- 1. MyBatis框架概念
- 2. MyBatis框架原理分析
- 3. MyBatis框架实现验证
mybatis三种实现方式
mybatis提供的API：这种方式不常用，比较原始的方式。
通过配置xml方式：使用最多，功能相对比较完善。
注解方式：减少很多配置，但是功能相较于xml没那么完善。
本篇要做的就是对mybatis的简单实现，并不是重复造轮子，为了更深入的理解mybatis原理机制，从作者角度去思考，才能更深如体会其中的思想。声明一下，大佬勿喷，只是为了学习，这只是仿照mybatis的简单实现，并不是mybatis，mybatis源码日后具体分析。
2. MyBatis框架原理分析执行顺序，上个图，比较清晰。
- 创建maven工程
- 引入依赖，这里没有引用mybatis，需要手动自己实现，包括xml解析，封装jdbc，封装结果集等。
4.0.0 com.zrj.mybatis mybatis_design 1.0-SNAPSHOT jar log4j log4j 1.2.12 dom4j dom4j 1.6.1 mysql mysql-connector-java 5.1.6 jaxen jaxen 1.1.6 junit junit 4.13
- 创建各种接口实现类
package com.zrj.mybatis.cfg;
import java.util.Map;
public class Configuration {
private String username;
private String password;
private String url;
private String driver;
private Map mappers;
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;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getDriver() {
return driver;
}
public void setDriver(String driver) {
this.driver = driver;
}
public Map getMappers() {
return mappers;
}
public void setMappers(Map mappers) {
this.mappers = mappers;
}
}
package com.zrj.mybatis.cfg;
public class Mapper {
private String queryString;
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;
}
}
package com.zrj.mybatis.cfg;
import com.zrj.mybatis.utils.Executor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.util.Map;
public class MapperProxyFactory implements InvocationHandler {
private Map mappers;
private Connection conn;
public MapperProxyFactory(Map mappers, Connection conn) {
this.mappers = mappers;
this.conn = conn;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//1.取出方法名
String methodName = method.getName();
//2.取出方法所在类名
String className = method.getDeclaringClass().getName();
//3.拼接成 Key
String key = className + "." + methodName;
//4.使用 key 取出 mapper
Mapper mapper = mappers.get( key );
if (mapper == null) {
throw new IllegalArgumentException( "传入的参数有误，无法获取执行的必要条件" );
}
//5.创建 Executor 对象
Executor executor = new Executor();
return executor.selectList( mapper, conn );
}
}
package com.zrj.mybatis.annotations;
import java.lang.annotation.*;
@documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Repeatable(Select.List.class)
public @interface Select {
String value();
String databaseId() default "";
@documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@interface List {
Select[] value();
}
}
package com.zrj.mybatis.io;
import java.io.InputStream;
public class Resources {
public static InputStream getResourceAsStream(String xmlPath) {
return Resources.class.getClassLoader().getResourceAsStream( xmlPath );
}
}
package com.zrj.mybatis.utils;
import com.zrj.mybatis.cfg.Configuration;
import java.sql.Connection;
import java.sql.DriverManager;
public class DataSourceUtil {
public static Connection getConnection(Configuration cfg) {
try {
Class.forName( cfg.getDriver() );
Connection conn = DriverManager.getConnection( cfg.getUrl(), cfg.getUsername(), cfg.getPassword() );
return conn;
} catch (Exception e) {
throw new RuntimeException( e );
}
}
}
package com.zrj.mybatis.utils;
import com.zrj.mybatis.annotations.Select;
import com.zrj.mybatis.cfg.Configuration;
import com.zrj.mybatis.cfg.Mapper;
import com.zrj.mybatis.io.Resources;
import com.zrj.mybatis.sqlsession.DefaultSqlSession;
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.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class XMLConfigBuilder {
public static void loadConfiguration(DefaultSqlSession session, 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 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 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
//获取属性的值"com/itheima/dao/IUserDao.xml"
String mapperPath = attribute.getValue();
//把映射配置文件的内容获取出来，封装成一个map
Map 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 mappers = loadMapperAnnotation( daoClassPath );
//给configuration中的mappers赋值
cfg.setMappers( mappers );
}
}
//把配置对象传递给 DefaultSqlSession
session.setCfg( cfg );
} catch (Exception e) {
throw new RuntimeException( e );
} finally {
try {
config.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
private static Map loadMapperConfiguration(String mapperPath) throws IOException {
InputStream in = null;
try {
//定义返回值对象
Map mappers = new HashMap();
//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
//是组成map中key的部分
String namespace = root.attributevalue( "namespace" );
//5.获取所有的select节点
List 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();
}
}
private static Map loadMapperAnnotation(String daoClassPath) throws Exception {
//定义返回值对象
Map mappers = new HashMap();
//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
//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;
}
}
package com.zrj.mybatis.utils;
import com.zrj.mybatis.cfg.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;
public class Executor {
public List selectList(Mapper mapper, Connection conn) {
PreparedStatement pstm = null;
ResultSet rs = null;
try {
//1.取出 mapper 中的数据
//select * from user
String queryString = mapper.getQueryString();
String resultType = mapper.getResultType();
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
//定义返回值
List list = new ArrayList();
while (rs.next()) {
//实例化要封装的实体类对象
//User 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）
//要求：实体类的属性和数据库表的列名保持一种
PropertyDescriptor pd = new PropertyDescriptor( columnName, domainClass );
//获取它的写入方
Method writeMethod = pd.getWriteMethod();
// setUsername(String username);
//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();
}
}
}
}
package com.zrj.mybatis.sqlsession;
import java.io.InputStream;
public class SqlSessionFactoryBuilder {
public SqlSessionFactory build(InputStream in) {
DefaultSqlSessionFactory factory = new DefaultSqlSessionFactory();
//给 factory 中 config 赋值
factory.setConfig( in );
return factory;
}
}
package com.zrj.mybatis.sqlsession;
public interface SqlSessionFactory {
SqlSession openSession();
}
package com.zrj.mybatis.sqlsession;
import com.zrj.mybatis.utils.XMLConfigBuilder;
import java.io.InputStream;
public class DefaultSqlSessionFactory implements SqlSessionFactory {
private InputStream config = null;
public void setConfig(InputStream config) {
this.config = config;
}
@Override
public SqlSession openSession() {
DefaultSqlSession session = new DefaultSqlSession();
//调用工具类解析 xml 文件
XMLConfigBuilder.loadConfiguration( session, config );
return session;
}
}
package com.zrj.mybatis.sqlsession;
public interface SqlSession {
T getMapper(Class daoClass);
void close();
}
package com.zrj.mybatis.sqlsession;
import com.zrj.mybatis.cfg.Configuration;
import com.zrj.mybatis.cfg.Mapper;
import com.zrj.mybatis.cfg.MapperProxyFactory;
import com.zrj.mybatis.utils.DataSourceUtil;
import com.zrj.mybatis.utils.Executor;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;
public class DefaultSqlSession implements SqlSession {
private Configuration cfg;
public void setCfg(Configuration cfg) {
this.cfg = cfg;
}
private Connection conn;
public Connection getConn() {
try {
conn = DataSourceUtil.getConnection( cfg );
return conn;
} catch (Exception e) {
throw new RuntimeException( e );
}
}
@Override
public T getMapper(Class daoClass) {
conn = getConn();
System.out.println( conn );
T daoProxy = (T) Proxy.newProxyInstance(
daoClass.getClassLoader(),
new Class[]{daoClass},
new MapperProxyFactory( cfg.getMappers(), conn )
);
return daoProxy;
}
@Override
public void close() {
try {
System.out.println( conn );
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
//查询所有方法
public List selectList(String statement) {
Mapper mapper = cfg.getMappers().get( statement );
return new Executor().selectList( mapper, conn );
}
}
# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, ConSOLE debug info warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE
# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, ConSOLE
# ConSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.ConSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %mn
# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=d:/axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %mn
User及UserDao，Book及BookDao参照上期不变，包括数据库表结构都与上期相同，类太多了就不重复列举了。
对象及dao接口参照地址
测试类只是调整了引用包路径，原来引用的是mybatis下，现在是自定义。
package com.mybatis.test;
import com.zrj.dao.BookDao;
import com.zrj.dao.UserDao;
import com.zrj.domain.Book;
import com.zrj.domain.User;
import com.zrj.mybatis.io.Resources;
import com.zrj.mybatis.sqlsession.SqlSession;
import com.zrj.mybatis.sqlsession.SqlSessionFactory;
import com.zrj.mybatis.sqlsession.SqlSessionFactoryBuilder;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class MyBatisTest {
@Test
public void myBatisTest() throws IOException {
// 1.读取配置文件
InputStream in = Resources.getResourceAsStream( "SqlMapConfig.xml" );
// 2.创建SqlSessionFactory工厂，初始化xml配置文件，转换为Configuration对象
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build( in );
// 3.使用工厂生产SQLSession对象，创建连接，事务等
SqlSession session = factory.openSession();
// 4.使用SQLSession创建Dao接口的代理对象，通过反射获取都太代理对象
UserDao userDao = session.getMapper( UserDao.class );
// 5.使用代理对象执行方法，执行动态sql，封装结果集ResultSet
List userList = userDao.findAll();
System.out.println( "-----------mybatis查询---------" );
userList.forEach( System.out::println );
// 6.释放资源
session.close();
in.close();
}
@Test
public void myBatisAnnoTest() throws IOException {
// 1.读取配置文件
InputStream in = Resources.getResourceAsStream( "SqlMapConfig.xml" );
// 2.创建SqlSessionFactory工厂
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build( in );
// 3.使用工厂生产SQLSession对象
SqlSession session = factory.openSession();
// 4.使用SQLSession创建Dao接口的代理对象
BookDao bookDao = session.getMapper( BookDao.class );
// 5.使用代理对象执行方法
List bookList = bookDao.findAll();
System.out.println( "-----------mybatis查询---------" );
bookList.forEach( System.out::println );
// 6.释放资源
session.close();
in.close();
}
}
