设计模式生成器模式

概述

　　将复杂对象的构建与表示分离，使得同样的构建过程可以创建不同的表示。

适用场景

　　1）构建一个复杂对象，该复杂对象内部往往有许多部件（域）待初始化；

　　2）通过不同的生成器，就可生成相应的复杂对象；

结构

　　

　　1）Product：即产品类。该类很复杂，它包含的域待初始化；

　　2）Builder：抽象Builder类。它需要指定Product对象中各部件的生成方法：buildPart()；

　　3）ConcreteBuilder：Builder类的一个实现。它包含一个待初始化的Product对象，通过对其组件进行初始化，并提供一个成型对象的方法；

　　4）Director：建造者。它包含一个抽象Builder对象，通过不同的Builder实现类，可生成不同的Product对象；在此过程中，也可选择性初始化部分组件，很灵活。

实例：

　　Product有2个组件：component1和component2; Builder有2个实现类，生成含有不同组件组合的Product。

Product:

package org.wgx.pattern.builder;

public class Product {
    private String name = "";
    private String component1 = "";
    private String component2 = "";
    
    public Product(String name) {
        this.name = name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public void setComponent1(String c1) {
        this.component1 = c1;
    }
    
    public void setComponent2(String c2) {
        this.component2 = c2;
    }
    
    public String toString() {
        String result = "This is Product: " + name + ", component1 is " + component1 + ", component2 is " + component2 + "\r\n";
        return result;
    }
}

Builder：

package org.wgx.pattern.builder;

public interface Builder {
    public void buildComponent1();
    public void buildComponent2();
    public Product getProduct();
}

ConcreteBuilderOne：

package org.wgx.pattern.builder;

public class ConcreteBuilderOne implements Builder {
    
    private Product product;
    
    public ConcreteBuilderOne() {
        product = new Product("first product");
    }
    
    @Override
    public void buildComponent1() {
        // TODO Auto-generated method stub
        this.product.setComponent1("1a");
    }

    @Override
    public void buildComponent2() {
        // TODO Auto-generated method stub
        this.product.setComponent2("2a");
    }

    @Override
    public Product getProduct() {
        // TODO Auto-generated method stub
        return this.product;
    }

}

ConcreteBuilderTwo：

package org.wgx.pattern.builder;

public class ConcreteBuilderTwo implements Builder {

    private Product product;
    
    public ConcreteBuilderTwo() {
        product = new Product("second product");
    }
        
    @Override
    public void buildComponent1() {
        // TODO Auto-generated method stub
        this.product.setComponent1("1b");
    }

    @Override
    public void buildComponent2() {
        // TODO Auto-generated method stub
        this.product.setComponent2("2b");
    }

    @Override
    public Product getProduct() {
        // TODO Auto-generated method stub
        return this.product;
    }

}

Director：

package org.wgx.pattern.builder;

public class Director {
    private Builder builder;
    
    public Director(Builder builder) {
        this.builder = builder;
    }
    
    public Product constructProduct() {
        builder.buildComponent1();
        builder.buildComponent2();
        return builder.getProduct();
    }
    
}

Client：

package org.wgx.pattern.builder;

public class Client {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Builder builder1 = new ConcreteBuilderOne();
        Director director1 = new Director(builder1);
        System.out.println(director1.constructProduct());
            
        Builder builder2 = new ConcreteBuilderTwo();
        Director director2 = new Director(builder2);
        System.out.println(director2.constructProduct());
    }

}

结果：

This is Product: first product, component1 is 1a, component2 is 2a

This is Product: second product, component1 is 1b, component2 is 2b