Spring的applicationContext默认使用无参构造创建对象

 1 public class User {
 2     private String name;
 3 　　
 4     public User() {
 5         System.out.println("User的无参构造");
 6睿共享     }
 7 
 8     pu睿共享blic String getName() {
 9         return name;
10     }
11 
12     public void setName(String name) {
13         this.name = name;
14     }
15 
16 }

 1 "1.0" encoding="UTF-8"?>
 2 "http://www.springframework.org/schema/beans"
 3        xmlns_xsi="http://www.w3.org/2001/XMLSchema-instance"
 4        xsi_schemaLocation="http://www.springframework.org/schem睿共享a/beans
 5         https://www.springframework.org/schema/beans/spring-beans.xsd">
 6     "user" class="com.rzk.pojo.User">
 7         "name" value="小明"/>默认使用无参设置值
 8     
 9 
10 
11

1 public class Mytext {
2     public static void main(String[] args) {
3         ApplicationContext context = new ClassPathXmlApplicatio睿共享nContext("applicationContext.xml");
4         User user = (User) context.getBean("user");
5         
6 　　　　　application一注册就实例化
7     }
8 }

当我们创建ApplicationContext对象的时候同时会将配置文件中配置的bean对象一起创建

（饿汉模式）这时候无参构造也被加载

上面是使用无参设置值

下面是有参设置

 1 public class User {
 2     private String name;
 3 
 4     public User(String name) {
 5         this.name = name;
 6         System.out.println("User的有参构造");
 7     }
 8 
 9     public String getName() {
10         return name;
11     }
12 
13     public void setName(String name) {
14         this.name = name;
15     }
16 
17 }

直接通过参数名设置值

 1  "1.0" encoding="UTF-8"?>
 2  "http://www.springframework.org/schema/beans"
 3         xmlns_xsi="http://www.w3.org/2001/XMLSchema-instance"
 4         xsi_schemaLocation="http://www.springframework.org/schema/beans
 5          https://www.springframework.org/schema/beans/spring-beans.xsd">
 6      "user" class="com.rzk.pojo.User">
 7  
 8          "name"  value="小明" />使用有参注入值
 9      
10

通过下标赋值

 1 public class User {
 2     private String name;
 3     private int age;
 4 
 5     public User(String name, int age) {
 6         this.name = name;
 7         this.age = age;
 8         System.out.println("User的有参构造");
 9     }
10 
11     public String getName() {
12         return name;
13     }
14 
15     public void setName(String name) {
16         this.name = name;
17     }
18 
19     public int getAge() {
20         return age;
21     }
22 
23     public void setAge(int age) {
24         this.age = age;
25     }
26 }

 1 "1.0" encoding="UTF-8"?>
 2 "http://www.springframework.org/schema/beans"
 3        xmlns_xsi="http://www.w3.org/2001/XMLSchema-instance"
 4        xsi_schemaLocation="http://www.springframework.org/schema/beans
 5         https://www.springframework.org/schema/beans/spring-beans.xsd">
 6     "user" class="com.rzk.pojo.User">
 7         "0"  valu睿共享e="小明" />
 8         "1" value="12"/>
 9     
10

Spring的applicationContext默认使用无参构造创建对象

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