Xing's Techlog

建造者模式（Builder Pattern）

Posted on Edited on In

当我们要构造的对象非常复杂，即对象中的组件需要有顺序的被构建时，就应该使用建造者模式。

实际开发中，建造者模式通常用来构造复杂对象。建造者模式分离了对象子组件的构造（Build）和装配（Direct），构造由Builder负责，装配有Director负责。每个组件由Builder单独构建，然后再交给Director组装，从而可以构造出非常复杂的对象。

由于实现了构造和装配的解耦，不同的Builder，相同的Director，也可以造出不同对象。相同的Builder，不同的Director也可以做出不同的对象。也就是实现了构造算法、装配算法的解耦，实现了更好的复用。

建造者模式UML如下图所示：

建造者模式UML

组件类定义：

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public class OrbitalModule{
4private String name;
4public OrbitalModule(String name) {
44this.name = name;
4}
4public String getName() {
44return name;
4}
4public void setName(String name) {
44this.name = name;
4}
}
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public class Engine {
4private String name;
4public Engine(String name) {
44this.name = name;
4}
4public String getName() {
44return name;
4}
4public void setName(String name) {
44this.name = name;
4}
}
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class EscapeTower{
4private String name;
4public String getName() {
44return name;
4}
4public void setName(String name) {
44this.name = name;
4}
4public EscapeTower(String name) {
44super();
44this.name = name;
4}	
}

飞船类定义：

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public class AirShip {
4private OrbitalModule orbitalModule;  //轨道舱
4private Engine engine; //发动机
4private EscapeTower escapeTower;  //逃逸塔
4
    //这里可以自定义方法
    public void lunch(){}
    
4public OrbitalModule getOrbitalModule() {
44return orbitalModule;
4}
4public void setOrbitalModule(OrbitalModule orbitalModule) {
44this.orbitalModule = orbitalModule;
4}
4public Engine getEngine() {
44return engine;
4}
4public void setEngine(Engine engine) {
44this.engine = engine;
4}
4public EscapeTower getEscapeTower() {
44return escapeTower;
4}
4public void setEscapeTower(EscapeTower escapeTower) {
44this.escapeTower = escapeTower;
4}
}

Builder接口：

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public interface AirShipBuilder {
4Engine builderEngine();
4OrbitalModule builderOrbitalModule();
4EscapeTower  builderEscapeTower();
}

Builder实现类：

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public class MyAirShipBuilder implements AirShipBuilder {
4@Override
4public Engine builderEngine() {
44return new Engine("MyEngine");
4}
4@Override
4public EscapeTower builderEscapeTower() {
44return new EscapeTower("MyEscapeTower");
4}
4@Override
4public OrbitalModule builderOrbitalModule() {
44return new OrbitalModule("MyOrbitalModule");
4}	
}

Director接口：

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public interface AirShipDirector {
4AirShip   directAirShip();	
}

Director实现类：

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public class MyAirshipDirector implements AirShipDirector {
4private AirShipBuilder builder;
4public MyAirshipDirector(AirShipBuilder builder) {
44this.builder = builder;
4}
4@Override
4public AirShip directAirShip() {
44Engine e = builder.builderEngine();
44OrbitalModule o = builder.builderOrbitalModule();
44EscapeTower et = builder.builderEscapeTower();
44AirShip ship = new AirShip();
44ship.setEngine(e);
44ship.setEscapeTower(et);
44ship.setOrbitalModule(o);
44return ship;
4}
}

Client:

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public class Client {
4public static void main(String[] args) {
44AirShipDirector director = new SxtAirshipDirector(new SxtAirShipBuilder());
44AirShip ship = director.directAirShip(); //到这里就构建好了一个Airship
44
        ship.launch(); //调用自定义方法
4}
}

典型应用场景：

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