详解Spring基于xml的两种依赖注入方式

1）使用构造器注入bean

实体类：用户类

public class User {
  private String name;
  private UserMessage userMessage;

  public User() {
  }

  public User(String name, UserMessage userMessage) {
    this.name = name;
    this.userMessage = userMessage;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public UserMessage getUserMessage() {
    return userMessage;
  }

  public void setUserMessage(UserMessage userMessage) {
    this.userMessage = userMessage;
  }

  @Override
  public String toString() {
    return "User{" + "name='" + name + '\'' + ", userMessage=" + userMessage + '}';
  }
}

实体类：用户信息类

public class UserMessage {
  private String username;
  private String password;

  public UserMessage() {
  }

  public UserMessage(String username, String password) {
    this.username = username;
    this.password = password;
  }

  public String getUsername() {
    return username;
  }

  public void setUsername(String username) {
    this.username = username;
  }

  public String getPassword() {
    return password;
  }

  public void setPassword(String password) {
    this.password = password;
  }

  @Override
  public String toString() {
    return "UserMessage{" + "username='" + username + '\'' + ", password='" + password + '\'' + '}';
  }
}

配置文件

<?xml version="1.0" encoding="UTF-8"?>
<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.xsd">

  <!-- 注册UserMessage类 -->
  <bean id="userMessage" class="entity.UserMessage">
    <constructor-arg name="username" value="scott"></constructor-arg>
    <constructor-arg name="password" value="tiger"></constructor-arg>
  </bean>

  <!-- 注册User类 -->
  <bean id="user" class="entity.User">
    <constructor-arg name="name" value="tom"></constructor-arg>
    <constructor-arg name="userMessage" ref="userMessage"></constructor-arg>
  </bean>

</beans>

测试类

public class TestDI {
  @Test
  public void test() {
    ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
    User user = ac.getBean("user", User.class);
    System.out.println(user);
  }
}

测试结果

User{name='tom', userMessage=UserMessage{username='scott', password='tiger'}}

2）使用setter方法注入bean

实体类：用户类

public class User {
  private String name;
  private UserMessage userMessage;

  public User() {
  }

  public User(String name, UserMessage userMessage) {
    this.name = name;
    this.userMessage = userMessage;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public UserMessage getUserMessage() {
    return userMessage;
  }

  public void setUserMessage(UserMessage userMessage) {
    this.userMessage = userMessage;
  }

  @Override
  public String toString() {
    return "User{" + "name='" + name + '\'' + ", userMessage=" + userMessage + '}';
  }
}

实体类：用户信息类

public class UserMessage {
  private String username;
  private String password;

  public UserMessage() {
  }

  public UserMessage(String username, String password) {
    this.username = username;
    this.password = password;
  }

  public String getUsername() {
    return username;
  }

  public void setUsername(String username) {
    this.username = username;
  }

  public String getPassword() {
    return password;
  }

  public void setPassword(String password) {
    this.password = password;
  }

  @Override
  public String toString() {
    return "UserMessage{" + "username='" + username + '\'' + ", password='" + password + '\'' + '}';
  }
}

配置文件

<?xml version="1.0" encoding="UTF-8"?>
<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.xsd">

  <!-- 注册UserMessage类 -->
  <bean id="userMessage" class="entity.UserMessage">
    <property name="username" value="scott"></property>
    <property name="password" value="tiger"></property>
  </bean>

  <!-- 注册User类 -->
  <bean id="user" class="entity.User">
    <property name="name" value="tom"></property>
    <property name="userMessage" ref="userMessage"></property>
  </bean>

</beans>

测试类

public class TestDI {
  @Test
  public void test() {
    ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
    User user = ac.getBean("user", User.class);
    System.out.println(user);
  }
}

测试结果

User{name='tom', userMessage=UserMessage{username='scott', password='tiger'}}

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