mybatis中，如何用java注解方式实现sql语句查询？

简介: mylbatis除了xml方式实现sql语句动态查询外，用java注解的方式也可以实现，即将sql作为注解参数，在主类中，直接调用接口方法，即相当于调用了查询语句。

1. 总体步骤：
1）建立sql语句注解接口。
2）mybatis-config.xml添加<mapper class = "注解类路径">
3）main方法中，根据sqlSession传入注解类.class，拿到注解类引用，调用响应sql语句。

1）建立注解类

package com.how2java.mapper;

import java.util.List;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import com.how2java.pojo.Category;

public interface CategoryMapper {
    @Insert("insert into Category_ (name) values(#{name})")
    public int add(Category category);
    
    @Select("select * from Category_ where id = #{id}")
    public Category select(int id);
    
    @Delete("delete from Category_ where id = #{id}")
    public void delete(int id);
    
    @Update("update Category_ set name = #{name} where id = #{id}")
    public Category update(Category category);
    
    public List<Category> list();
}

2)配置文件添加注解类映射

<mappers>
        <mapper resource = "com/how2java/pojo/Category.xml"/>
        <mapper class = "com.how2java.mapper.CategoryMapper"/> 
    </mappers>

3）main方法进行测试

package com.how2java.test;

import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.how2java.mapper.CategoryMapper;
import com.how2java.pojo.Category;

public class TestMybatis2 {
    public static void main(String[] args) throws Exception{
        String source = "mybatis-config.xml";
        InputStream stream = Resources.getResourceAsStream(source);
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(stream);
        SqlSession session = sessionFactory.openSession();
        CategoryMapper mapper = session.getMapper(CategoryMapper.class);
        
        update(mapper);
        select(mapper);
        delete(mapper);
        add(mapper);
        
        session.commit();
        session.close();
    }
    
    private static void update(CategoryMapper mapper) {
        Category category = mapper.select(3);  //注解类接口引用直接调用注解方法，相当于执行sql语句。
        System.out.println(category.getName());
        category.setName("newname");
        mapper.update(category);
        listAll(mapper);
        
    }
    
    private static void select(CategoryMapper mapper) {
        Category c = mapper.select(4);
        System.out.println(c.getId() + c.getName());
    }
    
    private static void delete(CategoryMapper mapper) {
        mapper.delete(2);
        listAll(mapper);
    }
    
    private static void add(CategoryMapper mapper) {
        Category c = new Category();
        c.setName("new name");
        mapper.add(c);
        
        listAll(mapper);
    }
    
    private static void listAll(CategoryMapper mapper) {
        List<Category> list= mapper.list();
        for(Category c: list) {
            System.out.println(c.getId() + c.getName());
        }
    }   
}