深度自定义MyBatis

· 回顾mybatis的操作的核心步骤

· 编写核心类SqlSessionFacotryBuild进行解析配置文件

· 深度分析解析SqlSessionFacotryBuild干的核心工作

· 编写核心类SqlSessionFacotry

· 深度分析解析SqlSessionFacotry干的核心工作

· 编写核心类SqlSession

· 深度分析解析SqlSession干的核心工作

· 总结自定义mybatis用的技术点

一. 回顾mybatis的操作的核心步骤

声明一点我们本篇主要探讨的是mybatis的注解方式的操作, 完全从头开始都是小编从头开搞的, 如果与其他大神的代码思维有出入请多指教

我们首先需要准备mybatis的核心配置文件(当然导入相关的坐标这里不在啰嗦)

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--数据库连接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///db6?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>

    </environments>
    <mappers>
        <!-- 配置sql语句编写的位置 -->
        <package name="cn.itcast.mapper"/>
    </mappers>
</configuration>

准备好结果的实体类以及在mapper接口上编写需要执行的sql语句

public class User {
    private Integer uid;
    private String username;
    private String password;
    private String nickname;
}

package cn.itcast.mapper;

import cn.itcast.pojo.User;
import org.apache.ibatis.annotations.Select;
import java.util.List;

public interface UserMapper {
    @Select("select * from users")
    List<User> findAll();
}

使用mybatis的api来帮助我们完成sql语句的执行以及结果集的封装

//1.关联主配置文件
InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
//2.解析配置文件
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlSessionFactory = builder.build(in);
//3.创建会话对象
SqlSession sqlSession = sqlSessionFactory.openSession();
//4.可以采用接口代理的方式
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAll();
System.out.println(all);
//5.释放资源
sqlSession.close();

思考: mybatis大致是如何帮我们完成相关操作的 ?

我们通过Resources的getResourceAsStream告诉了mybatis我们编写的核心配置文件的位置, mybatis就可以找到我们数据库的连接信息, 也同时找到我们编写的sql语句的地方, 然后可以将其解析按照某种规则存放起来, 我们通过调用接口代理的方式执行方法时, 可以找到对应方法上的sql语句然后执行将结果封装返回给我们

二. 编写核心类SqlSessionFacotryBuild进行解析配置文件

那么我们废话不多说开始我们自定义mybatis的旅程,

1.首先我们需要用户编写配置文件, 然后通过我们自己的Resources来告诉我们配置文件所在位置

package com.itheima.ibatis.configuration;

import java.io.InputStream;

public class Resources {

    public static InputStream getResourceAsStream(String path) {
        return ClassLoader.getSystemClassLoader().getResourceAsStream(path);
    }
}

2. 然后需要定义SqlSessionFacotryBuild来对配置文件进行解析分发

package com.itheima.ibatis.configuration;

import com.itheima.ibatis.core.session.SqlSessionFactory;
import com.itheima.ibatis.core.session.impl.DefaultSqlSessionFactory;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.Node;
import org.dom4j.io.SAXReader;

import javax.sql.DataSource;
import java.io.File;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.util.List;
import java.util.Properties;

public class SqlSessionFactoryBuilder {
    private Configuration configuration = new Configuration();

    public SqlSessionFactory build(InputStream in) {
        SAXReader saxReader = new SAXReader();
        Document document = null;
        try {
            document = saxReader.read(in);
        } catch (DocumentException e) {
            e.printStackTrace();
        }
        Element rootElement = document.getRootElement();
        parseEnvironment(rootElement.element("environments"));
        parseMapper(rootElement.element("mappers"));
        return new DefaultSqlSessionFactory(configuration);
    }

    private void parseMapper(Element mapper) {
        String pack = mapper.element("package").attributeValue("name");

        String directory = pack.replace(".", "/");
        String path = ClassLoader.getSystemClassLoader().getResource("").getPath();
        File mapperDir = new File(path, directory);
        if (!mapperDir.exists()) {
            throw new RuntimeException("找不到mapper映射");
        }
        findMapper(mapperDir, pack);
        // System.out.println(configuration.getSql());

    }

    private void findMapper(File mapperDir, String base) {
        File[] files = mapperDir.listFiles();
        if (files != null) {
            for (File file : files) {
                if (file.isFile()) {
                    if (file.getName().endsWith(".class")) {
                        String name = file.getName();
                        name = name.substring(0, name.lastIndexOf("."));
                        String className = base + "." + name;
                        initMapper(className);
                    }
                } else {
                    findMapper(file, base + "." + file.getName());
                }
            }
        }
    }

    private void initMapper(String className) {
        try {
            Class<?> clazz = Class.forName(className);
            Method[] methods = clazz.getMethods();
            for (Method method : methods) {
                if(method.getAnnotations().length>0){
                    Mapper mapper = ParseMapper.parse(method);
                    this.configuration.getMappers().put(className + "." + method.getName(), mapper);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void parseEnvironment(Element environments) {
        String defEnv = environments.attributeValue("default");
        Node node = environments.selectSingleNode("//environment[@id='" + defEnv + "']");
        List<Element> list = node.selectNodes("//property");
        Properties properties = new Properties();
        for (Element element : list) {
            String name = element.attributeValue("name");
            String value = element.attributeValue("value");
            properties.put(name, value);
        }
        DataSource dataSource = new DefaultDataSource().getDataSource(properties);
        configuration.setDataSource(dataSource);
    }
}

三. 深度分析解析SqlSessionFacotryBuild干的核心工作

1. build(InputStream in) 方法做的工作

①借助Dom4j的来解析了xml文件, 将environments解析工作分发给了parseEnvironment(Element environments)

②将mappers的解析工作分发给了parseMapper(Element mapper)

2. parseEnvironment(Element environments)方法做的工作

①主要解析了连接数据库的参数们, 并且创建了数据库连接池

自定义连接池非本章节的重点,所以这里内部本质采用的Druid连接池来做了简化

package com.itheima.ibatis.configuration;

import com.alibaba.druid.pool.DruidDataSourceFactory;

import javax.sql.DataSource;
import java.util.Properties;

public class DefaultDataSource {
    
    public DataSource getDataSource(Properties properties) {
        try {
            return DruidDataSourceFactory.createDataSource(properties);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

②将解析好的连接池放入configuration对象中,mappers成员变量先别纠结下一章节会讲解

package com.itheima.ibatis.configuration;

import lombok.Data;

import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;

@Data
public class Configuration {
    private Map<String, Mapper> mappers = new HashMap<>();
    private DataSource dataSource;
}

详细图解如下图

3.parseMapper(Element mapper) 方法做的工作

①解析出用户配置的package找到sql语句所在接口的文件夹, 交给initMapper来处理

②递归找到这个包下所有的.class文件,并且获取到接口的全类名, 然后交给initMapper来处理

③initMapper通过反射获取类中的每一个方法,将方法交给一个专门解析方法上的注解的工具类ParseMapper的parse方法处理,处理完后将其放到configuration中的mappers的集合中

④ParseMapper的parse方法做的工作, 这是解析配置的核心地方

package com.itheima.ibatis.configuration;

import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class ParseMapper {


    public static Mapper parse(Method method) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        Annotation[] annotations = method.getAnnotations();
        Object value = annotations[0].getClass().getMethod("value").invoke(annotations[0]);
        Mapper mapper = new Mapper();
        Class<?> resultType = method.getReturnType();
        String val = (String) value;
        Pattern pattern = Pattern.compile("\#\{\s*\w+\s*\}");
        Matcher matcher = pattern.matcher(val);
        List<String> paramNames = new ArrayList<>();
        while (matcher.find()) {
            String group = matcher.group();
            String fieldName = group.substring(2, group.length() - 1).trim();
            paramNames.add(fieldName);
        }
        String sql = val.replaceAll("\#\{\s*\w+\s*\}", "?");
        mapper.setSql(sql);
        mapper.setParameterNames(paramNames);
        mapper.setSql(sql);
        if (resultType == List.class) {
            mapper.setSelectList(true);
            Type genericReturnType = method.getGenericReturnType();
            ParameterizedType parameterizedType = (ParameterizedType) genericReturnType;
            Type actualTypeArgument = parameterizedType.getActualTypeArguments()[0];
            mapper.setResultType(actualTypeArgument.getTypeName());
            mapper.setType("SELECT");
        } else if (resultType == Integer.class || resultType == int.class) {
            mapper.setType("UPDATE");
        } else {
            mapper.setType("SELECT");
            mapper.setResultType(resultType.getName());
        }
        return mapper;
    }
}

首先拿到方法上的注解,得到用户填入的sql语句

然后处理sql语句#{参数}的这些数据, 然后将参数的顺序保存起来, 用来后期设置参数的数据做准备, 一个方法对应一个Mapper对象

然后再根据结果类型, 判断是什么类型相关的操作,方便后期执行对应的sql语句

四. 编写核心类SqlSessionFacotry

1.回顾那个地方创建的SqlSessionFacotry对象

经过SqlSessionFacotryBuilder的努力, 我们成功的将配置文件中核心的信息解析出来并放入了configuration对象中了, 然后我们此时将解析好的configuration传入到SqlSessionFacotry中

SqlSessionFactory的实现类如下:

public class DefaultSqlSessionFactory implements SqlSessionFactory {
    private final Configuration configuration;
    private TransactionManagement defaultTransactionManagement;

    public DefaultSqlSessionFactory(Configuration configuration) {
        this.configuration =configuration;
        defaultTransactionManagement = new DefaultTransactionManagement(configuration.getDataSource());
    }
    @Override
    public SqlSession openSession() {
        return new DefaultSqlSession(configuration,defaultTransactionManagement,false);
    }
}

2.添加事务管理器

事务管理是一个小的功能, 里面希望使用ThreadLocal集合来保证一个用户拿到的链接是同一个

事务管理的代码如下:

public class DefaultTransactionManagement implements TransactionManagement {
    private ThreadLocal<Connection> threadLocal = new ThreadLocal<>();
    private DataSource dataSource;

    public DefaultTransactionManagement(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    public Connection getConnection() {
        Connection connection = threadLocal.get();
        if (connection == null) {
            try {
                connection = dataSource.getConnection();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            threadLocal.set(connection);
        }
        return connection;
    }

    @Override
    public void commit() {
        Connection connection = threadLocal.get();
        if (connection != null ) {
            try {
                connection.commit();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }

    @Override
    public void rollback() {
        Connection connection = threadLocal.get();
        if (connection != null) {
            try {
                connection.rollback();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }


    public void close() {
        Connection connection = threadLocal.get();
        if (connection != null) {
            try {
                connection.close();
                threadLocal.remove();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public void begin() {
        Connection connection = threadLocal.get();
        if (connection != null) {
            try {
                connection.setAutoCommit(false);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

五. 深度分析解析SqlSessionFacotry干的核心工作

1. SqlSession openSession() 方法做的工作

可以看的出来我们在这个方法创建了DefaultSqlSession对象,并传入封装好的configuration,默认的事务管理器

默认通过openSession事务是开启的等等相关的参数

六.编写核心类SqlSession

其实有SqlSession的接口,我们使用的实现类是DefaultSession, 这里记录了解析的配置对象configuration

默认事务管理器对象transactionManagement, 默认事务开启的状态tx标记

package com.itheima.ibatis.core.session.impl;

import com.itheima.ibatis.configuration.Configuration;
import com.itheima.ibatis.configuration.Mapper;
import com.itheima.ibatis.core.BaseExecutor;
import com.itheima.ibatis.core.annotation.Param;
import com.itheima.ibatis.core.session.SqlSession;
import com.itheima.ibatis.core.transaction.TransactionManagement;
import java.lang.reflect.*;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class DefaultSqlSession implements SqlSession {
    private final Configuration configuration;
    private final boolean tx;
    private TransactionManagement transactionManagement;

    public DefaultSqlSession(Configuration configuration, TransactionManagement transactionManagement, boolean tx) {
        this.configuration = configuration;
        this.transactionManagement = transactionManagement;
        this.tx = tx;
    }
    public void close() {
        transactionManagement.close();
    }
    @Override
    public void commit() {
        transactionManagement.commit();
    }
    @Override
    public void rollback() {
        transactionManagement.rollback();
    }

    @Override
    public <T> List<T> selectList(String sqlId) {
        return selectList(sqlId, null);
    }

    @Override
    public <T> List<T> selectList(String sqlId, Object param) {
        List<Object> list = new BaseExecutor(transactionManagement, tx).queryList(getMapper(sqlId), param);
        return (List<T>) list;
    }

    @Override
    public <T> T selectOne(String sqlId) {
        return selectOne(sqlId, null);
    }

    @Override
    public <T> T selectOne(String sqlId, Object param) {
        return new BaseExecutor(transactionManagement, tx).query(getMapper(sqlId), param);
    }

    @Override
    public int delete(String sqlId) {
        return update0(sqlId, null);
    }

    @Override
    public int delete(String sqlId, Object param) {
        return update0(sqlId, param);
    }

    @Override
    public int update(String sqlId) {
        return update0(sqlId, null);
    }

    @Override
    public int update(String sqlId, Object param) {
        return update0(sqlId, param);
    }

    @Override
    public int insert(String sqlId) {
        return update0(sqlId, null);
    }

    @Override
    public int insert(String sqlId, Object param) {
        return update0(sqlId, param);
    }

    @Override
    public <T> T getMapper(Class<T> clazz) {
        Object o = Proxy.newProxyInstance(
                clazz.getClassLoader(),
                new Class[]{clazz}, new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        String sqlId = clazz.getName() + "." + method.getName();
                        Mapper mapper = configuration.getMappers().get(sqlId);
                        String type = mapper.getType();
                        Object findParam = null;
                        if (args != null) {
                            if (args.length == 1) {
                                Object param = args[0];
                                boolean isArray = param.getClass().isArray();
                                if (!isArray) {
                                    findParam = param;
                                }
                            } else {
                                Map<String, Object> map = new HashMap<>();
                                Parameter[] parameters = method.getParameters();
                                for (int i = 0; i < parameters.length; i++) {
                                    Param param = parameters[i].getAnnotation(Param.class);
                                    String key = "arg"+i;
                                    if(param !=null){
                                        key = param.value();
                                    }
                                    map.put(key, args[i]);
                                }
                                findParam = map;
                            }
                        }

                        if (type.equals("SELECT")) {
                            boolean selectList = mapper.isSelectList();
                            if (selectList)
                                return selectList(sqlId, findParam);
                            else
                                return selectOne(sqlId, findParam);
                        } else {
                            return update0(sqlId, findParam);
                        }
                    }
                });
        return (T) o;
    }

    private int update0(String sqlId, Object param) {
        return new BaseExecutor(transactionManagement, tx).update(getMapper(sqlId), param);
    }

    public Mapper getMapper(String sqlId) {
        Mapper mapper = configuration.getMappers().get(sqlId);
        if (mapper == null) {
            throw new RuntimeException("没有找到sql映射,请检查");
        }
        return mapper;
    }
}