发布于2020-12-03 06:05 阅读(1132) 评论(0) 点赞(4) 收藏(3)
本文主要介绍Java中,不使用XML和使用XML构建SqlSessionFactory,通过SqlSessionFactory 中获取SqlSession的方法,使用SqlsessionManager管理Sqlsession复用等等..以及相关的示例代码
SqlSessions 是由 SqlSessionFactory 实例创建的。SqlSessionFactory 对象包含创建 SqlSession 实例的各种方法。而 SqlSessionFactory 本身是由 SqlSessionFactoryBuilder 创建的,它可以从 XML、注解或 Java 配置代码来创建 SqlSessionFactory。
使用 MyBatis 的主要 Java 接口就是 SqlSession。你可以通过这个接口来执行命令,获取映射器示例和管理事务。在介绍 SqlSession 接口之前,我们先来了解如何获取一个 SqlSession 实例。
public class Ttest {
private Long id;
private String context;
....
}
TestMapper.java
public interface TestMapper {
Ttest getOne(Long id);
}
TestMapper.xml
<mapper namespace="com.liangtengyu.mapper.TestMapper">
<select id="getOne" resultType="com.liangtengyu.entity.Ttest">
select * from t_test where id = #{id}
</select>
</mapper>
mybatis-config.xml
<?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>
<!--开启日志输出-->
<settings>
<setting name="logImpl" value="STDOUT_LOGGING" />
</settings>
<!--配置类别名,配置后在Mapper配置文件(通常我们将编写SQL语句的配置文件成为Mapper配置文件)中需要使用pojo包中的类时,使用简单类名即可-->
<typeAliases>
<package name="com.liangtengyu.entity"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
<property name="url" value="jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8"/>
</dataSource>
</environment>
</environments>
<mappers>
<package name="com.liangtengyu.mapper"/>
</mappers>
</configuration>
来个测试方法:
@Test
public void testMyBatisBuild() throws IOException {
Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
SqlSession sqlSession = factory.openSession();
TestMapper mapper = sqlSession.getMapper(TestMapper.class);
Ttest one = mapper.getOne(1L);
System.out.println(one);
sqlSession.close();
}
运行测试方法,控制台打印日志:
Checking to see if class com.liangtengyu.mapper.TestMapper matches criteria [is assignable to Object]
Opening JDBC Connection
Created connection 2083117811. //创建的连接名
Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@7c29daf3]
==> Preparing: select * from t_test where id = ?
==> Parameters: 1(Long)
<== Columns: id, context
<== Row: 1, 123
<== Total: 1
Ttest{id=1, context='123'}
Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@7c29daf3]
Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@7c29daf3]
Returned connection 2083117811 to pool. //用完了又放回连接池中
SqlSessionFactoryBuilder 创建出SqlSessionFactory,然后从SqlSessionFactory中得到SqlSession,最后通过SqlSession得到Mapper接口对象进行数据库操作。
我们打个断点.来跟踪SqlSessionFactoryBuilder的源代码:
F7跟进 发现一堆build 而我们现在用的是传入reader的那个方法
我们可以看到,他帮我们传了2个Null参数给下一个build,我们跟着这个build继续往下跟.
这个build会将xml解析.然后调用parser.parse()方法将xml转化成Configuration,传入下一个build
继续下一个build
这个build终于干了我们最关心的事,他创建了DefaultSqlSessionFactory 返回SqlSessionFactory.
我们进来看看这个类:
public class DefaultSqlSessionFactory implements SqlSessionFactory {
//它是SqlSessionFactory的实现类.
private final Configuration configuration;
//通过传入一个Configuration 来构造
public DefaultSqlSessionFactory(Configuration configuration) {
this.configuration = configuration;
}
...
这样一看,那我们直接给它来个configuration不就可以创建一个SqlSessionFactory吗.
我们来试试
//使用传入Configuration方式创建SqlSessionFactoryBuilder
@Test
public void testMyBatisBuild1() throws IOException {
DataSource datasource = getDatasource();//首先创建数据源
Environment e = new Environment("test", new JdbcTransactionFactory(), datasource);//传入datasource和JdbcTransactionFactory
Configuration configuration = new Configuration();//构建一个Configuration
configuration.setEnvironment(e);
configuration.setLogImpl(StdOutImpl.class);//使用控制台输出日志实现
configuration.getTypeAliasRegistry().registerAlias(Ttest.class);
configuration.addMapper(TestMapper.class);
//传入configuration
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(configuration);
SqlSession sqlSession = build.openSession();
TestMapper mapper = sqlSession.getMapper(TestMapper.class);
Ttest one = mapper.getOne(1L);
System.out.println(one);
sqlSession.close();
}
//获取数据源方法
public UnpooledDataSource getDatasource(){
UnpooledDataSource unpooledDataSource = new UnpooledDataSource();
unpooledDataSource.setUrl("jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8");
unpooledDataSource.setDriver("com.mysql.jdbc.Driver");
unpooledDataSource.setUsername("root");
unpooledDataSource.setPassword("123456");
return unpooledDataSource;
}
运行结果:
Logging initialized using 'class org.apache.ibatis.logging.stdout.StdOutImpl' adapter.
Opening JDBC Connection
Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@3dd4520b]
==> Preparing: select * from t_test where id = ?
==> Parameters: 1(Long)
<== Columns: id, context
<== Row: 1, 123
<== Total: 1
Ttest{id=1, context='123'}
Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@3dd4520b]
Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@3dd4520b]
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(configuration);
//在构造SqlSessionFactory时实际调用的还是DefaultSqlSessionFactory 所以我们直接使用
DefaultSqlSessionFactory factory = new DefaultSqlSessionFactory(configuration);
//也是一样的效果
那么他的内部是如何创建session的我们来看看源代码
根据断点我们到了factory.opensession()方法 F7进入方法
F8单步 发现调用了openSessionFromDataSource方法
三个参数.第一个参数是configuration.getDefaultExecutorType()
这个参数是Configuration类中定义的默认类型.
package org.apache.ibatis.session;
//还有其它 的类型 如下.
/**
* @author Clinton Begin
*/
public enum ExecutorType {
SIMPLE, REUSE, BATCH
}
大家可能对 ExecutorType 参数感到陌生。这个枚举类型定义了三个值:
ExecutorType.SIMPLE
:该类型的执行器没有特别的行为。它为每个语句的执行创建一个新的预处理语句。
ExecutorType.REUSE
:该类型的执行器会复用预处理语句。
ExecutorType.BATCH
:该类型的执行器会批量执行所有更新语句,如果 SELECT 在多个更新中间执行,将在必要时将多条更新语句分隔开来,以方便理解。这里不再深入讨论
是称为 TransactionIsolationLevel,
事务隔离级别支持 JDBC 的五个隔离级别(NONE
、READ_UNCOMMITTED
、READ_COMMITTED
、REPEATABLE_READ
和 SERIALIZABLE
),并且与预期的行为一致。
向 autoCommit 可选参数传递 true 值即可开启自动提交功能
继续往下 进到openSessionFromDataSource方法
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
final Environment environment = configuration.getEnvironment();
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
final Executor executor = configuration.newExecutor(tx, execType);
return new DefaultSqlSession(configuration, executor, autoCommit);//返回DefaultSqlSession
} catch (Exception e) {
closeTransaction(tx); // may have fetched a connection so lets call close()
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
返回的DefaultSqlSession实现了SqlSession的所有方法
我们进入到Sqlsession类中查看一下实现它的都有哪些类
一共有两个,而且SqlSessionManager还实现了SqlSessionFactory
public class SqlSessionManager implements SqlSessionFactory, SqlSession {
private final SqlSessionFactory sqlSessionFactory;
private final SqlSession sqlSessionProxy;//这里使用了代理,来增强sqlsession
private final ThreadLocal<SqlSession> localSqlSession = new ThreadLocal<>();
//使用Threadlocal管理本线程的sqlsession来复用sqlsession
private SqlSessionManager(SqlSessionFactory sqlSessionFactory) {
this.sqlSessionFactory = sqlSessionFactory;
this.sqlSessionProxy = (SqlSession) Proxy.newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[]{SqlSession.class},
new SqlSessionInterceptor());
}
//这个方法帮我们直接创建了sqlSessionFactory并且将传入的sqlSessionFactory的SqlSession进行了代理
public static SqlSessionManager newInstance(Reader reader) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, null, null));
}
.....
public static SqlSessionManager newInstance(Reader reader) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, null, null));
}
public static SqlSessionManager newInstance(Reader reader, String environment) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, environment, null));
}
public static SqlSessionManager newInstance(Reader reader, Properties properties) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, null, properties));
}
public static SqlSessionManager newInstance(InputStream inputStream) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, null, null));
}
public static SqlSessionManager newInstance(InputStream inputStream, String environment) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, environment, null));
}
public static SqlSessionManager newInstance(InputStream inputStream, Properties properties) {
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, null, properties));
}
public static SqlSessionManager newInstance(SqlSessionFactory sqlSessionFactory) {
return new SqlSessionManager(sqlSessionFactory);
}
.....
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { //使用Threadlocal管理本线程的sqlsession来复用sqlsession
final SqlSession sqlSession = SqlSessionManager.this.localSqlSession.get();
if (sqlSession != null) {//获取本线程的sqlsession
try {
return method.invoke(sqlSession, args);//实际调用
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
} else {
try (SqlSession autoSqlSession = openSession()) {
try {
final Object result = method.invoke(autoSqlSession, args);
autoSqlSession.commit();
return result;
} catch (Throwable t) {
autoSqlSession.rollback();
throw ExceptionUtil.unwrapThrowable(t);
}
}
}
}
SqlSessionManager
他实现了Session接口。意味着,SqlSessionManager集成了 sqlSessionFactory和session 的功能。通过SqlSessionManager,开发者可以不在理会SqlSessionFacotry的存在,直接面向Session编程。
SqlSessionManager 内部提供了一个sqlSessionProxy,这个sqlSessionProxy提供了所有Session接口的实现,而实现中正是使用了上面提到的本地线程保存的session实例。
这样,在同一个线程实现不同的sql操作,可以复用本地线程session,避免了DefaultSqlSessionFactory实现的每一个sql操作都要创建新的session实例
下面让我们用一个简单的实例来试试
@Test
public void testMyBatisBuild3() throws IOException {
Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
// SqlSessionFactory build = new SqlSessionFactoryBuilder().build(reader);
// 不使用SqlSessionFactory 使用SqlSessionManager.newInstance();
SqlSessionManager sqlSessionManager = SqlSessionManager.newInstance(reader);
SqlSession sqlSession = sqlSessionManager.openSession();
TestMapper mapper = sqlSession.getMapper(TestMapper.class);
Ttest one = mapper.getOne(1L);
System.out.println(one);
sqlSession.close();
}
运行结果:
Reader entry: ����1 getOne0(Ljava/lang/Long;)Lcom/liangtengyu/entity/Ttest;
Find JAR URL: file:/Users/tengyu/IdeaProjects/mybatis-study/target/classes/com/liangtengyu/mapper/TestMapper.xml
Not a JAR: file:/Users/tengyu/IdeaProjects/mybatis-study/target/classes/com/liangtengyu/mapper/TestMapper.xml
Reader entry: <?xml version="1.0" encoding="UTF-8"?>
Checking to see if class com.liangtengyu.mapper.TestMapper matches criteria [is assignable to Object]
Opening JDBC Connection
Created connection 1585787493.
Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@5e853265]
==> Preparing: select * from t_test where id = ?
==> Parameters: 1(Long)
<== Columns: id, context
<== Row: 1, 123
<== Total: 1
Ttest{id=1, context='123'}
Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@5e853265]
Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@5e853265]
Returned connection 1585787493 to pool.
本章主要讲了MyBatis构建SqlSessionFactory方式,过程,和sqlsession的创建,以及使用SqlSessionManager管理session复用的实现方式.
下一篇研究数据源的池化和数据源加载过程.
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