mybatis相关疑惑

[TOC]

mybatis中#和$的区别

#{parameterName}

${parameterName}

首先，我们说一下这两种引用参数时的区别，使用#{parameterName}引用参数的时候，Mybatis会把这个参数认为是一个字符串，并自动加上’’，例如传入参数是“Smith”，那么在下面SQL中：

1	Select * from emp where name = #{employeeName}

使用的时候就会转换为：

1	Select * from emp where name = 'Smith';

同时使用${parameterName}的时候在下面SQL中

1	Select * from emp where name = ${employeeName}

就会直接转换为：

1	Select * from emp where name = Smith

简单说#{}是经过预编译的,是安全的。

而${}是未经过预编译的,仅仅是取变量的值,是非安全的,存在SQL注入。

1 2	#{} 这种取值是编译好SQL语句再取值 ${} 这种是取值以后再去编译SQL语句

下面我们用一个实际的例子看看分别使用和是否可以防止SQL注入。

首先是使用#{}：

<!-- 使用#{} -->
  <select id="selectUser" parameterType="String" 
    resultType="com.mybatis.po.MyUser">
    select * from user where account = #{account} and password = #{password}
  </select>

分别测试正常传参和拼接传参：

// 使用#{} 正常传参
    Map<String, Object> parameter = new HashMap<>();
    parameter.put("account", );
    parameter.put("password", password);
    MyUser mu = ss.selectOne("com.mybatis.mapper.UserMapper.selectUser", parameter);
    System.out.println("返回结果：" + mu);
    
    // 使用#{} 拼接传参
    Map<String, Object> parameter_1 = new HashMap<>();
    parameter_1.put("account", "201301001");
    parameter_1.put("password", "111111" + "or account = 'admin' ");
    MyUser mu_1 = ss.selectOne("com.mybatis.mapper.UserMapper.selectUser", parameter_1);
    System.out.println("返回结果：" + mu_1);

结果如下：

DEBUG [http-nio-8080-exec-5] - ==>  Preparing: select * from user where account = ? and password = ? 
DEBUG [http-nio-8080-exec-5] - ==> Parameters: 201301001(String), 111111(String)
DEBUG [http-nio-8080-exec-5] - <==      Total: 1
返回结果：MyUser [id=17, account=201301001, password=111111, name=蒙奇D路飞]
DEBUG [http-nio-8080-exec-5] - ==>  Preparing: select * from user where account = ? and password = ? 
DEBUG [http-nio-8080-exec-5] - ==> Parameters: 201301001(String), 111111 or account = 'admin' (String)
DEBUG [http-nio-8080-exec-5] - <==      Total: 0
返回结果：null

很明显，使用#{}的时候，即使传入了恶意参数，#{}只会将其作为一个占位符的参数，如上面这个例子：

DEBUG [http-nio-8080-exec-5] - ==>  Preparing: select * from user where account = ? and password = ? 
DEBUG [http-nio-8080-exec-5] - ==> Parameters: 201301001(String), 111111 or account = 'admin' (String)
DEBUG [http-nio-8080-exec-5] - <==      Total: 0
转换为实际的SQL语句：select * from user where account = '201301001' and password = '111111 or account = 'admin''

1 2	select * from user where account = '201301001' and password = '111111 or account = 'admin'' select * from user where account = 201301001 and password = 111111 or account = 'admin'

现在是使用${}：

<!-- 使用${} -->
  <select id="selectUser2" parameterType="String" 
    resultType="com.mybatis.po.MyUser">
    select * from user where account = ${account} and password = ${password}
  </select>

分别测试正常传参和拼接传参：

// 使用${} 正常传参
    Map<String, Object> parameter = new HashMap<>();
    parameter.put("account", "201301001");
    parameter.put("password", "111111");
    MyUser mu = ss.selectOne("com.mybatis.mapper.UserMapper.selectUser2",parameter);
    System.out.println("返回结果：" + mu);

   // 使用${} 拼接传参
   Map<String, Object> parameter2 = new HashMap<>();
   parameter2.put("account", "201301001");
   parameter2.put("password", "111111" + " or account = 'admin' ");
   MyUser mu2 = ss.selectOne("com.mybatis.mapper.UserMapper.selectUser2", parameter2);
   System.out.println("返回结果：" + mu2);

结果如下：

DEBUG [http-nio-8080-exec-18] - ==>  Preparing: select * from user where account = 201301001 and password = 111111 
DEBUG [http-nio-8080-exec-18] - ==> Parameters: 
DEBUG [http-nio-8080-exec-18] - <==      Total: 1
返回结果：MyUser [id=17, account=201301001, password=111111, name=蒙奇D路飞]
DEBUG [http-nio-8080-exec-18] - ==>  Preparing: select * from user where account = 201301001 and password = 111111 or account = 'admin' 
DEBUG [http-nio-8080-exec-18] - ==> Parameters: 
DEBUG [http-nio-8080-exec-18] - <==      Total: 2
返回结果：[MyUser [id=1, account=admin, password=111111, name=管理员], MyUser [id=17, account=201301001, password=111111, name=蒙奇D路飞]]

很明显，使用${}将参数拼接后在编译成SQL语句，不能防止SQL注入，查询出了有关account=admin的额外信息，这是很危险的。

返回主键id

insert into test(name,descr,url,create_time,update_time) values(#{name},#{descr},#{url},now(),now())