MyBatis模拟实现

本章我们将可以自己编写代码，模拟MyBatis的简单实现

先回顾MyBatis的实现过程：

1）通过SQLSessionFactoryBuilder创建SQLSessionFactory时，将核心配置文件中configuration节点的内容，解析到SQLSessionFactory中

2）通过SQLSessionFactory获得SqlSession时，返回DefaultSqlSession

3）调用SQLSessionFactory的getMapper方法时，返回了DAO接口的代理对象，代理对象在invoke方法中实现了增删改查操作

4）具体的增删改查操作通过JDBC+SQL实现

下面我们模拟实现上面的过程：

1、模拟配置文件mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>

<configuration>

<environments default="develop">

<environment id="develop">

<transactionManager type="JDBC"></transactionManager>

<dataSource type="POOLED">

<property name="driver" value="com.mysql.jdbc.Driver"/>

<property name="url" value="jdbc:mysql://localhost:3306/test_db"/>

<property name="username" value="root"/>

<property name="password" value="123456"/>

</dataSource>

</environment>

</environments>

<mappers>

<!--<package name="com.qf.mbs.mapper"/>-->

<mapper resource="com/qf/mbs/mapper/UserDAO.xml"/>

<mapper class="com.qf.mbs.dao.UserDAO"/>

</mappers>

</configuration>

DAO接口：

public interface UserDAO {

List<User> findAll();

User findById(Integer id);

void addUser(User user);

void updateUser(User user);

void deleteUser(Integer id);

}

Mapper文件：

<?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.qf.mbs.dao.UserDAO">

<insert id="addUser" parameterType="com.qf.mbs.po.User">

<selectKey keyProperty="id" resultType="int" order="AFTER">

SELECT LAST_INSERT_ID()

</selectKey>

INSERT INTO USER (USERNAME,BIRTHDAY,SEX,ADDRESS) VALUES (#{username},#{birthday},#{sex},#{address})

</insert>

<update id="updateUser" parameterType="com.qf.mbs.po.User">

UPDATE USER set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} where id=#{id}

</update>

<delete id="deleteUser" parameterType="java.lang.Integer">

DELETE FROM USER where id=#{id}

</delete>

<select id="findById" parameterType="java.lang.Integer" resultType="com.qf.mbs.po.User">

SELECT * FROM USER where id=#{id}

</select>

<select id="findAll" resultType="com.qf.mbs.po.User">

select * from user

</select>

</mapper>

/**

配置文件的解析类

*/

public class ConfigParser {

//保存数据源信息

private Map<String,String> dataSource = new HashMap<>();

//保存映射文件路径

private List<String> resourceMappers = new ArrayList<>();

//保存class映射类名

private List<String> classMappers = new ArrayList<>();

public void parseConfig(InputStream inputStream) throws DocumentException {

SAXReader reader = new SAXReader();

reader.setEntityResolver(new EntityResolver() {

@Override

public InputSource resolveEntity(String publicId, String systemId) throws SAXException, IOException {

return new InputSource(new ByteArrayInputStream("".getBytes()));

}

});

Document doc = reader.read(inputStream);

Element rootElement = doc.getRootElement();

List<Element> properties = rootElement.element("environments").element("environment").element("dataSource").elements();

for(Element property : properties){

if("driver".equals(property.attributeValue("name"))){

dataSource.put("driver",property.attributeValue("value"));

}

if("url".equals(property.attributeValue("name"))){

dataSource.put("url",property.attributeValue("value"));

}

if("username".equals(property.attributeValue("name"))){

dataSource.put("username",property.attributeValue("value"));

}

if("password".equals(property.attributeValue("name"))){

dataSource.put("password",property.attributeValue("value"));

}

}

List<Element> mapperEles = rootElement.element("mappers").elements();

for(Element mapper : mapperEles){

if(mapper.attribute("resource") != null){

resourceMappers.add(mapper.attributeValue("resource"));

}

if(mapper.attribute("class") != null){

classMappers.add(mapper.attributeValue("class"));

}

}

}

public Map<String, String> getDataSource() {

return dataSource;

}

public List<String> getResourceMappers() {

return resourceMappers;

}

public List<String> getClassMappers() {

return classMappers;

}

}

测试：

@Test

public void testParse(){

ConfigParser parser = new ConfigParser();

try {

parser.parseConfig(Test2.class.getClassLoader().getResourceAsStream("mock-config.xml"));

System.out.println(parser.getDataSource());

System.out.println(parser.getClassMappers());

System.out.println(parser.getResourceMappers());

} catch (DocumentException e) {

e.printStackTrace();

}

}

/**

* SQL映射类

*/

public class Mapper {

//sql类型 insert update delete select

private String sqlType;

//Mapper方法名

private String methodName;

//sql语句

private String sql;

//参数类型

private String paramType;

//返回类型

private String returnType;

....

}

/**

映射文件的解析类

*/

public class MapperParser {

private Map<String,Mapper> mappers = new HashMap<>();

public void parseMappers(InputStream inputStream) throws DocumentException {

SAXReader reader = new SAXReader();

reader.setEntityResolver(new EntityResolver() {

@Override

public InputSource resolveEntity(String publicId, String systemId) throws SAXException, IOException {

return new InputSource(new ByteArrayInputStream("".getBytes()));

}

});

Document doc = reader.read(inputStream);

Element root = doc.getRootElement();

List<Element> elements = root.elements();

String namespace = root.attributeValue("namespace");

for(Element e : elements){

Mapper mapper = new Mapper();

mapper.setSqlType(e.getName());

mapper.setMethodName(e.attributeValue("id"));

mapper.setParamType(e.attributeValue("parameterType"));

mapper.setReturnType(e.attributeValue("resultType"));

mapper.setSql(e.getText());

mappers.put(namespace+"."+e.attributeValue("id"),mapper);

}

}

public Map<String, Mapper> getMappers() {

return mappers;

}

}

测试：

@Test

public void testParse(){

ConfigParser parser = new ConfigParser();

MapperParser mParser = new MapperParser();

try {

parser.parseConfig(Test2.class.getClassLoader().getResourceAsStream("mock-config.xml"));

System.out.println(parser.getDataSource());

System.out.println(parser.getClassMappers());

System.out.println(parser.getResourceMappers());

for(String resource : parser.getResourceMappers()){

System.out.println("resourc:"+resource);

mParser.parseMappers(Test2.class.getClassLoader().getResourceAsStream(resource));

System.out.println(mParser.getMappers());

}

} catch (DocumentException e) {

e.printStackTrace();

}

}

/**

* 模拟SqlSession

*/

public interface MySqlSession {

/**

* 返回Mapper对象

* @param clazz

* @param <T>

* @return

*/

<T> T getMapper(Class<T> clazz);

}

public class MySqlSessionImpl implements MySqlSession {

private Map<String,String> dataSource;

private Map<String,Mapper> mappers;

public MySqlSessionImpl(Map<String, String> dataSource, Map<String, Mapper> mappers) {

this.dataSource = dataSource;

this.mappers = mappers;

}

@Override

public <T> T getMapper(Class<T> clazz) {

XMLMapperProxy xmlMapperProxy = new XMLMapperProxy(dataSource,mappers,clazz);

return (T) xmlMapperProxy.getProxy();

}

}

/**

* XML映射文件的代理

*/

public class XMLMapperProxy implements InvocationHandler{

private Map<String,String> dataSource;

private Map<String,Mapper> mappers;

private Class<?> clazz;

private Connection connection;

public XMLMapperProxy(Map<String, String> dataSource, Map<String,Mapper> mappers,Class clazz) {

this.dataSource = dataSource;

this.mappers = mappers;

this.clazz = clazz;

initDatasource(dataSource);

}

/**

* 获得代理对象

* @return

*/

public Object getProxy(){

return Proxy.newProxyInstance(this.getClass().getClassLoader(),new Class[]{clazz},this);

}

@Override

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

String key = clazz.getName() + "." + method.getName();

Mapper mapper = mappers.get(key);

System.out.println("mapper--->"+mapper);

if(mapper == null){

System.out.println(key+",has no mapper.");

return null;

}

PreparedStatement psmt = connection.prepareStatement(mapper.getSql());

Object result = null;

if("select".equals(mapper.getSqlType())){

ResultSet rs = psmt.executeQuery();

List<String> columns = new ArrayList<>();

int count = rs.getMetaData().getColumnCount();

for(int i = 1;i <= count;i++){

columns.add(rs.getMetaData().getColumnName(i));

}

List selectRs = new ArrayList();

while(rs.next()){

Class<?> poClazz = Class.forName(mapper.getReturnType());

Object po = poClazz.newInstance();

for(String colName : columns){

for(Method med : poClazz.getMethods()){

if(med.getName().equalsIgnoreCase("set"+colName)){

try{

med.invoke(po,rs.getString(colName));

}catch (IllegalArgumentException ex) {

med.invoke(po, rs.getInt(colName));

}

}

}

}

selectRs.add(po);

}

result = selectRs;

}else{

result = psmt.executeUpdate();

}

connection.close();

return result;

}

private void initDatasource(Map<String,String> dataSource){

try {

Class.forName(dataSource.get("driver"));

connection = DriverManager.getConnection(dataSource.get("url"),dataSource.get("username"),dataSource.get("password"));

} catch (ClassNotFoundException e) {

e.printStackTrace();

} catch (SQLException e) {

e.printStackTrace();

}

}

}

工厂：

public class MySqlSessionFactory {

private String config;

public MySqlSessionFactory(String config) {

this.config = config;

}

public MySqlSession openSession(){

ConfigParser parser = new ConfigParser();

MapperParser mParser = new MapperParser();

try {

parser.parseConfig(MySqlSessionFactory.class.getClassLoader().getResourceAsStream(config));

System.out.println(parser.getDataSource());

System.out.println(parser.getClassMappers());

System.out.println(parser.getResourceMappers());

for(String resource : parser.getResourceMappers()){

System.out.println("resource:"+resource);

mParser.parseMappers(MySqlSessionFactory.class.getClassLoader().getResourceAsStream(resource));

System.out.println(mParser.getMappers());

}

return new MySqlSessionImpl(parser.getDataSource(),mParser.getMappers());

} catch (DocumentException e) {

e.printStackTrace();

}

return null;

}

}

工厂的创建器

public class MySqlSessionFactoryBuilder {

public MySqlSessionFactory build(String config){

return new MySqlSessionFactory(config);

}

}

测试：

@Test

public void testSelect(){

MySqlSessionFactory factory = new MySqlSessionFactoryBuilder().build("mock-config.xml");

MySqlSession mySqlSession = factory.openSession();

UserDAO mapper = mySqlSession.getMapper(UserDAO.class);

List<User> user = mapper.findAll();

System.out.println("user--->"+user);

}

到此我们按照MyBatis的源码，简单模拟了它的实现过程，这样我们会MyBatis这个框架会有更深入的理解。