用JavaSE简单入门MyBatis连接MySQL…

在Netbeans中新建一个 Java——Java应用程序项目，其目录结构如下：

需要准备和下载的jar库：1、mybatis-3.4.1.jar2、mysql-connector-java-5.1.39-bin.jar（安装MySQL的时候，勾选安装Connector.J后会附带有，在MySQL 安装目录/Connector.J 5.1 里面）
添加好库后，就可以开始干活了。首先得在MySQL里面建立数据库和表格：文件student.sql——不过这个文件并不参与MyBatis。我单独登录MySQLClient然后在命令行输入SQL语句创建的表格

CREATE DATABASESTUDENT_MANAGER;USESTUDENT_MANAGER;
CREATE TABLESTUDENT_TBL(STUDENT_ID VARCHAR(255) PRIMARYKEY,STUDENT_NAME VARCHAR(10) NOTNULL,STUDENT_SEX VARCHAR(10),STUDENT_BIRTHDAY DATE,CLASS_ID VARCHAR(255));
INSERT INTO STUDENT_TBL(STUDENT_ID, STUDENT_NAME, STUDENT_SEX, STUDENT_BIRTHDAY, CLASS_ID) VALUES (123456, '某某某', '女', '1980-08-01', 121546 )

创建完后数据库里面的内容，用MySQL Workbench查看：

然后我们开始编写类：首先，我们把这个STUDENT_TBL表的表头编写成一个POJO类（只含有成员变量，setter和getter的简单Java对象“PlainOrdinary Java Object”）文件StudentEntity.Java

packagemybatishelloworld;importjava.io.Serializable;importjava.util.Date;public class StudentEntityimplements Serializable {private static final longserialVersionUID = 3096154202413606831L;private DatestudentBirthday;private StringstudentID;private StringstudentName;private StringstudentSex;public DategetStudentBirthday() {returnstudentBirthday;}public String getStudentID(){return studentID;}public String getStudentName(){returnstudentName;}public String getStudentSex(){return studentSex;} // Setter…… …… …… ……public voidsetStudentBirthday(Date studentBirthday) {this.studentBirthday =studentBirthday;}public void setStudentID(StringstudentID) {this.studentID =studentID;}public voidsetStudentName(String studentName) {this.studentName =studentName;}public voidsetStudentSex(String studentSex) {this.studentSex =studentSex;} public void println(){ System.out.print(this.studentID+" "); System.out.print(this.studentName+" "); System.out.print(this.studentSex+" "); System.out.println(this.studentBirthday); }}

其实为了方便演示，这个Java类并不纯粹，而是添加了个println方法便于打印SQL后的结果
接着我们建立一个Mapper接口——于是，我们为什么需要一个映射（Mapper）接口呢？原因我们看看代码就懂了：文件StudentMapper.java

package mybatishelloworld;
import java.util.List;
public interface StudentMapper {public StudentEntitygetStudent(String studentID);public StudentEntitygetStudentAndClass(String studentID);public List getStudentAll();
public voidinsertStudent(StudentEntity entity);public voiddeleteStudent(StudentEntity entity);public voidupdateStudent(StudentEntity entity);}

我们发现，这个接口里面都是方法名。按照常规的Java思维，要真正用接口，必须有方法的实现才行：public class StudentMapperImplimplements StudentMapper{ @Override public StudentEntity getStudent(StringstudentID) {StudentEntityse=SQL.get(studentID); //那个头疼啊，还像JDBC一样把SQL语句写到字符串里面？ } ……………………}但是！但是的但是！这个具体的实现，在Mybatis里面，不需要我们写Java了。你可以把怎么用SQL语句get这个StudentEntity，写到一个xml文件里面。所以，这个接口Interface，就是用来映射XML文件里面的SQL查询语句的，如何把xml里的sql转换为java语句里的jdbc，交由MyBatis来完成。下面就是与之相对应的XML文件：文件StudentMapper.xml

<?xmlversion="1.0"encoding="UTF-8"?><!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mappernamespace="mybatishelloworld.StudentMapper"> <resultMaptype="StudentEntity"id="studentResultMap"><idproperty="studentID"column="STUDENT_ID"/><resultproperty="studentName"column="STUDENT_NAME"/><resultproperty="studentSex"column="STUDENT_SEX"/><resultproperty="studentBirthday"column="STUDENT_BIRTHDAY"/></resultMap><selectid="getStudent"parameterType="String"resultType="StudentEntity"resultMap="studentResultMap"><![CDATA[SELECT * from STUDENT_TBLSTWHERE ST.STUDENT_ID =#{studentID}]]></select><selectid="getStudentAll"resultType="StudentEntity"resultMap="studentResultMap"><![CDATA[SELECT * fromSTUDENT_TBL]]></select></mapper>

为了使用Mybatis，我们还得个它一个配置文件，配置所使用的数据库类型，数据库连接地址，用户名和密码等等，这个文件的配置如下：文件mybatis-config.xml

<?xmlversion="1.0"encoding="UTF-8"?><!DOCTYPEconfiguration PUBLIC"-//mybatis.org//DTD Config3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration> <typeAliases> <typeAliasalias="StudentEntity"type="mybatishelloworld.StudentEntity"/></typeAliases> <environmentsdefault="development"> <environmentid="development"> <transactionManagertype="JDBC"/> <dataSourcetype="POOLED"> <propertyname="driver"value="com.mysql.jdbc.Driver"/> <propertyname="url"value="jdbc:mysql://localhost:3306/student_manager?useSSL=true"/> <propertyname="username"value="root"/> <propertyname="password"value="rootOfPasswd"/> </dataSource> </environment></environments> <mappers> <mapperresource="mybatishelloworld/StudentMapper.xml"/></mappers></configuration>

数据库驱动跟Hibernate里面一样，连接MySQL的话，用的是value=com.mysql.jdbc.Driver
最后我们在MainClass的main函数里面，测试我们的整个配置文件MainClass.java

packagemybatishelloworld;
importjava.io.IOException;importjava.io.InputStream;importjava.util.List;importjava.util.logging.Level;importjava.util.logging.Logger;importorg.apache.ibatis.io.Resources;importorg.apache.ibatis.session.SqlSession;importorg.apache.ibatis.session.SqlSessionFactory;importorg.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MainClass{ public static void main(String[] args){ Stringresource = "mybatishelloworld/mybatis-config.xml"; //告诉MyBatis核心配置文件在哪里 InputStream inputStream = null; try{ inputStream =Resources.getResourceAsStream(resource); }catch(IOExceptionex){Logger.getLogger(MainClass.class.getName()).log(Level.SEVERE,null, ex);}
//打开SQL对话工厂 SqlSessionFactory sqlSessionFactory = newSqlSessionFactoryBuilder().build(inputStream); try(SqlSession session = sqlSessionFactory.openSession()) { //用工厂生成一个对话 //这里是精华，session用getMapper方法从xml里面生成了StudentMapper接口的实现类 StudentMapper mapper =(StudentMapper)session.getMapper(StudentMapper.class); StudentEntity se =mapper.getStudent("123456"); //于是这个类就有了具体的getStudent方法 se.println(); Listlist=mapper.getStudentAll(); list.forEach((s)->{ s.println(); }); } }//End-Of-Main}

在Netbeans编译运行后的结果：

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