Mybatis数据库文件配置是在项目启动时初始化数据工厂的，初始化过程仅为1次，当数据库地址改变时需修改配置文件重新启动项目，无法动态加载数据源。
Mybatis连接数据库底层核心库SqlSessionFactory，项目初始化也是生成该类，并缓存，该需求需要通过编程根据不同数据源动态生成SqlSessionFactory实例。
核心代码：
String driver="oracle.jdbc.driver.OracleDriver",url="jdbc:oracle:thin:@127.0.0.1:1521:orcl" ///mysql //driver = "com.mysql.jdbc.Driver" //url = "jdbc:mysql://"+hotel.getIp()+":"+hotel.getPort()+"/"+hotel.getDatabase() //初始化数据库属性 Properties properties = new Properties() properties.setProperty("jdbc.driver",driver) properties.setProperty("jdbc.url", url) properties.setProperty("jdbc.username",hotel.getUsername()) properties.setProperty("jdbc.password",hotel.getPassword()) Reader reader = Resources.getResourceAsReader(HotelFactory.configuration) //创建数据工厂 SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder() SqlSessionFactory sqlSessionFactory = builder.build(reader, properties) SqlSession sqlSession = sqlSessionFactory.openSession() HotelMapper hotelMapper = sqlSession.getMapper(HotelMapper.class) hotelMapper.getHotelById(1) //释放会话 sqlSession.clearCache() sqlSession.close()
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configuration.xml Mybatis配置文件
<?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> <typeAliases> </typeAliases> <environments default="HD"> <environment id="HD"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="poolMaximumActiveConnections" value="1000"/> <property name="driver" value="${jdbc.driver}" /> <property name="url" value="${jdbc.url}" /> <property name="username" value="${jdbc.username}" /> <property name="password" value="${jdbc.password}" /> </dataSource> </environment> </environments> <mappers> <mapper resource="mapper/HotelMapper.xml"/> <mapper resource="mapper/RestaurantMapper.xml"/> <mapper resource="mapper/RoomsMapper.xml"/> <mapper resource="mapper/MeetingsMapper.xml"/> </mappers></configuration>
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HotelMapper
<?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="mapper.HotelMapper"> <select id="getHotelById" resultType="entity.Hotel"> select * from HOTEL where ID = #{id,jdbcType=DECIMAL} </select></mapper> public interface HotelMapper { Hotel getHotelById(@Param("id") int id); }
SqlSessionFactory只是记载的数据库的连接属性，并未与数据库连接，并不占用数据库及系统资源。
SQLSession便于数据库建立连接了，每次读取数据后若不释放，数据库的连接数不断增加，当超过数据库的最大连接数或者内存溢出均会导致程序崩溃。
每次连接都需要初始化，过于麻烦，可封装套数据工厂，缓存相关信息。
设计思路1：缓存SqlSessionFactory，通过java动态代理释放数据库资源即SqlSession。（适用多点，SqlSession数量不可控情况）
设计思路2：缓存SqlSessionFactory及SqlSession，SqlSession会默认缓存已调用的方法，通过sqlSession.clearCache()清空默认缓存，保证读取的是实时数据库。（适用单点或少数站点机，SqlSession数量可控情况）
设计思路1核心代码：
数据工厂DataSourceFactory代码：
package factory;import java.io.Reader;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.net.InetSocketAddress;import java.net.Socket;import java.net.SocketAddress;import java.util.HashMap;import java.util.Map;import java.util.Properties;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import entity.Hotel;@SuppressWarnings("finally")public class DataSourceFactory { private static final int MaxDataSourceSize=10; private static final int TimeOut = 2000; private static Map<Integer,SqlSessionFactory> dataSoruce; static{ dataSoruce = new HashMap<Integer, SqlSessionFactory>(MaxDataSourceSize); } private static void removeFirstMap(){ for (Integer key : dataSoruce.keySet()) { dataSoruce.remove(key); break; } } public static void removeHotel(int hotelid){ dataSoruce.remove(hotelid); } public static boolean isConnection(Hotel hotel){ Boolean result = false; try{ Socket client = new Socket(); SocketAddress socketAddress = new InetSocketAddress(hotel.getIp(),Integer.parseInt(hotel.getPort())); client.connect(socketAddress,TimeOut); client.close(); result = true; } catch(Exception e){ e.printStackTrace(); result = false; } finally{ return result; } } public static boolean isConnection(Integer id){ Boolean result = false; try{ Hotel hotel = HotelFactory.getHotelById(id); if(hotel != null){ Socket client = new Socket(); SocketAddress socketAddress = new InetSocketAddress(hotel.getIp(),Integer.parseInt(hotel.getPort())); client.connect(socketAddress,TimeOut); client.close(); result = true; } } catch(Exception e){ e.printStackTrace(); result = false; } finally{ return result; } } private static SqlSessionFactory createSqlSessionFactory(Integer id){ SqlSessionFactory _sqlSessionFactory = null; try{ Hotel hotel = HotelFactory.getHotelById(id); if(hotel != null && isConnection(hotel)){ String driver="oracle.jdbc.driver.OracleDriver",url="jdbc:oracle:thin:@"+hotel.getIp()+":"+hotel.getPort()+":"+hotel.getSid(); Properties properties = new Properties(); properties.setProperty("jdbc.driver",driver); properties.setProperty("jdbc.url", url); properties.setProperty("jdbc.username",hotel.getUsername()); properties.setProperty("jdbc.password",hotel.getPassword()); Reader reader = Resources.getResourceAsReader(HotelFactory.configuration); SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder(); _sqlSessionFactory = builder.build(reader, properties); } } catch(Exception e){ e.printStackTrace(); } finally{ return _sqlSessionFactory; } } @SuppressWarnings("unchecked") public static <T> T getMapper(Integer id,Class<?> clazz){ if(isConnection(id)){ SqlSessionFactory sqlSessionFactory = dataSoruce.get(id); if(sqlSessionFactory==null){ sqlSessionFactory = createSqlSessionFactory(id); if(sqlSessionFactory != null){ if(dataSoruce.size()>=MaxDataSourceSize){ removeFirstMap(); } dataSoruce.put(id, sqlSessionFactory); } else return null; } SqlSession sqlSession = sqlSessionFactory.openSession(); Object idal = sqlSession.getMapper(clazz); return (T)IDALProxy.bind(idal, sqlSession); } else return null; } public static class IDALProxy implements InvocationHandler { private Object idal; private SqlSession sqlSession; private IDALProxy(Object idal, SqlSession sqlSession) { this.idal = idal; this.sqlSession = sqlSession; } public static Object bind(Object idal, SqlSession sqlSession) { return Proxy.newProxyInstance(idal.getClass().getClassLoader(),idal.getClass().getInterfaces(), new IDALProxy(idal, sqlSession)); } public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { Object object = null; try { object = method.invoke(idal, args); } catch(Exception e) { sqlSession.rollback(); e.printStackTrace(); } finally { sqlSession.commit(); sqlSession.clearCache(); sqlSession.close(); } return object; } }}
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酒店工厂HotelFactory代码：
package factory;import java.io.InputStream;import java.io.Reader;import java.util.Properties;import mapper.HotelMapper;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import entity.Hotel;public class HotelFactory { public static SqlSessionFactory sqlSessionFactory = null; public static final String jdbc_properties="jdbc.properties"; public final static String configuration = "configuration.xml"; static{ try { Properties properties = new Properties(); InputStream in = Resources.getResourceAsStream(jdbc_properties); properties.load(in); String driver = properties.getProperty("jdbc.driverClassName"); String url = properties.getProperty("jdbc.url"); String username = properties.getProperty("jdbc.username"); String password = properties.getProperty("jdbc.password"); properties.setProperty("jdbc.driver",driver); properties.setProperty("jdbc.url", url); properties.setProperty("jdbc.username",username); properties.setProperty("jdbc.password",password); Reader reader = Resources.getResourceAsReader(configuration); SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder(); sqlSessionFactory = builder.build(reader, properties); } catch (Exception e) { e.printStackTrace(); } } @SuppressWarnings("finally") public static Hotel getHotelById(Integer id){ Hotel hotel = null; SqlSession sqlSession = null; try{ sqlSession = sqlSessionFactory.openSession(); hotel = sqlSession.getMapper(HotelMapper.class).getHotelById(id); } catch(Exception e){ e.printStackTrace(); } finally{ if(sqlSession != null) sqlSession.close(); return hotel; } }}
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引用实例：
RoomsMapper roomMapper = getMapper(hotelid);roomMapper.getRoom();
Hotel实体中存了数据库的IP地址，端口号等基本信息，根据hotel生成对应库的Mapper实例进行数据操作。
通过IDALProxy类对生成Mapper实例的所有方法进行了再次封装，实现数据库资源的提交，缓存清空和释放。
