java設計模式--Builder模式
三.Spring中的Builder模式
Builder模式,構建者、構造者模式,在《圖解設計模式》中歸為 生成例項 一欄,該模式用於組裝具有複雜結構的例項;
當需要逐步獲取物件的初始值時,可以使用Builder模式;
一.Builder模式角色
Builder:建造者,Builder角色負責定義用來生成例項的介面API,Builder角色中準備了用於生成例項的具體方法;
ConcreteBuilder:具體的建造者,負責實現Builder介面的的類,定義了生成例項時實際呼叫的方法,定義了獲取最終生成結果的方法;
Director:監工,負責使用Builder角色的介面來生成例項,不依賴於ConcreteBuilder;
二.使用例子
Demo:比如有一段預約資訊,將其解析為 預約 物件; 預約資訊如下:"Date, November 5, Headcount, 250, City, Shanghai, DollarsPerHead, 60,HasSite, false";
date為預約日期,headCount為預期來人數,city為城市,DollarsPerHead為人均預算,hasSite為是否提供地址(比如預約某場演出,是否給表演者提供地點了);
類結構圖:
預約資訊 Reservation.java
@Getter @Setter @ToString//lombok的註解,方便程式碼檢視以及編寫 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; } }
測試方法:
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); }
測試輸出:
三.Spring中的Builder模式
Spring中 RequestMappingInfo中內部介面Builder 、內部靜態類DefaultBuilder等,就是採用了Builer模式,RequestMappingInfo就是監工Director物件;類結構圖:
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(); }
建立RequestMappingInfo物件地方:作用就是解析RequestMapping註解生成對應RequestMappingInfo物件;
Builder方法大部分返回值為Builder型別,作用是為了鏈式執行,看起來生成RequestMappingInfo物件程式碼只有一句簡潔;