模拟Mybatis的实现方法

<dependency>  <groupId>junit</groupId>  <artifactId>junit</artifactId>  <version>4.9</version>  <scope>test</scope>  </dependency>  <dependency>  <groupId>org.apache.derby</groupId>  <artifactId>derby</artifactId>  <version>10.10.2.0</version>  </dependency>  <dependency>  <groupId>org.apache.derby</groupId>  <artifactId>derbyclient</artifactId>  <version>10.10.2.0</version>  </dependency>  <dependency>  <groupId>dom4j</groupId>  <artifactId>dom4j</artifactId>  <version>1.6.1</version>  </dependency> 

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'); 

test-mybatis-configuration.xml<?xml version="1.0" encoding="UTF-8" ?> <configuration>  <properties>  <property name="driver" value="org.apache.derby.jdbc.ClientDriver" />  <property name="url"  value="jdbc:derby://localhost:1527/bjpowernode;create=true" />  </properties>  <environments default="development">  <environment id="development">  <transactionManager type="JDBC" />  <dataSource type="POOLED">  <property name="driver" value="${driver}" />  <property name="url" value="${url}" />  </dataSource>  </environment>  </environments>  <mappers>  <mapper class="com.bjpowernode.practice.annotation.UserMapper" />  <mapper resource="com/bjpowernode/practice/xml/UserMapper.xml" />  </mappers> </configuration> 

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;  } } 

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(); } 

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<User> getUser(); } 

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;  } } 

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<com.bjpowernode.practice.User>  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;  } } 

package com.bjpowernode.practice.simulation; import java.util.List; /**  *  * 模拟SqlSession  *  */ public interface SqlSession {  public <T> T getMapper(Class<T> clazz);  public <E> List<E> selectList(String query) throws Exception; } 

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<Element> 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<String, Mapper> loadXMLConfiguration(String resource) throws DocumentException, IOException  {  Map<String, Mapper> map = new HashMap<String, Mapper>();  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<Element>) 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;  } } 

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;  } } 

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<String, Mapper> xmlSQLs;  private List<String> 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> T getMapper(Class<T> 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 <E> List<E> 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 <E> List<E> executeQuery(ResultSet rs, String type) throws Exception  {  int count = rs.getMetaData().getColumnCount();  List<String> columnNames = new ArrayList<String>();  for (int i = 1; i <= count; i++)  {  columnNames.add(rs.getMetaData().getColumnName(i));  }  final List list = new ArrayList<Object>();  while (rs.next())  {  Class modelClazz = Class.forName(type);  Object obj = modelClazz.newInstance();  for (Method setMethods : modelClazz.getMethods())  {  for (String columnName : columnNames)  {   if (setMethods.getName().equalsIgnoreCase("set" + columnName))   {   setMethods.invoke(obj, rs.getString(columnName));   }  }  }  list.add(obj);  }  return list;  }  public Map<String, Mapper> getXmlSQLs()  {  return xmlSQLs;  }  public void setXmlSQLs(Map<String, Mapper> xmlSQLs)  {  this.xmlSQLs = xmlSQLs;  }  public List<String> getAnnotationClasses()  {  return annotationClasses;  }  public void setAnnotationClasses(List<String> annotationClasses)  {  this.annotationClasses = annotationClasses;  } } 

<?xml version="1.0" encoding="UTF-8" ?>  <!-- namespace 当基于XML进行配置的时候是根据namespace+id来拼接进行SQL操作 --> <mapper namespace="com.bjpowernode.practice.UserMapper">  <!-- select 查询 -->  <select id="getUser" resultType="com.bjpowernode.practice.User">  select *  from USER_TEST_TB  </select> </mapper> 

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<User> 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<User> 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());  }  } }