自定义一个简单的MyBatis -- XML -- queryAll

为了使用起来和mybatis是一样一样的，名字也跟mybatis一样，先出一个xml版本的查询

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.bl</groupId>
  <artifactId>mybatis</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <dependencies>

    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.38</version>
    </dependency>

    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>

    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.13-beta-2</version>
    </dependency>

    <dependency>
      <groupId>dom4j</groupId>
      <artifactId>dom4j</artifactId>
      <version>1.6.1</version>
    </dependency>

    <dependency>
      <groupId>jaxen</groupId>
      <artifactId>jaxen</artifactId>
      <version>1.1.6</version>
    </dependency>
  </dependencies>

</project>

TestMybatis

package com.bl.myMyBatis.test;

import com.bl.domain.User;
import com.bl.myMyBatis.core.SqlSession;
import com.bl.myMyBatis.core.SqlSessionFactory;
import com.bl.myMyBatis.core.SqlSessionFactoryBuilder;
import com.bl.myMyBatis.io.Resources;
import org.junit.Test;

import java.io.InputStream;
import java.util.List;

/**
 * @Deacription 测试自定义的mybatis
 * @Author BarryLee
 * @Date 2019/11/10 22:36
 */
public class TestMybatis {
  @Test
  public void test() {
    InputStream in = Resources.getResourceAsStream("sqlMapConfig.xml");
    SqlSessionFactory factory = SqlSessionFactoryBuilder.build(in);
    SqlSession session = factory.openSession();
    IUserMapper mapper = session.getMapper(IUserMapper.class);
    List<User> users = mapper.queryAll();
    for(User user: users) {
      System.out.println(user);
    }
  }
}

sqlMapConfig.xml

<?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">

<!-- 这是MyBatis的主配置文件 -->

<configuration>
  <!-- 配置环境 -->
  <environments default="mysql">
    <!-- 配置mysql环境变量 -->
    <environment id="mysql">
      <!-- 事务类型 -->
      <transactionManager type="JDBC"></transactionManager>
      <!-- 数据源（连接池） -->
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/test"/>
        <property name="username" value="root"/>
        <property name="password" value="barry"/>
      </dataSource>
    </environment>
  </environments>

  <!--使用XML，这里应该是resource-->
  <mappers>
    <mapper resource="com/bl/dao/IUserMapper.xml"></mapper>
  </mappers>
</configuration>

IUserMapper.xml

<?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="com.bl.dao.IUserMapper">
  <select id="queryAll" resultType="com.bl.domain.User">
    select * from user
  </select>
</mapper>

Configuration

package com.bl.myMyBatis.config;

import java.util.HashMap;
import java.util.Map;

/**
 * @Deacription TODO
 * @Author BarryLee
 * @Date 2019/11/10 17:40
 */
public class Configuration {
  private String driver;
  private String url;
  private String username;
  private String password;
  private Map<String, Mapper> mappers = new HashMap<String, Mapper>();

  public Map<String, Mapper> getMappers() {
    return mappers;
  }

  public void setMappers(Map<String, Mapper> mappers) {
    this.mappers.putAll(mappers);
  }

  public String getDriver() {
    return driver;
  }

  public void setDriver(String driver) {
    this.driver = driver;
  }

  public String getUrl() {
    return url;
  }

  public void setUrl(String url) {
    this.url = url;
  }

  public String getUsername() {
    return username;
  }

  public void setUsername(String username) {
    this.username = username;
  }

  public String getPassword() {
    return password;
  }

  public void setPassword(String password) {
    this.password = password;
  }
}

Mapper

package com.bl.myMyBatis.config;

/**
 * @Deacription TODO
 * @Author BarryLee
 * @Date 2019/11/10 20:04
 */
public class Mapper {
  private String queryString; // sql
  private String resultType;

  public String getQueryString() {
    return queryString;
  }

  public void setQueryString(String queryString) {
    this.queryString = queryString;
  }

  public String getResultType() {
    return resultType;
  }

  public void setResultType(String resultType) {
    this.resultType = resultType;
  }
}

DataSourceUtil

package com.bl.myMyBatis.utils;

import com.bl.myMyBatis.config.Configuration;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

/**
 * @Deacription TODO
 * @Author BarryLee
 * @Date 2019/11/10 21:42
 */
public class DataSourceUtil {

  /**
   * 获取连接，这里没有使用单例
   * @param cfg
   * @return
   */
  public static Connection getConnection(Configuration cfg) {
    try {
      Class.forName(cfg.getDriver());
      return DriverManager.getConnection(cfg.getUrl(), cfg.getUsername(), cfg.getPassword());
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    } catch (SQLException e) {
      e.printStackTrace();
    }
    return null;
  }
}

Executor

package com.bl.myMyBatis.utils;

import com.bl.myMyBatis.config.Mapper;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;

/**
 * @Deacription 负责执行SQL语句，并且封装结果集
 * @Author BarryLee
 * @Date 2019/11/10 22:15
 */
public class Executor {

  public <E> List<E> selectList(Mapper mapper, Connection conn) {
    PreparedStatement pstm = null;
    ResultSet rs = null;
    try {
      //1.取出mapper中的数据
      String queryString = mapper.getQueryString();//select * from user
      String resultType = mapper.getResultType();//com.itheima.domain.User
      Class domainClass = Class.forName(resultType);
      //2.获取PreparedStatement对象
      pstm = conn.prepareStatement(queryString);
      //3.执行SQL语句，获取结果集
      rs = pstm.executeQuery();
      //4.封装结果集
      List<E> list = new ArrayList<E>();//定义返回值
      while(rs.next()) {
        //实例化要封装的实体类对象
        E obj = (E)domainClass.newInstance();

        //取出结果集的元信息：ResultSetMetaData
        ResultSetMetaData rsmd = rs.getMetaData();
        //取出总列数
        int columnCount = rsmd.getColumnCount();
        //遍历总列数
        for (int i = 1; i <= columnCount; i++) {
          //获取每列的名称，列名的序号是从1开始的
          String columnName = rsmd.getColumnName(i);
          //根据得到列名，获取每列的值
          Object columnValue = rs.getObject(columnName);
          //给obj赋值：使用Java内省机制（借助PropertyDescriptor实现属性的封装）
          PropertyDescriptor pd = new PropertyDescriptor(columnName,domainClass);//要求：实体类的属性和数据库表的列名保持一种
          //获取它的写入方法
          Method writeMethod = pd.getWriteMethod();
          //把获取的列的值，给对象赋值
          writeMethod.invoke(obj,columnValue);
        }
        //把赋好值的对象加入到集合中
        list.add(obj);
      }
      return list;
    } catch (Exception e) {
      throw new RuntimeException(e);
    } finally {
      release(pstm,rs);
    }
  }


  private void release(PreparedStatement pstm,ResultSet rs){
    if(rs != null){
      try {
        rs.close();
      }catch(Exception e){
        e.printStackTrace();
      }
    }

    if(pstm != null){
      try {
        pstm.close();
      }catch(Exception e){
        e.printStackTrace();
      }
    }
  }
}

XmlConfigBuilder

package com.bl.myMyBatis.utils;

import com.bl.myMyBatis.config.Configuration;
import com.bl.myMyBatis.config.Mapper;
import org.apache.ibatis.io.Resources;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 *  用于解析配置文件
 */
public class XMLConfigBuilder {

    /**
     * 解析主配置文件，把里面的内容填充到DefaultSqlSession所需要的地方
     * 使用的技术：
     *      dom4j+xpath
     */
    public static Configuration loadConfiguration(InputStream config){
        try{
            //定义封装连接信息的配置对象（mybatis的配置对象）
            Configuration cfg = new Configuration();

            //1.获取SAXReader对象
            SAXReader reader = new SAXReader();
            //2.根据字节输入流获取Document对象
            Document document = reader.read(config);
            //3.获取根节点
            Element root = document.getRootElement();
            //4.使用xpath中选择指定节点的方式，获取所有property节点
            List<Element> propertyElements = root.selectNodes("//property");
            //5.遍历节点
            for(Element propertyElement : propertyElements){
                //判断节点是连接数据库的哪部分信息
                //取出name属性的值
                String name = propertyElement.attributeValue("name");
                if("driver".equals(name)){
                    //表示驱动
                    //获取property标签value属性的值
                    String driver = propertyElement.attributeValue("value");
                    cfg.setDriver(driver);
                }
                if("url".equals(name)){
                    //表示连接字符串
                    //获取property标签value属性的值
                    String url = propertyElement.attributeValue("value");
                    cfg.setUrl(url);
                }
                if("username".equals(name)){
                    //表示用户名
                    //获取property标签value属性的值
                    String username = propertyElement.attributeValue("value");
                    cfg.setUsername(username);
                }
                if("password".equals(name)){
                    //表示密码
                    //获取property标签value属性的值
                    String password = propertyElement.attributeValue("value");
                    cfg.setPassword(password);
                }
            }
            //取出mappers中的所有mapper标签，判断他们使用了resource还是class属性
            List<Element> mapperElements = root.selectNodes("//mappers/mapper");
            //遍历集合
            for(Element mapperElement : mapperElements){
                //判断mapperElement使用的是哪个属性
                Attribute attribute = mapperElement.attribute("resource");
                if(attribute != null){
                    System.out.println("使用的是XML");
                    //表示有resource属性，用的是XML
                    //取出属性的值
                    String mapperPath = attribute.getValue();//获取属性的值"com/itheima/dao/IUserDao.xml"
                    //把映射配置文件的内容获取出来，封装成一个map
                    Map<String, Mapper> mappers = loadMapperConfiguration(mapperPath);
                    //给configuration中的mappers赋值
                    cfg.setMappers(mappers);
                }
                //else{
                //    System.out.println("使用的是注解");
                //    //表示没有resource属性，用的是注解
                //    //获取class属性的值
                //    String daoClassPath = mapperElement.attributeValue("class");
                //    //根据daoClassPath获取封装的必要信息
                //    Map<String,Mapper> mappers = loadMapperAnnotation(daoClassPath);
                //    //给configuration中的mappers赋值
                //    cfg.setMappers(mappers);
                //}
            }
            //返回Configuration
            return cfg;
        }catch(Exception e){
            throw new RuntimeException(e);
        }finally{
            try {
                config.close();
            }catch(Exception e){
                e.printStackTrace();
            }
        }

    }

    /**
     * 根据传入的参数，解析XML，并且封装到Map中
     * @param mapperPath    映射配置文件的位置
     * @return  map中包含了获取的唯一标识（key是由dao的全限定类名和方法名组成）
     *          以及执行所需的必要信息（value是一个Mapper对象，里面存放的是执行的SQL语句和要封装的实体类全限定类名）
     */
    private static Map<String,Mapper> loadMapperConfiguration(String mapperPath)throws IOException {
        InputStream in = null;
        try{
            //定义返回值对象
            Map<String,Mapper> mappers = new HashMap<String,Mapper>();
            //1.根据路径获取字节输入流
            in = Resources.getResourceAsStream(mapperPath);
            //2.根据字节输入流获取Document对象
            SAXReader reader = new SAXReader();
            Document document = reader.read(in);
            //3.获取根节点
            Element root = document.getRootElement();
            //4.获取根节点的namespace属性取值
            String namespace = root.attributeValue("namespace");//是组成map中key的部分
            //5.获取所有的select节点
            List<Element> selectElements = root.selectNodes("//select");
            //6.遍历select节点集合
            for(Element selectElement : selectElements){
                //取出id属性的值      组成map中key的部分
                String id = selectElement.attributeValue("id");
                //取出resultType属性的值  组成map中value的部分
                String resultType = selectElement.attributeValue("resultType");
                //取出文本内容            组成map中value的部分
                String queryString = selectElement.getText();
                //创建Key
                String key = namespace+"."+id;
                //创建Value
                Mapper mapper = new Mapper();
                mapper.setQueryString(queryString);
                mapper.setResultType(resultType);
                //把key和value存入mappers中
                mappers.put(key,mapper);
            }
            return mappers;
        }catch(Exception e){
            throw new RuntimeException(e);
        }finally{
            in.close();
        }
    }

    /**
     * 根据传入的参数，得到dao中所有被select注解标注的方法。
     * 根据方法名称和类名，以及方法上注解value属性的值，组成Mapper的必要信息
     * @param daoClassPath
     * @return

    private static Map<String,Mapper> loadMapperAnnotation(String daoClassPath)throws Exception{
        //定义返回值对象
        Map<String,Mapper> mappers = new HashMap<String, Mapper>();

        //1.得到dao接口的字节码对象
        Class daoClass = Class.forName(daoClassPath);
        //2.得到dao接口中的方法数组
        Method[] methods = daoClass.getMethods();
        //3.遍历Method数组
        for(Method method : methods){
            //取出每一个方法，判断是否有select注解
            boolean isAnnotated = method.isAnnotationPresent(Select.class);
            if(isAnnotated){
                //创建Mapper对象
                Mapper mapper = new Mapper();
                //取出注解的value属性值
                Select selectAnno = method.getAnnotation(Select.class);
                String queryString = selectAnno.value();
                mapper.setQueryString(queryString);
                //获取当前方法的返回值，还要求必须带有泛型信息
                Type type = method.getGenericReturnType();//List<User>
                //判断type是不是参数化的类型
                if(type instanceof ParameterizedType){
                    //强转
                    ParameterizedType ptype = (ParameterizedType)type;
                    //得到参数化类型中的实际类型参数
                    Type[] types = ptype.getActualTypeArguments();
                    //取出第一个
                    Class domainClass = (Class)types[0];
                    //获取domainClass的类名
                    String resultType = domainClass.getName();
                    //给Mapper赋值
                    mapper.setResultType(resultType);
                }
                //组装key的信息
                //获取方法的名称
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();
                String key = className+"."+methodName;
                //给map赋值
                mappers.put(key,mapper);
            }
        }
        return mappers;
    }
     */






}

SqlSession

package com.bl.myMyBatis.core;

/**
 * @Deacription TODO
 * @Author BarryLee
 * @Date 2019/11/10 16:51
 */
public interface SqlSession {
  /**
   * @param daoInterfaceClass
   * @param <T> dao 接口字节码
   * @return
   */
  <T> T getMapper(Class<T> daoInterfaceClass);
}

SqlSessionFactory

package com.bl.myMyBatis.core;

public interface SqlSessionFactory {
  SqlSession openSession();
}

SqlSessionFactoryBuilder

package com.bl.myMyBatis.core;

import com.bl.myMyBatis.config.Configuration;
import com.bl.myMyBatis.utils.XMLConfigBuilder;

import java.io.InputStream;

/**
 * @Deacription 构建者模式 - 创建一个工厂（这里简单实现，具体应该有待斟酌）
 * @Author BarryLee
 * @Date 2019/11/10 16:49
 */
public class SqlSessionFactoryBuilder {
  public static SqlSessionFactory build(InputStream in){
    Configuration cfg = XMLConfigBuilder.loadConfiguration(in);
    return new DefaultSqlSessionFactory(cfg);
  }
}

DefaultSqlSession

package com.bl.myMyBatis.core;

import com.bl.myMyBatis.config.Configuration;
import com.bl.myMyBatis.utils.DataSourceUtil;

import java.lang.reflect.Proxy;
import java.sql.Connection;

/**
 * @Deacription TODO
 * @Author BarryLee
 * @Date 2019/11/10 20:56
 */
public class DefaultSqlSession implements SqlSession {

  private Configuration cfg;
  private Connection conn;

  public DefaultSqlSession(Configuration cfg) {
    this.cfg = cfg;
    // 根据配置(driver,url,username,password,mappers)获取一个连接
    conn = DataSourceUtil.getConnection(cfg);
  }

  public <T> T getMapper(Class<T> daoInterfaceClass) {
    return (T) Proxy.newProxyInstance(
        daoInterfaceClass.getClassLoader(),
        new Class[]{daoInterfaceClass},
        new MapperProxy(cfg.getMappers(), conn)
    );
  }
}

package com.bl.myMyBatis.core;

import com.bl.myMyBatis.config.Configuration;

/**
 * @Deacription TODO
 * @Author BarryLee
 * @Date 2019/11/10 20:57
 */
public class DefaultSqlSessionFactory implements SqlSessionFactory {
  private Configuration cfg;
  public DefaultSqlSessionFactory(Configuration cfg) {
    this.cfg = cfg;
  }
  public SqlSession openSession() {
    return new DefaultSqlSession(cfg);
  }
}

MapperProxy

package com.bl.myMyBatis.core;

import com.bl.myMyBatis.config.Mapper;
import com.bl.myMyBatis.utils.Executor;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.util.Map;

/**
 * @Deacription TODO
 * @Author BarryLee
 * @Date 2019/11/10 21:58
 */
public class MapperProxy implements InvocationHandler {
  private Map<String, Mapper> mappers;
  private Connection conn;
  public MapperProxy(Map<String, Mapper> mappers, Connection conn) {
    this.mappers = mappers;
    this.conn = conn;
  }

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    String className = method.getDeclaringClass().getName();
    String methodName = method.getName();
    String key = className + "." + methodName;
    Mapper mapper = mappers.get(key);
    if(mapper == null) {
      throw new IllegalArgumentException("传参有误");
    }

    // 调用工具类执行查询所有
    return new Executor().selectList(mapper,conn);
  }
}

package com.bl.myMyBatis.io;

import java.io.InputStream;

public class Resources {
  /**
   * 获取inputStream
   * @param path
   * @return
   */
  public static InputStream getResourceAsStream(String path) {
    return Resources.class.getClassLoader().getResourceAsStream(path);
  }
}

<?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">

<!-- 这是MyBatis的主配置文件 -->

<configuration>
  <!-- 配置环境 -->
  <environments default="mysql">
    <!-- 配置mysql环境变量 -->
    <environment id="mysql">
      <!-- 事务类型 -->
      <transactionManager type="JDBC"></transactionManager>
      <!-- 数据源（连接池） -->
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/test"/>
        <property name="username" value="root"/>
        <property name="password" value="barry"/>
      </dataSource>
    </environment>
  </environments>

  <!--使用注解：这里应该是class-->
  <mappers>
    <mapper class="com.bl.annotation.IUserDao"></mapper>
  </mappers>
</configuration>