Spring bean三种创建方式

Posted 2020-07-31 JustDo

　　spring共提供了三种实例化bean的方式：构造器实例化  静态工厂实例化   动态工厂实例化，下面一一详解：

 

1、构造器实例化

City.java

 1 package com.proc.bean;
 2 
 3 public class City {
 4 
 5     private String name;
 6     private String code;
 7     
 8     public City() {
 9     }
10 
11     public City(String name, String code) {
12         this.name = name;
13         this.code = code;
14     }
15 
16     public String getName() {
17         return name;
18     }
19 
20     public void setName(String name) {
21         this.name = name;
22     }
23 
24     public String getCode() {
25         return code;
26     }
27 
28     public void setCode(String code) {
29         this.code = code;
30     }
31 
32     @Override
33     public String toString() {
34         return "City [name=" + name + ", code=" + code + "]";
35     }
36 }

 

通过构造方式配置Bean

1 <bean id="city" class="com.proc.bean.City">
2     <constructor-arg value="北京"/>
3     <constructor-arg value="BJ"/>
4 </bean>

 

测试代码

1 ApplicationContext ctx=new ClassPathXmlApplicationContext("applicationContext.xml");
2 City city=ctx.getBean("city", City.class);
3 System.out.println(city);

输出结果

City [name=北京, code=BJ]

 

2、静态工厂实例化

　　先创建一个静态工厂StaticCityFactory

 1 package com.proc.bean;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 
 6 public class StaticCityFactory {
 7     
 8     private static Map<String, City> cities;
 9     
10     static{
11         cities=new HashMap<String, City>();
12         cities.put("BJ", new City("北京", "BJ"));
13         cities.put("SH", new City("上海", "SH"));
14         cities.put("CD", new City("成都", "CD"));
15         cities.put("SZ", new City("深圳", "SZ"));
16     }
17 
18     public static City getCity(String code){
19         return cities.get(code);
20     }
21 }

 

　　配置bean

1 <!-- 通过静态工厂实例化对象
2     class:静态工厂类型
3     factory-method:静态工厂静态方法名称
4     constructor-arg:为静态工厂方法指定参数
5  -->
6 <bean id="city" class="com.proc.bean.StaticCityFactory" factory-method="getCity">
7     <constructor-arg value="BJ"/>
8 </bean>

 

3、动态工厂实例化

　　先创建一个实例化工厂

 1 package com.proc.bean;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 
 6 public class InstanceCityFactory {
 7     
 8     private Map<String, City> cities;
 9     {
10         cities=new HashMap<String, City>();
11         cities.put("BJ", new City("北京", "BJ"));
12         cities.put("SH", new City("上海", "SH"));
13         cities.put("CD", new City("成都", "CD"));
14         cities.put("SZ", new City("深圳", "SZ"));
15     }
16     
17     public City getCity(String code){
18         return cities.get(code);
19     }
20 }

　　配置

1 <!-- 配置实例化工厂 -->
2 <bean id="cityFacotry" class="com.proc.bean.InstanceCityFactory"/>
3  
4  <!-- 通过实例化工厂获取对象 -->
5 <bean id="city" factory-bean="cityFacotry" factory-method="getCity">
6     <constructor-arg value="SH"/> <!-- 配置参数 -->
7 </bean>