product1: " + part1 + ", " + part2;
	}
}

package dp.builder.general;

public class Product2 implements Product {
	
	private String part1;
	private String part2;
	
	public Product2() {
		part1 = "";
		part2 = "";
	}
	
	public void setPart1(String part1) {
		this.part1 = part1;
	}
	
	public void setPart2(String part2) {
		this.part2 = part2;
	}
	
	public String toString() {
		return "Product2: " + part1 + ", " + part2;
	}
}

接着，我们创建Builder接口，它负责装配产品部件，显示产品结果：

package dp.builder.general;

abstract public class Builder {
	
	public abstract void buildPart1();

	public abstract void buildPart2();

	public abstract String retrieveResult();
}

实际的建造者：

package dp.builder.general;

public class ConcreteBuilder1 extends Builder {
	
	private Product1 product = new Product1();

	public void buildPart1() {
		product.setPart1("ConcreteBuilder1->part1");
	}

	public void buildPart2() {
		product.setPart2("ConcreteBuilder1->part2");
	}

	public String retrieveResult() {
		return product.toString();
	}
}

package dp.builder.general;

public class ConcreteBuilder2 extends Builder {
	
	private Product2 product = new Product2();

	public void buildPart1() {
		product.setPart1("ConcreteBuilder2->part1");
	}

	public void buildPart2() {
		product.setPart2("ConcreteBuilder2->part2");
	}

	public String retrieveResult() {
		return product.toString();
	}
}

然后，我们设置一个导演，它用来组织实际的建造者：

package dp.builder.general;

public class Director {

	private Builder builder;

	public Director(Builder builder) {
		this.builder = builder;
	}

	public void construct() {
		builder.buildPart1();

		builder.buildPart2();

		System.out.println(builder.retrieveResult());
	}
}

最后，客户端和导演以及建造者打交道，对于实际产品关闭：

package dp.builder.general;

public class Client {

	public static void main(String[] args) {
		Director director = null;
		
		System.out.println("****** Built By Concrete Builder 1 ******");
		Builder builder1 = new ConcreteBuilder1();
		director = new Director(builder1);
		director.construct();
		
		System.out.println("****** Built By Concrete Builder 2 ******");
		Builder builder2 = new ConcreteBuilder2();
		director = new Director(builder2);
		director.construct();

	}

}

运行结果：
****** Built By Concrete Builder 1 ******
Product1: ConcreteBuilder1->part1, ConcreteBuilder1->part2
****** Built By Concrete Builder 2 ******
Product2: ConcreteBuilder2->part1, ConcreteBuilder2->part2