java设计模式--Builder模式

一.Builder模式

二.使用例子

三.Spring中的Builder模式

 

Builder模式，构建者、构造者模式，在《图解设计模式》中归为 生成实例 一栏，该模式用于组装具有复杂结构的实例；

　　　　当需要逐步获取对象的初始值时，可以使用Builder模式；

 

一.Builder模式角色

Builder：建造者，Builder角色负责定义用来生成实例的接口API，Builder角色中准备了用于生成实例的具体方法；

ConcreteBuilder：具体的建造者，负责实现Builder接口的的类，定义了生成实例时实际调用的方法，定义了获取最终生成结果的方法；

Director：监工，负责使用Builder角色的接口来生成实例，不依赖于ConcreteBuilder；

 

二.使用例子

Demo：比如有一段预约信息，将其解析为  预约 对象； 预约信息如下："Date, November 5, Headcount, 250, City, Shanghai, DollarsPerHead, 60,HasSite, false"；

date为预约日期，headCount为预期来人数，city为城市，DollarsPerHead为人均预算，hasSite为是否提供地址(比如预约某场演出，是否给表演者提供地点了)；

类结构图：

                                           

预约信息  Reservation.java

@Getter @Setter @ToString //lombok的注解，方便代码查看以及编写 public class Reservation { //Date, November 5, Headcount, 250, City, Shanghai, DollarsPerHead, 60,HasSite, false
    private Date date; private int headCount; private String city; private double dollarsPerHead; private boolean hasSite; }

 

ReservationBuilder.java

public interface ReservationBuilder { public ReservationBuilder futurize(Date date) ; public ReservationBuilder setCity(String city); public ReservationBuilder setDollarsPerHead(double dollarsPerHead); public ReservationBuilder setSite(boolean hasSite); public ReservationBuilder setHeadCount(int headCount); Reservation build(); }

 

 

DefaultReservationBuilder.java

public class DefaultReservationBuilder implements ReservationBuilder{ private Date date; private int headCount; private String city; private double dollarsPerHead; private boolean hasSite; public ReservationBuilder futurize(Date date) { this.date=date; return this; } public ReservationBuilder setCity(String city) { this.city=city; return this; } public ReservationBuilder setDollarsPerHead(double dollarsPerHead) { this.dollarsPerHead=dollarsPerHead; return this; } public ReservationBuilder setSite(boolean hasSite) { this.hasSite=hasSite; return this; } public ReservationBuilder setHeadCount(int headCount) { this.headCount=headCount; return this; } public Reservation build() { Reservation reservation = new Reservation(); reservation.setCity(this.city); reservation.setDate(this.date); reservation.setDollarsPerHead(this.dollarsPerHead); reservation.setHasSite(this.hasSite); reservation.setHeadCount(this.headCount); return reservation; } }

 

 

ReservationDirector.java

public class ReservationDirector { private ReservationBuilder builder; public ReservationDirector(ReservationBuilder builder) { this.builder=builder; } public Reservation construct(String input) throws Exception { String[] strings = input.split(",\\s*"); for(int i=0;i<strings.length-1;i++) { String type=strings[i]; String val=strings[i+1]; if("date".equalsIgnoreCase(type)) { int year = Calendar.getInstance().get(Calendar.YEAR); String res=year+ " "+val.substring(0, 3)+" "+val.substring(val.length()-2); SimpleDateFormat sdf = new SimpleDateFormat("yyyy MMM dd", Locale.ENGLISH); Date date = sdf.parse(res); builder.futurize(date); }else if("headcount".equalsIgnoreCase(type)) { builder.setHeadCount(Integer.valueOf(val)); }else if("city".equalsIgnoreCase(type)) { builder.setCity(val); }else if("dollarsperHead".equalsIgnoreCase(type)) { builder.setDollarsPerHead(Double.parseDouble(val)); }else if("hassite".equalsIgnoreCase(type)) { builder.setSite(Boolean.parseBoolean(val)); } } Reservation reservation = builder.build(); return reservation; } }

 

 

测试方法：

    public static void main(String[] args) throws Exception { //Date, November 5, Headcount, 250, City, Shanghai, DollarsPerHead, 60,HasSite, false
        String input="Date, November 5, Headcount, 20, City, Shanghai, DollarsPerHead, 60,HasSite, false"; ReservationBuilder builder=new DefaultReservationBuilder(); ReservationDirector director=new ReservationDirector(builder); Reservation reservation = director.construct(input); System.out.println(reservation); }

 

 

测试输出：

 

三.Spring中的Builder模式

　　Spring中 RequestMappingInfo中内部接口Builder 、内部静态类DefaultBuilder等，就是采用了Builer模式，RequestMappingInfo就是监工Director对象；类结构图：

              

 

    public interface Builder { /* Set the path patterns*/ Builder paths(String... paths); /* Set the request method conditions*/ Builder methods(RequestMethod... methods);
/* Set the request param conditions*/ Builder params(String... params); /*Set the header conditions*/ Builder headers(String... headers); /* Set the consumes conditions*/ Builder consumes(String... consumes); /* Set the produces conditions*/ Builder produces(String... produces); /* Set the mapping name*/ Builder mappingName(String name); /* Set a custom condition to use*/ Builder customCondition(RequestCondition<?> condition); /* Provide additional configuration needed for request mapping purposes*/ Builder options(BuilderConfiguration options); /** Build the RequestMappingInfo*/ RequestMappingInfo build(); }

 

创建RequestMappingInfo对象地方：作用就是解析RequestMapping注解生成对应RequestMappingInfo对象；    

Builder方法大部分返回值为Builder类型，作用是为了链式执行，看起来生成RequestMappingInfo对象代码只有一句简洁；