自动装配方式分为：no、byName、byType、constructor四种，默认为no
package com.bebig.service;

import com.bebig.dao.UserDAO;
import com.bebig.model.User;
//逻辑业务层
public class UserService {
    private UserDAO userDAO;

    public void add(User u) {
        userDAO.save(u);

    }

    public void setUserDAO(UserDAO userDAO) {
        this.userDAO = userDAO;
    }

    public UserDAO getUserDAO() {
        return userDAO;
    }
}
beans.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" xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context-3.0.xsd"
    <!-- 指定本beans里所有bean的默认自动装配方式 -->
    default-autowire="byName">

    <!-- a service object; we will be profiling its methods -->

    <bean name="userDAO" class="com.bebig.dao.impl.UserDAOImpl">
        <property name="daoId" value="1"></property>
    </bean>
    
    <bean name="u2" class="com.bebig.dao.impl.UserDAOImpl">
        <property name="daoId" value="1"></property>
    </bean>
    <!-- 按指定方式装配 -->
    <bean id="userService" class="com.bebig.service.UserService"
        scope="prototype" autowire="byType">
    </bean>

</beans>