java设计模式--Builder模式
2024-08-24 03:08:57
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;
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