场景

• 我们要建造一个复杂的产品。比如：神州飞船，iPhone。这个复杂的产品的创建。有这样一个问题需要处理：装配这些子组件是不是有个步骤问题？
• 实际开发中，我们所需要的对象构建时，也非常复杂，有很多步骤需要处理时。

建造者模式的本质

• 分离了对象子组件的单独构造(由Builder来负责)和装配(由Director负责)。从而可以构造出复杂的对象。这个模式适用于：某个对象的构建过程复杂的情况下使用。
• 由于实现了构建和装配的解耦。不同的构建器，相同的装配，也可以做出不同的对象；相同的构建器，不同的装备顺序也可以做出不同的对象。也就是实现了构建算法、装配算法的解耦，实现了更好的复用。

示例

package builder;

public class AirShip {
    private OrbitalModule orbitalModule;    // 轨道舱
    private Engine engine;                          // 发动机
    private EscapeTower escapeTower;     // 逃逸塔

    public void launch(){
        System.out.println("发射");
    }

    public OrbitalModule getOrbitalModule() {
        return orbitalModule;
    }

    public void setOrbitalModule(OrbitalModule orbitalModule) {
        this.orbitalModule = orbitalModule;
    }

    public Engine getEngine() {
        return engine;
    }

    public void setEngine(Engine engine) {
        this.engine = engine;
    }

    public EscapeTower getEscapeTower() {
        return escapeTower;
    }

    public void setEscapeTower(EscapeTower escapeTower) {
        this.escapeTower = escapeTower;
    }
}

class OrbitalModule{
    private String name;

    public OrbitalModule(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

class Engine{
    private String name;

    public Engine(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

class EscapeTower{
    private String name;

    public EscapeTower(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

package builder;

public interface AirShipBuilder {
    Engine builderEngine();
    OrbitalModule builderOrbitalModule();
    EscapeTower builderEscapeTower();
}

package builder;

public interface AirShipDirector {
    /**
     * 组装飞船对象
     * @return
     */
    AirShip directAirShip();
}

package builder;

public class MyAirShipBuilder implements AirShipBuilder{
    //StringBuilder,DomBuilder,SaxBuilder
    public Engine builderEngine() {
        System.out.println("构建发动机");
        return new Engine("发动机");
    }

    public OrbitalModule builderOrbitalModule() {
        System.out.println("构建轨道舱");
        return new OrbitalModule("轨道舱");
    }

    public EscapeTower builderEscapeTower() {
        System.out.println("构建逃逸塔");
        return new EscapeTower("逃逸塔");
    }
}

package builder;

public class MyAirShipDirector implements AirShipDirector{
    private AirShipBuilder builder;

    public MyAirShipDirector(AirShipBuilder builder) {
        this.builder = builder;
    }

    public AirShip directAirShip() {
        Engine engine = builder.builderEngine();
        OrbitalModule orbitalModule = builder.builderOrbitalModule();
        EscapeTower escapeTower = builder.builderEscapeTower();
        //装配
        AirShip airShip = new AirShip();
        airShip.setEngine(engine);
        airShip.setOrbitalModule(orbitalModule);
        airShip.setEscapeTower(escapeTower);
        return airShip;
    }
}

package builder;

public class Client {
    public static void main(String[] args) {
        AirShipDirector director = new MyAirShipDirector(new MyAirShipBuilder());
        AirShip airShip = director.directAirShip();
        System.out.println(airShip.getEngine().getName());
        airShip.launch();
    }
}

开发中应用场景:

• StringBuilder类的append方法
• SQL中的PreparedStatement
• JDOM中,DomBuilder、SAXBuilder