Mybatis需要注意的细节，

mybatis第二篇

1.${}和#{}的区别

1.#在传参的时候，会自动拼接单引号；$不能拼接单引号;

2.$传参时，一般不支持jdbcType指定类型的写法;#则可以;如:
​ #{name,jdbcType=VARCHAR}
3.$一般用于在sql中拼接表名，结果排序，模糊查询等操作;其他正常参数传递一般使用
4.因为${}使用后不会自动拼接单引号，所以可能还会导致sql攻击

select * from user where username=${username} and password=${username}

当输入值为" ‘ttt' or '22'='22' ”时，sql就被替换为

select * from user where username='ttt' or '22'='22' and password='ttt'  or '22'='22'

2.在插入数据时获取主键

<!-- 增加 -->
<insert id="insert" parameterType="cn.sz.gl.pojo.Users" >
    insert into users(id,name,password)
    values(users_seq.nextval, #{name,jdbcType=VARCHAR}, 
    #{password,jdbcType=VARCHAR})
</insert>

这里提供两种方案

3.ThreadLocal本地线程的使用

现编写工具类MySqlSessionFactory.java

public class MySqlSessionFactory {
    private static final String RESOURCE = "mybatis_config.xml";
    private static SqlSessionFactoryBuilder builder = null;
    private static SqlSessionFactory factory = null;
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    static{
        try {
            InputStream is = Resources.getResourceAsStream(RESOURCE);
            builder = new SqlSessionFactoryBuilder();
            factory = builder.build(is);
        } catch (IOException e) {
            System.out.println("加载配置文件.....");
        }
    }
    
    
    public static SqlSession getMySqlSession() {
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession==null) {
            sqlSession = factory.openSession();
            threadLocal.set(sqlSession);
        }
        return sqlSession;
    }
    public static void closeSqlSession() {
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession!=null) {
            sqlSession.close();
        }
        threadLocal.set(null);
    }
    
}

使用在service中

public class UsersServiceImpl implements UsersService {
    private static SqlSession sqlsession
                =MySqlSessionFactory.getMySqlSession();
    private UsersDao dao = null;
    
    /**
     * 查询全部
     * @return
     */
    public List<Users> findAll(){
        try {
            dao=sqlsession.getMapper(UsersDao.class);
            return dao.findAll();
        } catch (Exception e) {
            System.out.println("findAll'查询列表失败！");
            
        }
        return Collections.EMPTY_LIST;
    }
}

测试

public class UsersServiceImplTest {
    private UsersService service=null;
    @Before
    public void init() {
        service=new UsersServiceImpl();
    }       
    
    @Test
    public void testFindAll() {
        
        service.findAll().forEach(System.out::println);
    }
}