mybatis详解-(14)参数处理#和$

骑猪看日落 2022-06-03 03:45 385阅读 0赞

前面演示了Mybatis的部分属性，在操作数据库的时候sql中参数的传递都是使用`#{}`，其实Mybatis还提供了`${}`处理参数的方式，也经常被使用。但是使用`#{}`和`${}`到底有什么区别呢，这篇做一个对比，主要以例子查看差别。

# 1.创建实体类 #

Employee

package org.mybatis.dealParams;
    import org.apache.ibatis.type.Alias;
    @Alias("empp")
    public class Employee { 
        private Integer id;
        private String lastName;
        private String email;
        private String gender;
    
        public Integer getId() {
            return id;
        }
        public void setId(Integer id) {
            this.id = id;
        }
        public String getLastName() {
            return lastName;
        }
        public void setLastName(String lastName) {
            this.lastName = lastName;
        }
        public String getEmail() {
            return email;
        }
        public void setEmail(String email) {
            this.email = email;
        }
        public String getGender() {
            return gender;
        }
        public void setGender(String gender) {
            this.gender = gender;
        }
        @Override
        public String toString() {
            return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email
                    + ", gender=" + gender + "]";
        }
    }

# 2.创建接口类 #

EmployeeMapper

package org.mybatis.dealParams;
    
    import org.apache.ibatis.annotations.Param;
    
    public interface EmployeeMapper { 
    
        public Employee getEmpById(Integer id);
    
        public Employee getEmpByIdAndLastName(@Param("id")Integer id,@Param("lastName")String lastName);
    
    }

# 3.创建mapper映射文件 #

dealparamsmapper.xml  
这里参数传递全部使用`#{}` 传递。

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    
    <mapper namespace="org.mybatis.dealParams.EmployeeMapper">
    
        <select id="getEmpById" resultType="empp">
            select id,last_name,email,gender from mybatis_employee where id = #{id}
        </select>
    
        <select id="getEmpByIdAndLastName" resultType="empp">
            select id,last_name,email,gender from mybatis_employee where id = #{id} and last_name like #{lastName}
        </select>
    </mapper>

# 4.创建主配置文件 #

mybatis-config-dealparams.xml，引用mapper配置文件

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
    
        <properties resource="db.properties"></properties>
    
        <settings>
            <setting name="mapUnderscoreToCamelCase" value="true"/>
        </settings>
    
        <typeAliases>
            
            <package name="org.mybatis.dealParams"/>
        </typeAliases>
    
    
        
        <environments default="dev_mysql">
            <environment id="dev_mysql">
                <transactionManager type="JDBC" />
                <dataSource type="POOLED">
                    <property name="driver" value="${mysql.driver}" />
                    <property name="url" value="${mysql.url}" />
                    <property name="username" value="${mysql.username}" />
                    <property name="password" value="${mysql.password}" />
                </dataSource>
            </environment>
    
            <environment id="test_mysql">
                <transactionManager type="JDBC"></transactionManager>
                <dataSource type="POOLED">
                    <property name="driver" value="${mysql.drivertest}" />
                    <property name="url" value="${mysql.urltest}" />
                    <property name="username" value="${mysql.usernametest}" />
                    <property name="password" value="${mysql.passwordtest}" />
                </dataSource>
            </environment>
        </environments> 
        <mappers>
            <mapper resource="mapper/dealparamsmapper.xml"/>
        </mappers>
    </configuration>

# 5.创建测试类 #

在测试类中调用getEmpByIdAndLastName(2, “%li%”)方法，传递id为2，lastName为%li%进行查询。

package org.mybatis.dealParams;
    
    import java.io.IOException;
    import java.io.InputStream;
    
    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 org.junit.Test;
    
    /** * 使用接口式編程 */
    public class MybatisTest { 
    
        @Test
        public void testMybatis() {
            String resource = "mybatis-config-dealparams.xml";//全局配置文件
    
            InputStream inputStream = null;
            SqlSessionFactory sqlSessionFactory = null;
            SqlSession sqlSession = null;
            try {
                inputStream = Resources.getResourceAsStream(resource);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
                sqlSession = sqlSessionFactory.openSession();
    
                EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
                Employee emp = mapper.getEmpByIdAndLastName(2, "%li%");
                System.out.println(emp);
    
                sqlSession.close();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
            }
        }
    }

执行结果如下：

> DEBUG - ooo Using Connection \[com.mysql.jdbc.JDBC4Connection@4232c52b\]  
> DEBUG - ==> Preparing: select id,last\_name,email,gender from mybatis\_employee where id = ? and last\_name like ?  
> DEBUG - ==> Parameters: 2(Integer), %li%(String)  
> Employee \[id=2, lastName=lisi, email=tang\_greatman@qq.com, gender=2\]  
> DEBUG - Resetting autocommit to true on JDBC Connection \[com.mysql.jdbc.JDBC4Connection@4232c52b\]  
> DEBUG - Closing JDBC Connection \[com.mysql.jdbc.JDBC4Connection@4232c52b\]  
> DEBUG - Returned connection 1110623531 to pool.

由打印的结果可以看到执行的sql语句使用的是预编译的形式处理。

# 6.使用$处理参数 #

将`#{id}` 改成`${id}` 进行处理：

<select id="getEmpByIdAndLastName" resultType="empp">
            select id,last_name,email,gender from mybatis_employee where id = ${id} and last_name like #{lastName}
        </select>

执行结果如下：

> DEBUG - ooo Using Connection \[com.mysql.jdbc.JDBC4Connection@58c1670b\]  
> DEBUG - ==> Preparing: select id,last\_name,email,gender from mybatis\_employee where id = 2 and last\_name like ?  
> DEBUG - ==> Parameters: %li%(String)  
> Employee \[id=2, lastName=lisi, email=tang\_greatman@qq.com, gender=2\]  
> DEBUG - Resetting autocommit to true on JDBC Connection \[com.mysql.jdbc.JDBC4Connection@58c1670b\]  
> DEBUG - Closing JDBC Connection \[com.mysql.jdbc.JDBC4Connection@58c1670b\]  
> DEBUG - Returned connection 1489069835 to pool.

由结果可以看出这里使用的是sql拼接的方式进行处理的。

两种方式都可以参数的处理，不难发现第一种不会出现sql注入，第二种方式会出现sql注入的情况。那么第二种方式又有什么存在的价值呢？

其实使用`${}` 方式对于处理分库分表的情况是必不可少的是`#{}`无法替代的。  
比如有很多的订单表，2015\_order\_info,2016\_order\_info,2017\_order\_info等多张订单表，如果想按照年份查询订单数据该怎么处理呢？

这里做一个演示：

添加getEmpByIdAndLastNameAndTableName方法：

public Employee getEmpByIdAndLastNameAndTableName(@Param("tableName")String tableName,@Param("id")Integer id,@Param("lastName")String lastName);

拼接表名：

<select id="getEmpByIdAndLastNameAndTableName" resultType="empp">
            select id,last_name,email,gender from ${tableName}_employee where id = #{id} and last_name like #{lastName}
        </select>

测试：

@Test
        public void testMybatis() {
            String resource = "mybatis-config-dealparams.xml";//全局配置文件
    
            InputStream inputStream = null;
            SqlSessionFactory sqlSessionFactory = null;
            SqlSession sqlSession = null;
            try {
                inputStream = Resources.getResourceAsStream(resource);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
                sqlSession = sqlSessionFactory.openSession();
    
                EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
    // Employee emp = mapper.getEmpByIdAndLastName(2, "%li%");
                Employee emp = mapper.getEmpByIdAndLastNameAndTableName("mybatis", 2, "%li%");
                System.out.println(emp);
    
                sqlSession.close();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
            }
        }

执行结果：

> DEBUG - ooo Using Connection \[com.mysql.jdbc.JDBC4Connection@58c1670b\]  
> DEBUG - ==> Preparing: select id,last\_name,email,gender from mybatis\_employee where id = ? and last\_name like ?  
> DEBUG - ==> Parameters: 2(Integer), %li%(String)  
> Employee \[id=2, lastName=lisi, email=tang\_greatman@qq.com, gender=2\]  
> DEBUG - Resetting autocommit to true on JDBC Connection \[com.mysql.jdbc.JDBC4Connection@58c1670b\]  
> DEBUG - Closing JDBC Connection \[com.mysql.jdbc.JDBC4Connection@58c1670b\]  
> DEBUG - Returned connection 1489069835 to pool.

由结果可以看到表名mybatis\_employee拼接成功。