Mybatis初步
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MyBatis 是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。
1.准备开发环境
1、创建测试项目，普通java项目或者是JavaWeb项目均可，如下图所示： 
添加相应的jar包：
mybatis-3.4.4.jar
mysql-connector-java-5.1.30-bin.jar
jsbc.prop[mysql数据库信息配置文件]：
#dbConfig#Mon Jul 31 07:54:49 CST 2017url=jdbc:mysql://localhost:3306/t_marketpassword=rootdriver=com.mysql.jdbc.Driverusername=rootmybatis-config.xml[mybatis配资信息文件]:
<?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> <!-- properties属性,properties和java的.properties的配置文件有关; 配置properties的resource指定.properties的路径; 然后再在properties标签下配置property的name和value， 则可以替换.properties文件中相应属性值。 --> <properties resource="jsbc.prop" /> <!--typeAliases 必须在properties之后声明 --> <!-- typeAliases类型别名,类型别名是Java 类型的简称;它仅仅只是关联到XML 配置，简写冗长的JAVA 类名; --> <typeAliases> <!-- 定义别名User为javaBean类com.my.market.model.User --> <typeAlias alias="User" type="com.my.market.model.User"/> </typeAliases><!-- environments环境,MyBatis 可以配置多个环境。这可以帮助你SQL 映射对应多种数据库等; --> <environments default="development"> <!-- 默认开发环境 --> <environment id="development"> <!-- 事务管理器 --> <transactionManager type="JDBC"/> <!-- 数据源 --> <dataSource type="POOLED"> <property name="driver" value="${driver}"/> <property name="url" value="${url}"/> <property name="username" value="${username}"/> <property name="password" value="${password}"/> </dataSource> </environment> </environments> <!-- 将model中类对应的mapper文件加入配置中--> <!-- mappers映射器,这里是告诉MyBatis 去哪寻找映射SQL 的语句;可以使用类路径中的资源引用，或者使用字符，输入确切的URL引用; --> <mappers> <mapper resource="com/my/market/model/User.xml"/> </mappers></configuration> 2.定义表所对应的实体类，如下图所示：
User.java[实体类User]:
package com.my.market.model;public class User { private int id; private String username; private String password; private String nickname; private int type; 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; } public int getType() { return type; } public void setType(int type) { this.type = type; } public int getId() { return id; } public String getUsername() { return username; } public User(int id, String username, String password, String nickname, int type) { this.id = id; this.username = username; this.password = password; this.nickname = nickname; this.type = type; } public User() { } @Override public String toString() { return "User [id=" + id + ", username=" + username + ", password=" + password + ", nickname=" + nickname + ", type=" + type + "]"; }}User.xml[User类对应的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"><!-- com.my.market.model.User实体类对应的mapper文件，namespace限定名字空间避免重复 --><mapper namespace="com.my.market.model.User"> <!-- 通过[namespace.id 即 com.my.market.model.User.add]进行add的插入方法的调用 --> <insert id="add" parameterType="User"> insert into t_user(username, password, nickname, type) values(#{username},#{password},#{nickname},#{type}) </insert> <update id="update" parameterType="User"> update t_user set password=#{password},nickname=#{nickname},type=#{type} where id=#{id} </update> <delete id="delete" parameterType="int"> delete from t_user where id=#{id} </delete> <select id="select" parameterType="int" resultType="User"> select * from t_user where id=#{id} </select> <!-- 使用User别名 --> <select id="list" resultType="User"> select * from t_user </select></mapper>3.Junit测试类
MyBatisUtil.java[Mybatis工具类用来获取session]:
package com.my.market.util;import java.io.Closeable;import java.io.IOException;import java.io.InputStream;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;public class MyBatisUtil { private static final String RESOURCE = "mybatis-config.xml"; private static SqlSessionFactory factory; static { try { //1.创建配置文件(mybatis-config.xml)的输入流 InputStream iStream=Resources.getResourceAsStream(RESOURCE); //2.创建SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(iStream); } catch (IOException e) { e.printStackTrace(); } } private MyBatisUtil() { } public static SqlSession getSession() { //3.创建SqlSession return factory.openSession(); } public static void close(SqlSession session) { if(null!=session) { session.close(); } }}TestMyBatisJunit.java[MyBatis Junit测试类]:
package com.my.market.test;import static org.junit.Assert.*;import java.io.IOException;import java.io.InputStream;import java.util.List;import javax.jws.soap.SOAPBinding.Use;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 org.junit.Test;import com.my.market.model.User;import com.my.market.util.MyBatisUtil;public class TestMyBatisJunit { private static final String RESOURCE = "mybatis-config.xml"; @Test public void testDelete() { InputStream is=null; try { is = Resources.getResourceAsStream(RESOURCE); } catch (IOException e) { e.printStackTrace(); } SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(is); SqlSession session=factory.openSession(); System.out.println(User.class.getName()); session.delete(User.class.getName()+".delete", 9); session.commit(); session.close(); } @Test public void testLoad() { SqlSession session=null; try { session=MyBatisUtil.getSession(); User user=(User)session.selectOne(User.class.getName()+".select", 1); System.out.println(user); }finally { MyBatisUtil.close(session); } } @Test public void testAdd() { SqlSession session=null; try { session=MyBatisUtil.getSession(); User user=new User(0, "tangseng1", "123", "唐僧1", 0); session.insert(User.class.getName()+".add", user); session.commit(); }catch(Exception e) { session.rollback(); e.printStackTrace(); } finally { session.close(); } } @Test public void testList() { SqlSession session=null; try { session=MyBatisUtil.getSession(); List<User> userList=session.selectList(User.class.getName()+".list"); for(User u: userList) { System.out.println(u); } }finally { MyBatisUtil.close(session); } }}4.工具，基础类
1.BaseDao.java[所有dao的基本父类]:
package com.my.market.dao;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.Arrays;import java.util.HashMap;import java.util.List;import java.util.Map;import org.apache.ibatis.session.SqlSession;import com.my.market.model.Address;import com.my.market.model.Page;import com.my.market.model.SystemContext;import com.my.market.model.User;import com.my.market.util.DBUtil;import com.my.market.util.DaoUtil;import com.my.market.util.LogUtil;import com.my.market.util.MyBatisUtil;public class BaseDao<T> { public BaseDao() {// //依赖注入,对于子类需要set的对象,例如setUserDao// Method[] methods=this.getClass().getDeclaredMethods();// //error:unknow function// //this.setUserDao(null);// System.out.println(Arrays.toString(methods));// for(Method m: methods) {// String methodName =m.getName();// if(methodName.startsWith("set")) {// LogUtil.printLog(m);// String name=methodName.substring(3);// LogUtil.printLog(methodName+": "+name);// Object obj=DaoUtil.createDaoFactory().getDao(name);// try {// m.invoke(this, obj);// } catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {// e.printStackTrace();// }// }// } DaoUtil.diDao(this); } public void add(T obj) { SqlSession session=null; try { session=MyBatisUtil.getSession(); session.insert(obj.getClass().getName()+".add", obj); session.commit(); }catch(Exception e) { session.rollback(); e.printStackTrace(); }finally { MyBatisUtil.close(session); } } public <Type> void add(String sqlId, Type obj) { SqlSession session=null; try { session=MyBatisUtil.getSession(); session.insert(sqlId, obj); session.commit(); }catch(Exception e) { session.rollback(); e.printStackTrace(); }finally { MyBatisUtil.close(session); } } public void update(T obj) { SqlSession session=null; try { session=MyBatisUtil.getSession(); session.update(obj.getClass().getName()+".update", obj); session.commit(); }catch(Exception e) { session.rollback(); e.printStackTrace(); }finally { MyBatisUtil.close(session); } } public void delete(Class<T> clz, int id) { SqlSession session=null; try { session=MyBatisUtil.getSession(); session.delete(clz.getName()+".delete", id); session.commit(); }catch(Exception e){ session.rollback(); e.printStackTrace(); }finally { MyBatisUtil.close(session); } } public void delete(String sqlId, Map<String, Object> params) { SqlSession session=null; try { session=MyBatisUtil.getSession(); session.delete(sqlId, params); session.commit(); }catch(Exception e){ session.rollback(); e.printStackTrace(); }finally { MyBatisUtil.close(session); } } public T load(Class<T> clz, int id) { SqlSession session=null; T obj=null; try { session=MyBatisUtil.getSession(); obj= session.selectOne(clz.getName()+".load", id); }finally { MyBatisUtil.close(session); } return obj; } public T loadBySqlId(String sqlId, Map<String, Object> params) { SqlSession session=null; T obj=null; try { session=MyBatisUtil.getSession(); obj= session.selectOne(sqlId, params); }finally { MyBatisUtil.close(session); } return obj; } public T loadBySqlId(String sqlId, Object param) { SqlSession session=null; T obj=null; try { session=MyBatisUtil.getSession(); obj= session.selectOne(sqlId, param); }finally { MyBatisUtil.close(session); } return obj; } public Page<T> find(Class<T> clz, Map<String, Object> params){ int pageSize =SystemContext.getMaxPageItems(); int pagerOffset=SystemContext.getPagerOffset(); String order=SystemContext.getOrder(); String condition=SystemContext.getCondition(); Page<T> page = null; SqlSession session=null; try { session=MyBatisUtil.getSession(); if(null==params) { params=new HashMap<>(); } params.put("pageSize", pageSize); params.put("pagerOffset", pagerOffset); params.put("order", order); params.put("condition", condition); List<T> objList=session.selectList(clz.getName()+".find", params); int totalRecord=session.selectOne(clz.getName()+".find_count", params); page=new Page<T>(pagerOffset/pageSize+1, totalRecord, pageSize, totalRecord/pageSize+(totalRecord%pageSize==0? 0:1), objList); }finally { MyBatisUtil.close(session); } return page; } public Page<T> find(String sqlId, Map<String, Object> params){ int pageSize =SystemContext.getMaxPageItems(); int pagerOffset=SystemContext.getPagerOffset(); String order=SystemContext.getOrder(); String condition=SystemContext.getCondition(); Page<T> page = null; SqlSession session=null; try { session=MyBatisUtil.getSession(); if(null==params) { params=new HashMap<>(); } params.put("pageSize", pageSize); params.put("pagerOffset", pagerOffset); params.put("order", order); params.put("condition", condition); List<T> objList=session.selectList(sqlId, params); LogUtil.printLog(sqlId); LogUtil.printLog(sqlId+"_count"); int totalRecord=session.selectOne(sqlId+"_count", params); page=new Page<T>(pagerOffset/pageSize+1, totalRecord, pageSize, totalRecord/pageSize+(totalRecord%pageSize==0? 0:1), objList); }finally { MyBatisUtil.close(session); } return page; } public List<T> listBySqlId(String sqlId, Map<String, Object> params){ List<T> objList= null; SqlSession session=null; try { session=MyBatisUtil.getSession(); if(null==params) { params=new HashMap<>(); } objList=session.selectList(sqlId, params); }finally { MyBatisUtil.close(session); } return objList; }}2.DaoUtil.java[工厂模式的获取，依赖注入]:
package com.my.market.util;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.Properties;import com.my.market.dao.IFactoryDao;import com.my.market.model.MarketDi;public class DaoUtil { public static void main(String[] args) { createDaoFactory(); } public static IFactoryDao createDaoFactory() { Properties properties= PropertiesUtil.getDaoProp(); String factoryName=properties.getProperty("factory"); LogUtil.printLog(factoryName); IFactoryDao daoFactory=null; try { Class<?> clz=Class.forName(factoryName); String methodName="getInstance"; Method method=clz.getMethod(methodName); daoFactory =(IFactoryDao)method.invoke(clz); } catch (ClassNotFoundException | NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) { // TODO Auto-generated catch block e.printStackTrace(); } LogUtil.printLog(daoFactory); return daoFactory; } public static void diDao(Object obj) { //get the class from the object which will set value into it Class<?> clz=obj.getClass(); //get declared methods from the class Method[] methods=clz.getDeclaredMethods(); for(Method m: methods) { //if the Method has 'MarketDi' annotation, it show the Method want to get a object if(m.isAnnotationPresent(MarketDi.class)) { MarketDi aDi=m.getAnnotation(MarketDi.class); String objName=aDi.value(); if(null==objName || "".equals(objName)) { String methodName=m.getName(); LogUtil.printLog(methodName+": "+objName); if(methodName.startsWith("set")) { LogUtil.printLog(m); objName=methodName.substring(3); } } //get className from properties file, invoke the Method, set the object into it try { Properties properties=PropertiesUtil.getDaoProp(); String className=properties.getProperty(objName); LogUtil.printLog(objName+": "+className); Object object=Class.forName(className).newInstance(); m.invoke(obj, object); } catch (InstantiationException | IllegalAccessException | ClassNotFoundException | IllegalArgumentException | InvocationTargetException e) { e.printStackTrace(); } } } }}3.PropertiesUtil.java[属性读取工具]:
package com.my.market.util;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.util.Properties;import sun.security.jca.GetInstance;public class PropertiesUtil { private static Properties dBProperties=null; private static Properties daoProperties=null; private static final String CONFIG_FILE="dbConfi.prop"; private static final String DAO_FILE="dao.prop"; private PropertiesUtil() { } public static Properties getInstance() { if(null==dBProperties) { synchronized (PropertiesUtil.class) { if(null==dBProperties) { dBProperties=new Properties();// try(// FileInputStream fin=new FileInputStream("/"+CONFIG_FILE);// ){ try{ File f1=new File("test.txt"); LogUtil.printLog(f1.getAbsolutePath()); LogUtil.printLog(PropertiesUtil.class.getResource(CONFIG_FILE)); dBProperties.load(PropertiesUtil.class.getResourceAsStream(CONFIG_FILE)); }catch (Exception e) { e.printStackTrace(); System.exit(-1); } } } } return dBProperties; } public static Properties getDaoProp() { try { if(null==daoProperties) { synchronized(PropertiesUtil.class) { if(null==daoProperties) { daoProperties=new Properties(); daoProperties.load(PropertiesUtil.class.getClassLoader().getResourceAsStream(DAO_FILE)); } } } }catch(IOException e) { e.printStackTrace(); } return daoProperties; }}DaoFactoryByProperties.java[通过properties获取Dao工厂]:
package com.my.market.dao;import java.util.HashMap;import java.util.Map;import java.util.Properties;import com.my.market.util.LogUtil;import com.my.market.util.PropertiesUtil;public class DaoFactoryByProperties implements IFactoryDao { private static DaoFactoryByProperties factory=new DaoFactoryByProperties(); private static Map<String, Object> daoMap=new HashMap<>(); private DaoFactoryByProperties() { } public static IFactoryDao getInstance() { return factory; } @Override public Object getDao(String name) { Object object=null; Properties properties=PropertiesUtil.getDaoProp(); String daoClassName=properties.getProperty(name); LogUtil.printLog(daoClassName); if(daoMap.containsKey(daoClassName)) { return daoMap.get(daoClassName); } try { object=Class.forName(daoClassName).newInstance(); daoMap.put(daoClassName, object); } catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) { e.printStackTrace(); } return object; }}5.mybatis使用步骤
操作步骤
1、将jar导入到项目
2、创建Config.xml文件用来指定相应的数据库连接信息 
3、创建mapp.xml文件 
4、创建SqlSessionFactory 
5、根据factory获取session 
6、直接根据session来执行相应的操作
6.map文件中的insert,update,delete,select
insert标签表示添加相应的对象信息,paramterType表示添加的对象类型 
update表示更新操作，delete表示删除操作 
select表示查询操作，可以查询列表或者单个对象 
相应的调用方式
7.mapp.xml中两种引用
1、#{xxx}这种方式会自动将这个值替换为PreparedStatment中?来使用，如果是字符串会自动加上引号，对于排序而言就无法操作
2、${xx}这种方式叫做完全替换，直接将字符串完整的替换到这个位置，完全替换的方式可能会出现SQL注入的安全隐患。建议在参数中不要使用这种方式。但是如果使用在排序中没有任何影响
8.动态SQL语句
在mapp.xml文件中可能会根据一些参数值的不同而动态的产生相应的SQL语句，此时就需要进行动态SQL语句的设定
9.Resultmap的使用
使用ResultMap可以完成相应的结果集自定义输出 
ResultMap还可以完成一些外键对对象的映射 
使用以上映射方式有一个致命的缺点：所谓的N+1问题
使用关联查询来解决N+1问题
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