Jdbc和Mybatis的增删改查

背景

在实习期间，结合公司的开发体系架构，在导入公司的综合配置文件依赖之后，在基础上进行Jdbc和Myabtis增删改查的联系。

开发前提

建立一个标准的 maven 的项目，SDK改为自己本地jdk8位置，修改自己本地的 maven 环境以及仓库引入 springboot 的父依赖项目。导入公司自己封装的依赖包的依赖名称。建立符合要求的包机制，其中主启动类放置的位置需要和依赖自定义扫描的位置一致，否则需要自定义包扫描机制

@ComponentScan(value = "com.mao")

配置 maven 资源导出问题

    <build>
        <resources>
            <resource>
                <directory>src/main/resourcesdirectory>
                <excludes>
                    <exclude>**/*.propertiesexclude>
                    <exclude>**/*.xmlexclude>
                excludes>
                <filtering>falsefiltering>
            resource>
            <resource>
                <directory>src/main/javadirectory>
                <includes>
                    <include>**/*.propertiesinclude>
                    <include>**/*.xmlinclude>
                includes>
                <filtering>falsefiltering>
            resource>
        resources>
    build>

mybatis-config.xml 的配置文件

DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <settings>
        
        <setting name="cacheEnabled" value="true"/>
        
        <setting name="lazyLoadingEnabled" value="false"/>
        
        <setting name="aggressiveLazyLoading" value="false"/>
        
        <setting name="multipleResultSetsEnabled" value="true"/>
        
        <setting name="useColumnLabel" value="true"/>
        
        <setting name="useGeneratedKeys" value="true"/>
        
        <setting name="autoMappingBehavior" value="PARTIAL"/>
        
        <setting name="defaultExecutorType" value="SIMPLE"/>
        
        <setting name="defaultStatementTimeout" value="25000"/>

        
    settings>

configuration>

Jdbc

Jdbc 英文全称Java Database connect，翻译之后就是Java数据库连接。

基本的 Jdbc 查询流程

//下面方法有不同的异常，我直接抛出一个大的异常
public static void main(String[] args) throws Exception {   
        //1、导入 mysql 5 的驱动jar包
        //2、注册驱动
        Class.forName("com.mysql.jdbc.Driver");

        //3、获取数据库的连接对象
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/ems", "root", "123456");

        //4、定义sql语句
        String sql = "select * from studnet;";

        //5、获取执行sql语句的对象
        Statement stat = con.createStatement();

		//5、执行sql并接收返回结果
        ResultSet rs = stat.executeQuery(sql);

        //6、处理结果
       while (rs.next()){  //循环一次，游标移动一行
       		System.out.println("id：" + rs.getString(1)); //  获取第一列的数据
       		//获取字段为name的数据
            System.out.println("name：" + rs.getString("name"));  
            System.out.println("age：" + rs.getInt(3)); //  获取第三列的数据
            System.out.println("score：" + rs.getInt(4)); //  获取第四列的数据
       }
        //8、释放资源
        rs.close();
        stat.close();
        con.close();
    }

建立StudentJdbc 类，组件化方面进行 Jdbc 的增删改查，其中引用到公司的jar包依赖，可能会发生数据源的冲突，如下

org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'studentController': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: 
Error creating bean with name 'studentJdbc': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'javax.sql.DataSource' available: expected single matching bean but found 2: maoDatasource,hisDatasource

就是不清楚的数据源来源，发生了数据源冲突，注入数据源的时候需要通过 name 属性指定数据源

@Component
public class StudentJdbc {

    @Resource(name = "maoDatasource")
    private DataSource dataSource;
    
}

查询全部数据的业务函数，由于在自定义的配置文件中已经连接到本地的数据库了，所以在构造连接的时候采用的是无参构造函数生成 statement，在最开始生成变量值为null，在使用的时候进行new的初始化，查询的时候需要增加一个结果集资源，在结束的时候需要逆向关闭三个连接资源。

public List<Student> jdbcList() throws SQLException {
        List<Student> list = new ArrayList<>();
        Connection conn = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            conn = dataSource.getConnection();
            // 链接创建 Statement
            statement = conn.createStatement();
            resultSet = statement.executeQuery("select * from student where deleted = 0");
            // 遍历结果集
            while (resultSet.next()) {
                int id = resultSet.getInt("id");
                String username = resultSet.getString("username");
                String password = resultSet.getString("password");
                int deleted = resultSet.getInt("deleted");
                Student student = new Student(id, username, password,deleted);
                list.add(student);
                System.out.println("id：" + resultSet.getInt("id") + "用户名：" + resultSet.getString("username") + "密码" + resultSet.getString("password"));
            }
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            resultSet.close();
            statement.close();
            conn.close();
        }
        return list;
    }

增加函数的代码，使用了预编译 Statement，防止 SQL 的注入风险，sql 字符串使用占位符 ? ，预编译sql，通过 prepareStatement 放置对象，占位符标识从 1 开始，最终更新执行，结果返回一个 int 型的变量。

public int jdbcAdd(Student student) throws SQLException {
        Connection conn = null;
        PreparedStatement preStatement = null;
        try {
            conn = dataSource.getConnection();
            String sql = "insert into student(id,username,password) values (?,?,?);";
            preStatement = conn.prepareStatement(sql);
            preStatement.setInt(1,student.getId());
            preStatement.setString(2,student.getUsername());
            preStatement.setString(3,student.getPassword());
            return preStatement.executeUpdate();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            preStatement.close();
            conn.close();
        }
    }

修改代码实现

public int jdbcUpdate(Student student) throws SQLException {
        Connection conn = null;
        PreparedStatement preStatement = null;
        try {
            conn = dataSource.getConnection();
            String sql = "update student set username = ?,password = ? where id = ?;";
            preStatement = conn.prepareStatement(sql);
            preStatement.setString(1,student.getUsername());
            preStatement.setString(2,student.getPassword());
            preStatement.setInt(3,student.getId());

            return preStatement.executeUpdate();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            conn.close();
            preStatement.close();
        }
    }

删除代码实现

public int jdbcRemove(Integer id) throws SQLException {
        Connection conn = null;
        PreparedStatement preStatement = null;
        try {
            conn = dataSource.getConnection();
            String sql = "update student set deleted = 1 where id = ?;";
            preStatement = conn.prepareStatement(sql);
            preStatement.setInt(1,id);
            return preStatement.executeUpdate();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            preStatement.close();
            conn.close();
        }
    }

Mybatis

Mybatis 官方文档

定义的 mapper接口

public interface StudentMapper {

    List<Student> list(String username);

    int add(Student student);

    int update(Student student);

    int remove(Integer id);

}

对应 mapper.xml 配置文件 SQL 语句的编写

DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.sunri.mapper.StudentMapper">

    <insert id="add" parameterType="com.sunri.entity.Student">
        insert into student(id,username,password) values (#{id},#{username},#{password});
    insert>

    <update id="update">
        update student
        <set>
            <if test="username != null">username=#{username},if>
            <if test="password != null">password=#{password},if>
        set>
        where id = #{id} and deleted = 0;
    update>

    <update id="remove">
        update student set deleted = 1 where id = #{id} and deleted = 0;
    update>

    <select id="list" resultType="com.sunri.entity.Student">
        select * from student
        <where>
            <if test="username!=null and username!=''">
                username like '%${username}%'
            if>
            and deleted = 0
        where>
    select>

mapper>

测试出现的问题

类似于这种点击发送即可