spring 依赖注入 set和构造方法

package com.ligy.service;

import com.ligy.dao.StudentDao;
import com.ligy.dao.TeacherDao;
import com.ligy.dao.TeacherDaoImpl;

public class TeacherServiceImpl implements ITeacherService {

    private TeacherDao teacherDao;

//    public void setTeacherDao(TeacherDao teacherDao) {
//        this.teacherDao = teacherDao;
//    }
//
//    public TeacherServiceImpl() {
//
//    }

    public TeacherServiceImpl(TeacherDao teacherDao) {
        this.teacherDao = teacherDao;
    }

    @Override
    public void add() {
        this.teacherDao.add();
        System.out.println("this is in StudentServiceImpl do1");
    }
}

<?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:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.2.xsd">
    <!-- 由 Spring容器创建该类的实例对象 -->
    <bean id="studentDao" class="com.ligy.dao.StudentDaoImpl"/>
    <bean id="teacherDao" class="com.ligy.dao.TeacherDaoImpl"/>
    <bean id="StudentService" class="com.ligy.service.StudentServiceImpl">
        <property name="studentDao" ref="studentDao"></property>
    </bean>

    <bean id="TeacherService" class="com.ligy.service.TeacherServiceImpl">
        <constructor-arg ref="teacherDao"/>
        <!--<property name="teacherDao" ref="teacherDao"></property>-->
    </bean>

</beans>