时间：2021-07-01 10:21:17 帮助过：4人阅读
每一个Mybatis的应用程序都以一个SqlSessionFactory对象的实例为核心。SqlSessionFactory对象实例可以通过SqlSessionFactoryBuilder对象获得。SqlSessionFactoryBuilder对象可以从XML配置文件或从Configuration类的习惯准备的实例中构建SqlSessionFactory对象。
从XML文件中构建SqlSessionFactory的实例非常简单。这里建议使用类的路径的资源文件来配置，这样我们就可以使用任意的Reader实例，这个实例包括有文字形式的文件路径或URL形式的文件路径file：//来创建。Mybatis包含了一些工具类，称作为资源，这些工具类包含一些方法，这些方法使得从类路径或其他位置加载资源文件更加简单。
<span style="font-size:18px;">String resource = "org/mybatis/example/mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);</span>
<span style="font-size:18px;"><?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>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<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>
<mappers>
<mapper resource="org/mybatis/example/BlogMapper.xml"/>
</mappers>
</configuration></span>
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
但是事实上，SQLSessionFactoryBuilder类负责构建SqlSessionFactory，并且提供了多个build的重载方法，丹其实很多都是在调用同意签名的方法，例如public SqlSessionFactory build（InputStream inputStream，String environment，Properties properties），只是由于方法参数environment和properties都可以为null，所以为了提供调用的便利性，才提供了下面的三个方法。
<span style="font-size:18px;">public SqlSessionFactory build(InputStream inputStream) public SqlSessionFactory build(InputStream inputStream, String environment) public SqlSessionFactory build(InputStream inputStream, Properties properties)</span>
<span style="font-size:18px;">public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) public SqlSessionFactory build(Reader reader, String environment, Properties properties) public SqlSessionFactory build(Configuration config)</span>
（1）读取XML文件构造方式
<span style="font-size:18px;">String resource = "org/mybatis/example/mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream) ;</span>
<span style="font-size:18px;">DataSource dataSource = BlogDataSourceFactory.getBlogDataSource();
TransactionFactory transactionFactory = new JdbcTransactionFactory();
Environment environment = new Environment("development", transactionFactory, dataSource);
Configuration configuration = new Configuration(environment);
configuration.addMapper(BlogMapper.class);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration) ;</span>
<span style="font-size:18px;">public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
try {
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
inputStream.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}</span>通过上面的几行代码，就能看出基于XML文件的这种构造方式，通过XML读取信息的工作之后，也是构造出Configuration对象之后，再继续进行SqlSessionFactory的构建工作的，只是多了些XML的解析工作，所以我们只需要单钩植入，直接分析变成构造方式的代码就可以了，或者是直接分析build（Parser.parse()）这句代码
<span style="font-size:18px;"> public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}</span>
以上代码使用了一个设计模式：建设者模式（Builder)，SqlSessionFactoryBuilder扮演具体的建造者，Configuration类则负责建造的细节工作，SqlSession则是建造出来的产品。
看一下类图和创建者模式的基本形态图：
目录结构：
Goods：
<span style="font-size:18px;">package com.csdn.kane.domain;
import java.sql.Timestamp;
public class Goods {
private int id;
private int categoryId;
private String name;
private float price;
private String description;
private int acount;
private Timestamp updateTime;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getCategoryId() {
return categoryId;
}
public void setCategoryId(int categoryId) {
this.categoryId = categoryId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public float getPrice() {
return price;
}
public void setPrice(float price) {
this.price = price;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public int getAcount() {
return acount;
}
public void setAcount(int acount) {
this.acount = acount;
}
public Timestamp getUpdateTime() {
return updateTime;
}
public void setUpdateTime(Timestamp updateTime) {
this.updateTime = updateTime;
}
}
</span>GoodsMapper：
<span style="font-size:18px;">package com.csdn.kane.dao;
import org.apache.ibatis.annotations.Select;
import com.csdn.kane.domain.Goods;
public interface GoodsMapper {
@Select("SELECT * FROM Goods WHERE id=#{id}")
public Goods selectGoods(int id);
}
</span>
<span style="font-size:18px;"><?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>
<typeAlias alias="Goods" type="com.csdn.kane.domain.Goods"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<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 class="com.csdn.kane.dao.GoodsMapper"/>
</mappers>
</configuration> </span>
<span style="font-size:18px;">package com.csdn.kane.test;
import java.io.IOException;
import java.io.InputStream;
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 com.csdn.kane.dao.GoodsMapper;
import com.csdn.kane.domain.Goods;
public class TestMybitas {
public static void main(String[] args) throws IOException {
//最基本的mybitas示例方法
TestMybitas.testMethod();
}
public static void testMethod() throws IOException{
String resource = "applicationContext.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
Properties properties = new Properties();
properties.setProperty("jdbc.driver", "com.mysql.jdbc.Driver");
properties.setProperty(
"jdbc.url",
"jdbc:mysql://localhost:3306/qmxtest1?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true");
properties.setProperty("jdbc.username", "root");
properties.setProperty("jdbc.password", "root");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream,properties);
SqlSession session = sqlSessionFactory.openSession();
try {
GoodsMapper mapper = session.getMapper(GoodsMapper.class);
Goods goods = mapper.selectGoods(1);
System.out.println("good description:"+goods.getDescription());
} finally {
session.close();
}
}
}
</span>
Mybatis 动态切换数据库
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