java設計模式--Builder模式
摘要：
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，Bu...
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；
