spring快速入门-注解

用一个词就可以描述注解，那就是元数据，即一种描述数据的数据。所以，可以说注解就是源代码的元数据。可以理解为一种标记。

简化开发

@Component
@Service
@Controller
@Reposity
上面四个注解都是用于标记Bean的实体类，用于spring容器能够在创建Bean时，能找到对应的实体类进行Bean的初始化，其中@component的作用范围最大


@Autowired 自动装配通过类型，名字

@Autowired顾名思义，就是自动装配，其作用是为了消除代码Java代码里面的getter/setter与bean属性中的property。当然，getter看个人需求，如果私有属性需要对外提供的话，应当予以保留。@Autowired默认按类型匹配的方式，在容器查找匹配的Bean，当有且仅有一个匹配的Bean时，Spring将其注入@Autowired标注的变量中。

如果不唯一通过@Qualifier获取

@Resource: 自动装配通过名字，类型
 
@Configuration 标记该类为配置类
@ComponentScan 扫描指定类或包

 
    
        org.springframework
        spring-webmvc
        5.3.3
    

package pojo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class Teacher {
    @Value("Jerry")//动态将值注入
    private String name;
    @Value("12")
    private Integer age;

    public Teacher() {
    }

    public Teacher(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

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

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Teacher{" +
                "name='" + name + ''' +
                ", age=" + age +
                '}';
    }
}

package pojo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.stereotype.Component;

@Component
public class Student {
    @Value("tom")
    private String name;
    @Value("12")
    private Integer age;
    private Teacher teacher;

    public Student() {
    }

    @Autowired
    @Qualifier("teacher1")
    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    public Student(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

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

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + ''' +
                ", age=" + age +
                ", teacher=" + teacher +
                '}';
    }
}

@Test
    public void test5(){
        ApplicationContext context = new ClassPathXmlApplicationContext("bean2.xml");
        Student student = context.getBean("student", Student.class);
        System.out.println(student);
    }
    

不使用配置文件

• 创建注解类

• package config;
  
  import method.UserDAO;
  import method.UserDAOImpl;
  import org.springframework.context.annotation.Bean;
  import org.springframework.context.annotation.ComponentScan;
  import org.springframework.context.annotation.Configuration;
  import pojo.Student;
  import pojo.Teacher;
  
  @Configuration
  @ComponentScan({"pojo","method"})
  public class springConfig {
      @Bean
      public UserDAO getUserDAO(){
          return new UserDAOImpl();
      }
      @Bean
      public Student student(){
          return new Student();
      }
      @Bean
      public Teacher teacher1(){
          return new Teacher();
      }
  
  }
  

@Test
    public void test4(){
        BeanFactory context = new AnnotationConfigApplicationContext(springConfig.class);
        Student student = context.getBean("student", Student.class);
        System.out.println(student);
    }