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SpringIOC注解方式之自动装配.md

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SpringIOC注解方式之自动装配（@Autowired）

一、自动装配

  • 使用注解使ioc容器维护bean，但是bean之间的关联关系我们可以使用 @Autowired , 此注解可以写在属性上，构造方法上，setter方法上

  • @resource @Inject 和@Autowired用法功能类似，功能不全，建议使用@Autowired

  • spring容器会首先根据变量名 = bean的id名(此处id必须是手动指定的，默认的不行)去匹配，如果匹配不上再根据类型查找容器中相应的bean进行关联

    eg:

    @Autowired
private StudentDao studentDao;
//首先比对id名和变量名是否相同，比对不上就选类名去填补。

  • 默认容器中必须有匹配bean，如果允许可以没有此类型的bean，那么可以@Autowired(required=false)

  • 如果容器中按类型匹配有多个匹配类型，我们一般可以使用@Qualifier,后边必须指出所需id。

    eg:

    @Autowired
@Qualifier(value = "studentDaoImpl2")
private StudentDao studentDao;
//@Qualifier：指定所需的id

//或：
@Autowired
@Qualifier("studentDAOImpl")
private StudentDAO studentDAO;

//或：
@Autowired
@Qualifier("studentDAOImpl")
public void setStudentDAO(StudentDAO studentDAO) {
    this.studentDAO = studentDAO;
}

//或：
@Autowired
public void setStudentDAO(@Qualifier("studentDAOImpl")StudentDAO studentDAO) {
    this.studentDAO = studentDAO;
}

二、应用

  • dao层

    StudentDao接口

    package com.edu.dao;

public interface StudentDao {
    int insert();
}

    StudentDaoImpl类

    package com.edu.dao.impl;

import com.edu.dao.StudentDao;
import org.springframework.stereotype.Repository;

//@Repository
//@Repository(value = "studentDao")
//@Repository("studentDao")
@Repository //持久层
public class StudentDaoImpl implements StudentDao {

    @Override
    public int insert() {
        System.out.println("增加一个学生");
        return 1;
    }
}

    StudentDaoImpl2类

    package com.edu.dao.impl;

import com.edu.dao.StudentDao;
import org.springframework.stereotype.Repository;

@Repository//持久层
public class StudentDaoImpl2 implements StudentDao {
    @Override
    public int insert() {
        System.out.println("又一个实现类：增加一个学生");
        return 1;
    }
}

  • service层

    StudentService接口

    package com.edu.service;

public interface StudentService {
    int insert();
}

    StudentServiceImpl类

    package com.edu.service.impl;

import com.edu.dao.StudentDao;
import com.edu.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

@Service//业务层
public class StudentServiceImpl implements StudentService {

//    @Autowired
//    private StudentDao studentDao;//当studentDao接口只有一个实现类时
    
    @Autowired
    @Qualifier(value = "studentDaoImpl2")
    private StudentDao studentDao;

//    @Autowired
//    private StudentDao studentDaoImp;

//    @Autowired
//    private StudentDao studentDaoImpl2;

    @Override
    public int insert() {
        return studentDao.insert();
    }
}

  • 配置xml

    <context:component-scan base-package="com.edu"/>

  • 测试

    package com.edu;

import com.edu.service.StudentService;
import com.edu.service.impl.StudentServiceImpl;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class AutoTest {
    @Test
    public void testAuto(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring.xml");
        StudentService service = applicationContext.getBean(StudentServiceImpl.class);
        service.insert();
    }
}

  • 总结：

    当使用 @Autowired                     时，首先检测  studentDao（变量名）与 bean的id  是否匹配，
      private StudentDao studentDao;  
如果匹配不上再根据类型查找容器中相应的bean进行关联。若该类型存在多个相应的bean，则使用
@Autowired
private StudentDao studentDaoImp;
//或
@Autowired
private StudentDao studentDaoImpl2;
//或
@Autowired
@Qualifier(value = "studentDaoImpl2")
private StudentDao studentDao;
去指定。

//或
@Repository("studentDao") //持久层
public class StudentDaoImpl implements StudentDao {

}
//或
@Repository("studentDao") //持久层
public class StudentDaoImpl2 implements StudentDao {

}