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模拟Mybatis的实现方法
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项目管理工具 : Maven
测试运行工具 : Junit
数据库 : Derby
XML操作工具:Dom4j
继续不废话
Maven Dependencies:
junit junit 4.9 test org.apache.derby derby 10.10.2.0 org.apache.derby derbyclient 10.10.2.0 dom4j dom4j 1.6.1
SQL 建表及数据插入（如果在第一节中作过，可以跳过此步）:
CREATE TABLE USER_TEST_TB( ID INT PRIMARY KEY, USERNAME VARCHAR(20) NOT NULL, PASSWORD VARCHAR(20) NOT NULL, NICKNAME VARCHAR(20) NOT NULL ); INSERT INTO USER_TEST_TB VALUES(1,'1st','111','Jack'); INSERT INTO USER_TEST_TB VALUES(2,'2nd','222','Rose'); INSERT INTO USER_TEST_TB VALUES(3,'3rd','333','Will');
Mybatis配置文件 src/main/resource源目录下
test-mybatis-configuration.xml <?xml version="1.0" encoding="UTF-8" ?>
User.java对象类(src/main/java/com/bjpowernode/practice目录下)
package com.bjpowernode.practice;
/**
*
* User Model
*
*/
public class User
{
private String id;
private String username;
private String password;
private String nickname;
public String getId()
{
return id;
}
public void setId(String id)
{
this.id = id;
}
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 getNickname()
{
return nickname;
}
public void setNickname(String nickname)
{
this.nickname = nickname;
}
} Select.java 注解类（src/main/java/com/bjpowernode/practice/annotation目录下）
package com.bjpowernode.practice.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/** 标注此注解只能用在方法上 */
@Target(ElementType.METHOD)
/** 标注此注解生命周期是在Runtime运行时 */
@Retention(RetentionPolicy.RUNTIME)
public @interface Select
{
String value();
} UserMapper.java 基于Annotation的配置类（src/main/java/com/bjpowernode/practice/annotation目录下）
package com.bjpowernode.practice.annotation;
import com.bjpowernode.practice.User;
import java.util.List;
public interface UserMapper
{
@Select("select * from USER_TEST_TB")
public List getUser();
} Mapper.java 对象类（src/main/java/com/bjpowernode/practice/simulation目录下）
package com.bjpowernode.practice.simulation;
/**
*
* 存储查询结果对象
*
*/
public class Mapper
{
/**
* 返回类型
*/
private String resultType;
/**
* 查询ＳＱＬ
*/
private String querySql;
public String getResultType()
{
return resultType;
}
public void setResultType(String resultType)
{
this.resultType = resultType;
}
public String getQuerySql()
{
return querySql;
}
public void setQuerySql(String querySql)
{
this.querySql = querySql;
}
} SQLSelectProxy.java AOP动态代理类（src/main/java/com/bjpowernode/practice/simulation目录下）
package com.bjpowernode.practice.simulation;
import com.bjpowernode.practice.annotation.Select;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.List;
public class SQLSelectProxy implements InvocationHandler
{
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
{
/**
* 获得Mapper方法上的Select注解,以此来取得注解中的SQL语句
*/
Select select = method.getAnnotation(Select.class);
if (!method.isAnnotationPresent(Select.class))
{
throw new RuntimeException("缺少@Select注解!");
}
PreparedStatement pstmt = null;
ResultSet rs = null;
Object obj = null;
try
{
pstmt = SqlSessionImpl.connection.prepareStatement(select.value());
rs = pstmt.executeQuery();
/**
* 获得Method的返回对象类型,此处应当作判断处理,当List的时候,当只返回一个对象的时候.
* 为了简单实现功能并与第一节中测试文件不发生冲突起见,此处当作List处理
*/
String returnType = method.getGenericReturnType().toString();//java.util.List
if (returnType.startsWith(List.class.getName()))
{
//去掉我们不需要的字符串，得到List中的类型
returnType = returnType.replace(List.class.getName(), "").replace("<", "").replace(">", "");
}
else
{
// 返回其他对象应当作其他处理，此处为了简单起见，暂不处理
}
obj = SqlSessionImpl.executeQuery(rs, returnType);
}
finally
{
if (rs != null && !rs.isClosed())
{
rs.close();
}
if (pstmt != null && !pstmt.isClosed())
{
pstmt.close();
}
}
return obj;
}
} SqlSession.java Mybatis模拟接口（src/main/java/com/bjpowernode/practice/simulation目录下）
package com.bjpowernode.practice.simulation;
import java.util.List;
/**
*
* 模拟SqlSession
*
*/
public interface SqlSession
{
public T getMapper(Class clazz);
public List selectList(String query) throws Exception;
} SqlSessionFactory.java Mybatis模拟类（src/main/java/com/bjpowernode/practice/simulation目录下）
package com.bjpowernode.practice.simulation;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
/**
*
* 模拟SqlSessionFactory
*
*/
public class SqlSessionFactory
{
private InputStream configuration;
public SqlSession openSession() throws IOException
{
SqlSessionImpl session = new SqlSessionImpl();
loadConfigurations(session);
return session;
}
/**
*
* 通过Ｄｏｍ４ｊ读取配置文件信息
*
* @param session
* @throws IOException
*/
private void loadConfigurations(final SqlSessionImpl session) throws IOException
{
try
{
Document document = new SAXReader().read(configuration);
Element root = document.getRootElement();
List mappers = root.element("mappers").elements("mapper");
for (Element mapper : mappers)
{
if (mapper.attribute("resource") != null)
{
session.setXmlSQLs(loadXMLConfiguration(mapper.attribute("resource").getText()));
}
if (mapper.attribute("class") != null)
{
}
}
}
catch (Exception e)
{
System.out.println("读取配置文件错误!");
}
finally
{
configuration.close();
}
}
/**
*
* 通过ｄｏｍ４ｊ读取Ｍａｐｐｅｒ．ｘｍｌ中的信息
*
* @param resource
* @return
* @throws DocumentException
* @throws IOException
*/
private Map loadXMLConfiguration(String resource) throws DocumentException, IOException
{
Map map = new HashMap();
InputStream is = null;
try
{
is = this.getClass().getClassLoader().getResourceAsStream(resource);
Document document = new SAXReader().read(is);
Element root = document.getRootElement();
if (root.getName().equalsIgnoreCase("mapper"))
{
String namespace = root.attribute("namespace").getText();
for (Element select : (List) root.elements("select"))
{
Mapper mapperModel = new Mapper();
mapperModel.setResultType(select.attribute("resultType").getText());
mapperModel.setQuerySql(select.getText().trim());
map.put(namespace + "." + select.attribute("id").getText(), mapperModel);
}
}
}
finally
{
is.close();
}
return map;
}
public InputStream getConfiguration()
{
return configuration;
}
public void setConfiguration(InputStream configuration)
{
this.configuration = configuration;
}
} SqlSessionFactoryBuilder.java Mybatis模拟类（src/main/java/com/bjpowernode/practice/simulation目录下）
package com.bjpowernode.practice.simulation;
import java.io.InputStream;
/**
*
* 模拟SqlSessionFactoryBuilder
*
*/
public class SqlSessionFactoryBuilder
{
public SqlSessionFactory build(InputStream is)
{
SqlSessionFactory sessionFactory = new SqlSessionFactory();
sessionFactory.setConfiguration(is);
return sessionFactory;
}
} SqlSessionImpl.java Mybatis模拟类（src/main/java/com/bjpowernode/practice/simulation目录下）
package com.bjpowernode.practice.simulation;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
/**
*
* 模拟SqlSessionImpl
*
*/
public class SqlSessionImpl implements SqlSession
{
/** DB connection */
public static Connection connection;
private Map xmlSQLs;
private List annotationClasses;
public SqlSessionImpl()
{
/**
* driverString 和 connString 应该是从配置文件读取，这里简化了
*/
final String driverString = "org.apache.derby.jdbc.ClientDriver";
final String connString = "jdbc:derby://localhost:1527/bjpowernode;create=true";
try
{
Class.forName(driverString);
/** 获得DB连接 */
connection = DriverManager.getConnection(connString);
}
catch (Exception e)
{
System.out.println("获取DBConnection出错！");
}
}
/**
* 基于Annotation的数据库操作
*
*/
@Override
public T getMapper(Class clazz)
{
T clazzImpl =
(T) Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[] {clazz}, new SQLSelectProxy());
return clazzImpl;
}
/**
*
* 基于XML的查询操作
*/
@Override
public List selectList(String query) throws Exception
{
PreparedStatement pstmt = null;
ResultSet rs = null;
try
{
/** 简单的PreparedStateme JDBC实现 */
pstmt = connection.prepareStatement(xmlSQLs.get(query).getQuerySql());
rs = pstmt.executeQuery();
/** 执行查询操作 */
return executeQuery(rs, xmlSQLs.get(query).getResultType());
}
finally
{
if (!rs.isClosed())
{
rs.close();
}
if (!pstmt.isClosed())
{
pstmt.close();
}
}
}
/**
*
* 执行查询操作，并将查询到的结果与配置中的ResultType根据变量名一一对应，通过反射调用Set方法注入各个变量的值
*
* @param rs
* @param type
* @return
* @throws Exception
*/
public static List executeQuery(ResultSet rs, String type) throws Exception
{
int count = rs.getMetaData().getColumnCount();
List columnNames = new ArrayList();
for (int i = 1; i <= count; i++)
{
columnNames.add(rs.getMetaData().getColumnName(i));
}
final List list = new ArrayList UserMapper.xml 基于XML的Mapper配置文件（src/main/java/com/bjpowernode/practice/xml目录下）
<?xml version="1.0" encoding="UTF-8" ?>
TestMyBatis.java 测试类(src/test/java/com/bjpowernode/practice目录下)
package com.bjpowernode.practice;
import com.bjpowernode.practice.annotation.UserMapper;
import com.bjpowernode.practice.simulation.SqlSession;
import com.bjpowernode.practice.simulation.SqlSessionFactory;
import com.bjpowernode.practice.simulation.SqlSessionFactoryBuilder;
import com.bjpowernode.practice.simulation.SqlSessionImpl;
import java.io.InputStream;
import java.sql.SQLException;
import java.text.MessageFormat;
import java.util.List;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
public class TestMyBatis
{
/** 配置置文件 */
private String source;
private InputStream inputStream;
private SqlSessionFactory sqlSessionFactory;
@Before
public void setUp()
{
source = "test-mybatis-configuration.xml";
}
/**
*
* 基于XML格式配置的测试方法
*
*/
@Test
public void testXMLConfingure()
{
try
{
/**
* 获得Session
*/
inputStream = TestMyBatis.class.getClassLoader().getResourceAsStream(source);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession session = sqlSessionFactory.openSession();
/**
* 执行Ｑｕｅｒｙ操作
*/
List users = (List) session.selectList("com.bjpowernode.practice.UserMapper.getUser");
System.out.println("Query by XML configuration...");
/**
* 打印结果
*/
this.printUsers(users);
}
catch (Exception e)
{
e.printStackTrace();
}
}
/**
*
* 基于Annotation配置的测试方法
*
*/
@Test
public void testAnnotationConfingure()
{
try
{
inputStream = TestMyBatis.class.getClassLoader().getResourceAsStream(source);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession session = sqlSessionFactory.openSession();
UserMapper userMapper = session.getMapper(UserMapper.class);
System.out.println("\r\nQuery by annotation configuration...");
this.printUsers(userMapper.getUser());
}
catch (Exception e)
{
e.printStackTrace();
}
}
@After
public void clearUp() throws SQLException
{
if (SqlSessionImpl.connection != null && !SqlSessionImpl.connection.isClosed())
{
SqlSessionImpl.connection.close();
}
}
private void printUsers(final List users)
{
int count = 0;
for (User user : users)
{
System.out.println(MessageFormat.format("==User[{0}]=================", ++count));
System.out.println("User Id: " + user.getId());
System.out.println("User UserName: " + user.getUsername());
System.out.println("User Password: " + user.getPassword());
System.out.println("User nickname: " + user.getNickname());
}
}
} 以上就是基于XML以及Annotation的方式对Mybatis实现了一个简单的模拟。旨在理解Mybatis的工作原理。
笔者一直觉得当学习一个工具类技术的时候，路线应该是
1.实现一个小例子
2.找材料理解其中原理
3.学习技术细节，并动手全部实现
4.在全部学完之后动手做一个小项目，尽可能的使用这个在技术中的各个环节。
总结
以上所述是小编给大家介绍的模拟Mybatis的实现方法，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对创新互联网站的支持！
分享名称：模拟Mybatis的实现方法
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