Spring属性注入的四种方式（XML）

• set方式注入

  给User对象的name属性注入值

  值类型注入：

  User.java
  package cn.jjs.bean;
  
  public class User {
      public User() {
          System.out.println("User空参构造器");
      }
  
      private String name;
      private Integer age;
  
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
      }
  
      public Integer getAge() {
          return age;
      }
  
      public void setAge(Integer age) {
          this.age = age;
      }
  
      @Override
      public String toString() {
          return "User{" +
                  "name='" + name + '\'' +
                  ", age=" + age +
                  '}';
      }
  }
  

  applicationContext.xml
  
  <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
      
      <bean name="user" class="cn.jjs.bean.User">
          
          <property name="name" value="Tom">property>
          <property name="age" value="18">property>
      bean>
  
  beans>

  Demo.java
  package cn.jjs.c_injection;
  
  import cn.jjs.bean.User;
  import org.junit.Test;
  import org.springframework.context.ApplicationContext;
  import org.springframework.context.support.ClassPathXmlApplicationContext;
  
  public class Demo {
      @Test
      public void Test() {
          //1. 创建容器对象
          ApplicationContext ac = new ClassPathXmlApplicationContext("cn/jjs/c_injection/applicationContext.xml");
          //2. 向容器"要"user对象
          User u = (User) ac.getBean("user");
          //3. 打印对象
          System.out.println(u);
  
      }
  }

  引用类型注入:

  Car.java
  package cn.jjs.bean;
  
  public class Car {
      private String name;
      private String color;
  
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
      }
  
      public String getColor() {
          return color;
      }
  
      public void setColor(String color) {
          this.color = color;
      }
  
      @Override
      public String toString() {
          return "User{" +
                  "name='" + name + '\'' +
                  ", age=" + age +
                  ", car=" + car +
                  '}';
      }
  }

  User.java
  package cn.jjs.bean;
  
  public class User {
      public User() {
          System.out.println("User空参构造器");
      }
  
      private String name;
      private Integer age;
      private Car car;
  
      public Car getCar() {
          return car;
      }
  
      public void setCar(Car car) {
          this.car = car;
      }
  
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
      }
  
      public Integer getAge() {
          return age;
      }
  
      public void setAge(Integer age) {
          this.age = age;
      }
  }

  applicationContext.xml
  
  <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
      
      <bean name="user" class="cn.jjs.bean.User">
          
          <property name="name" value="Tom">property>
          <property name="age" value="18">property>
          <property name="car" ref="carRef">property>
      bean>
  
      
      <bean name="carRef" class="cn.jjs.bean.Car">
          <property name="name" value="Toyota">property>
          <property name="color" value="white">property>
      bean>
  
  beans>

  结果

  User空参构造器
  User{name='Tom', age=18, car=Car{name='Toyota', color='white'}}

• 构造器注入（name, index, type）

  • name属性：构造器的参数名
  • index属性：构造器的参数索引
  • type属性：构造器的参数类型

  生成User(String name, Car car)有参构造器。

  User.java
  package cn.jjs.bean;
  
  public class User {
      public User() {
          System.out.println("User空参构造器");
      }
  
      private String name;
      private Integer age;
      private Car car;
  
      public User(String name, Car car) {
          System.out.println("(String name, Car car)");
          this.name = name;
          this.car = car;
      }
  
      public Car getCar() {
          return car;
      }
  
      public void setCar(Car car) {
          this.car = car;
      }
  
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
      }
  
      public Integer getAge() {
          return age;
      }
  
      public void setAge(Integer age) {
          this.age = age;
      }
  
      @Override
      public String toString() {
          return "User{" +
                  "name='" + name + '\'' +
                  ", age=" + age +
                  ", car=" + car +
                  '}';
      }
  }
  

  
  <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
      
      <bean name="carRef" class="cn.jjs.bean.Car">
          <property name="name" value="Toyota">property>
          <property name="color" value="white">property>
      bean>
  
      
      
      <bean name="user1" class="cn.jjs.bean.User">
          <constructor-arg name="name" value="Tom">constructor-arg>
          <constructor-arg name="car" ref="carRef">constructor-arg>
      bean>
  beans>

  结果

  User空参构造器
  (String name, Car car)
  User{name='Tom', age=null, car=Car{name='Toyota', color='white'}}

  ⚠️

  如果遇到构造器的形参列表相同，顺序不同，比如：

  User.java
  package cn.jjs.bean;
  
  public class User {
      public User() {
          System.out.println("User空参构造器");
      }
  
      private String name;
      private Integer age;
      private Car car;
  
      public User(Car car, String name) {
          this.car = car;
          this.name = name;
      }
      public User(String name, Car car) {
          System.out.println("(String name, Car car)");
          this.name = name;
          this.car = car;
      }
  
      public Car getCar() {
          return car;
      }
  
      public void setCar(Car car) {
          this.car = car;
      }
  
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
      }
  
      public Integer getAge() {
          return age;
      }
  
      public void setAge(Integer age) {
          this.age = age;
      }
  
      @Override
      public String toString() {
          return "User{" +
                  "name='" + name + '\'' +
                  ", age=" + age +
                  ", car=" + car +
                  '}';
      }
  }

  可以通过index

  <bean name="user1" class="cn.jjs.bean.User">
      <constructor-arg name="name" value="Tom" index="0">constructor-arg>
      <constructor-arg name="car" ref="carRef" index="1">constructor-arg>
  bean>

  则选择：

      public User(String name, Car car) {
          System.out.println("(String name, Car car)");
          this.name = name;
          this.car = car;
      }

  这条构造器。

  ⚠️

  如果遇到形参名相同，则：

  User.java
  package cn.jjs.bean;
  
  public class User {
      public User() {
          System.out.println("User空参构造器");
      }
  
      private String name;
      private Integer age;
      private Car car;
      public User(Integer name, Car car) {
          System.out.println("(Integer name, Car car)");
          this.name = name + "";
          this.car = car;
      }
  
      public User(String name, Car car) {
          System.out.println("(String name, Car car)");
          this.name = name;
          this.car = car;
      }
  
      public Car getCar() {
          return car;
      }
  
      public void setCar(Car car) {
          this.car = car;
      }
  
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
      }
  
      public Integer getAge() {
          return age;
      }
  
      public void setAge(Integer age) {
          this.age = age;
      }
  
      @Override
      public String toString() {
          return "User{" +
                  "name='" + name + '\'' +
                  ", age=" + age +
                  ", car=" + car +
                  '}';
      }
  }
  

  需要通过给出完整类名type属性，定位构造器。

  <bean name="user1" class="cn.jjs.bean.User">
         <constructor-arg name="name" value="Tom" index="0" type="java.lang.Integer">     constructor-arg>
         <constructor-arg name="car" ref="carRef" index="1">constructor-arg>
  bean>

• p名称空间注入

  导入p名称空间

  <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

  使用 p: 完成注入：

  • 值类型： p:属性名=“值”;
  • 引用类型：p:属性名-ref=”bean名称”;

  
  <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
  
      
      <bean name="carRef" class="cn.jjs.bean.Car">
          <property name="name" value="Toyota">property>
          <property name="color" value="white">property>
      bean>
  
      <bean name="user2" class="cn.jjs.bean.User" p:name="jack" p:age="30" p:car-ref="carRef">bean>
  beans>

  本质是set注入。

  • #### SPEL表达式注入（Spring Expression Language ） #{bean名称 . property名称}

  applicationContext.xml
  
  <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
  
      <bean name="user" class="cn.jjs.bean.User">
          
          <property name="name" value="Tom">property>
          <property name="age" value="18">property>
          <property name="car" ref="carRef">property>
      bean>
  
      
      <bean name="carRef" class="cn.jjs.bean.Car">
          <property name="name" value="Toyota">property>
          <property name="color" value="white">property>
      bean>
  
      <bean name="user2" class="cn.jjs.bean.User" p:name="jack" p:age="30" p:car-ref="carRef">bean>
  
      <bean name="user3" class="cn.jjs.bean.User">
          <property name="name" value="#{user.name}">property>
          <property name="age" value="#{user2.age}">property>
          <property name="car" ref="carRef">property>
      bean>
  beans>