Builder模式

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package com.dp.example.builder;

/**
 * Computer产品抽象类, 为了例子简单, 只列出这几个属性
 * 
 * @author mrsimple
 *
 */
public abstract class Computer {

    protected int mCpuCore = 1;
    protected int mRamSize = 0;
    protected String mOs = "Dos";

    protected Computer() {

    }

    // 设置CPU核心数
    public abstract void setCPU(int core);

    // 设置内存
    public abstract void setRAM(int gb);

    // 设置操作系统
    public abstract void setOs(String os);

    @Override
    public String toString() {
        return "Computer [mCpuCore=" + mCpuCore + ", mRamSize=" + mRamSize
                + ", mOs=" + mOs + "]";
    }

}

package com.dp.example.builder;

/**
 * Apple电脑
 */
public class AppleComputer extends Computer {

    protected AppleComputer() {

    }

    @Override
    public void setCPU(int core) {
        mCpuCore = core;
    }

    @Override
    public void setRAM(int gb) {
        mRamSize = gb;
    }

    @Override
    public void setOs(String os) {
        mOs = os;
    }

}

package com.dp.example.builder;


package com.dp.example.builder;

/**
 * builder抽象类
 *
 */
public abstract class Builder {
    // 设置CPU核心数
    public abstract void buildCPU(int core);

    // 设置内存
    public abstract void buildRAM(int gb);

    // 设置操作系统
    public abstract void buildOs(String os);

    // 创建Computer
    public abstract Computer create();

}

package com.dp.example.builder;

public class ApplePCBuilder extends Builder {
    private Computer mApplePc = new AppleComputer();

    @Override
    public void buildCPU(int core) {
        mApplePc.setCPU(core);
    }

    @Override
    public void buildRAM(int gb) {
        mApplePc.setRAM(gb);
    }

    @Override
    public void buildOs(String os) {
        mApplePc.setOs(os);
    }

    @Override
    public Computer create() {
        return mApplePc;
    }

}

package com.dp.example.builder;

public class Director {
    Builder mBuilder = null;

    /**
     * 
     * @param builder
     */
    public Director(Builder builder) {
        mBuilder = builder;
    }

    /**
     * 构建对象
     * 
     * @param cpu
     * @param ram
     * @param os
     */
    public void construct(int cpu, int ram, String os) {
        mBuilder.buildCPU(cpu);
        mBuilder.buildRAM(ram);
        mBuilder.buildOs(os);
    }
}

/**
 * 经典实现较为繁琐
 * 
 * @author mrsimple
 *
 */
public class Test {
    public static void main(String[] args) {
        // 构建器
        Builder builder = new ApplePCBuilder();
        // Director
        Director pcDirector = new Director(builder);
        // 封装构建过程, 4核, 内存2GB, Mac系统
        pcDirector.construct(4, 2, "Mac OS X 10.9.1");
        // 构建电脑, 输出相关信息
        System.out.println("Computer Info : " + builder.create().toString());
    }
}

通过Builder来构建产品对象, 而Director封装了构建复杂产品对象对象的过程, 不对外隐藏构建细节. 实践中Director角色经常会被省略, 直接使用Builder进行对象组装. 在开发中一般用于这样的场景: 把一些配置参数单独放在一个类中(Config类), 把构建过程放在这个类的静态内部类中(Builder类), 通过Builder的链式调用产生Config类对象, 再注入到产品类中.