spring依賴注入的方式有4種

• 構造方法注入
• 屬性注入
• 工廠注入
• 注解注入

下面通過一個實例統一講解：

User.java

package com.bjsxt.model;public class User {    private String username;    private String passWord;    public User(){}    public User(String username, String password) {        super();        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 "User [username=" + username + ", password=" + password + "]";    }}

UserDAO.java

package com.bjsxt.dao;import com.bjsxt.model.User;public interface UserDAO {    public void save(User user);}

UserDAO實現類UserDAOImpl

package com.bjsxt.dao.impl;import com.bjsxt.dao.UserDAO;import com.bjsxt.model.User;public class UserDAOImpl implements UserDAO {    public void save(User user) {        //Hibernate        //JDBC        //xml        //NetWork        System.out.println("user saved!");    }}

工廠類

第一個：UserFactory

package com.bjsxt.factory;import com.bjsxt.model.User;public class UserFactory {    public User CreatUser () {        User user=new User();        user.setUsername("周1");        user.setPassword("oumyye");        return user;    }}

第二個：UserFactory2 

package com.bjsxt.factory;import com.bjsxt.model.User;public class UserFactory2 {    public static User CreatUser () {        User user=new User();        user.setUsername("偶my耶1");        user.setPassword("oumyye");        return user;    }}

控制層：UserService

package com.bjsxt.service;import com.bjsxt.dao.UserDAO;import com.bjsxt.model.User;public class UserService {        private UserDAO userDAO;          public void init() {        System.out.println("###########init");    }        public void save(User user) {        userDAO.save(user);    }    public UserDAO getUserDAO() {        return userDAO;    }    public void setUserDAO(UserDAO userDAO) {        this.userDAO = userDAO;    }        public UserService(UserDAO userDAO) {        super();        this.userDAO = userDAO;    }        public void destroy() {        System.out.println("destroy");    }}

配置文件：bean.xml

<?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-2.5.xsd">    <!--        構造方法注入 -->    <bean id="user" class="com.bjsxt.model.User" >    <constructor-arg index="0" type="String" value="zhou"></constructor-arg>    <constructor-arg index="1" type="String" value="password"></constructor-arg>    </bean>        <!-- 屬性注入 -->    <bean id="user1" class="com.bjsxt.model.User" >    <property name="username" value="zhang"></property>    <property name="password" value="oumyye"></property>    </bean>    <!-- 工廠注入 -->    <bean  id= "userFactory" class="com.bjsxt.factory.UserFactory" > </bean>    <bean id="user2" factory-bean="userFactory" factory-method="CreatUser"></bean>        <!-- 靜態工廠注入 -->    <bean  id= "user3" class="com.bjsxt.factory.UserFactory2" factory-method="CreatUser"> </bean>          <bean id="u" class="com.bjsxt.dao.impl.UserDAOImpl"></bean>           <bean id="userService" class="com.bjsxt.service.UserService" init-method="init" destroy-method="destroy" scope="prototype">            <!-- <property name="userDAO" ref="u" /> -->      <!--        構造方法注入 -->       <constructor-arg>           <ref bean="u"/>       </constructor-arg>  </bean>  </beans>

測試類：

package com.bjsxt.service;import static org.junit.Assert.*;import org.junit.Test;import org.springframework.context.applicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import com.bjsxt.model.User;public class UserServiceTest {    @Test    public void test() {        ApplicationContext applicationContext=new ClassPathXmlApplicationContext("beans.xml");        UserService userService=(UserService) applicationContext.getBean("userService");        //構造方法注入        User user=(User) applicationContext.getBean("user");        //屬性注入        User user1=(User) applicationContext.getBean("user1");        //工廠注入        User user2=(User) applicationContext.getBean("user2");        //工廠注入        User user3=(User) applicationContext.getBean("user3");                System.out.println(user);        System.out.println(user1);        System.out.println(user2);        System.out.println(user3);        userService.save(user);        userService.destroy();    }}

結果：

###########initUser [username=zhou, password=password]User [username=zhang, password=oumyye]User [username=周1, password=oumyye]User [username=偶my耶1, password=oumyye]user saved!destroy

注解方式在后面詳細介紹

Spring中提供了自動裝配依賴對象的機制，但是在實際應用中并不推薦使用自動裝配，因為自動裝配會產生未知情況，開發人員無法預見最終的裝配結果。

自動裝配是在配置文件中實現的，如下：

<beanid="***"class="***"autowire="byType">

只需要配置一個autowire屬性即可完成自動裝配，不用再配置文件中寫<property>,但是在類中還是要生成依賴對象的setter方法。

Autowire的屬性值有如下幾個：

·byType按類型裝配可以根據屬性類型，在容器中尋找該類型匹配的bean，如有多個，則會拋出異常，如果沒有找到，則屬性值為null；

·byName按名稱裝配可以根據屬性的名稱在容器中查詢與該屬性名稱相同的bean，如果沒有找到，則屬性值為null；

·constructor與byType方式相似，不同之處在與它應用于構造器參數，如果在容器中沒有找到與構造器參數類型一致的bean，那么將拋出異常；

·autodetect通過bean類的自省機制(introspection)來決定是使用constructor還是byType的方式進行自動裝配。如果發現默認的構造器，那么將使用byType的方式。