从底层源码浅析Mybatis的SqlSessionFactory初始化过程

第一步: 将全局配置文件XML加载到Configuration对象
• 第二步 : 解析映射配置文件XML到Configuration的mapperRegistry容器
• 第三步 : 解析映射文件的Statement为MappedStatement对象
• 初始化完成

搭建源码环境

POM依赖

<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.5</version>
</dependency>

测试SQL

CREATE TABLE `user` (
`id` int(10) NOT NULL AUTO_INCREMENT,
`username` varchar(10) NOT NULL,
`password` varchar(52) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=latin1

Mybatis全局配置文件

<?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>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/test"/>
<property name="username" value="root"/>
<property name="password" value="jimisun"/>
</dataSource>
</environment>
</environments>

<mappers>
<mapper resource="mapper/UserMapper.xml"/>
</mappers>

</configuration>

UserMapper接口

public interface UserMapper {
User selectUser(Integer id);
}

UserMapper配置

<?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="user">
<select id="selectUser" resultType="com.jimisun.mybatis.domain.User">
select *
from user
where id = #{id}
</select>
</mapper>

User实体

public class User {
private int id;
private String username;
private String password;
getter and setter .....
}

Main方法

public static void main(String[] args) throws IOException {

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

SqlSession sqlSession = sqlSessionFactory.openSession();
User user = sqlSession.selectOne("user.selectUser", 2);
System.out.println(user.toString());

}

快速进入Debug跟踪

我们可以在此处打上断点,Debug模式启动进入断点,再按F7跟踪入其方法

源码分析准备

在进行Mybatis的初始化过程之前,我们需要把整个大纲拎出来放在前面,让大家能够有所了解,然后在进行每个步骤的时候心里有个大概;

• 什么是Mybatis的初始化过程?

• 浅析一词含义

• Mybatis初始化过程中的主要步骤 将全局配置文件XML解析到Configuration对象
• 将映射配置文件XML解析到Configuration的mapperRegistry对象
• 将映射配置文件XML中的声明(Statement)解析成MappedStatement对象存入Configuration对象的mappedStatements集合中
• 最后将Configuration最为参数构建DefaultSqlSessionFactory对象

源码分析

第一步: 将全局配置文件XML加载到Configuration对象

XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
parser.parse();

主要功能 : 将全局配置文件中的配置加载到一个Configuration对象的属性中

这是第一步,我们从

Main

new SqlSessionFactoryBuilder().build(inputStream)

SqlSessionFactoryBuilder

build

//SqlSessionFactoryBuilder的构造方法
public SqlSessionFactoryBuilder() {
}

//build方法
public SqlSessionFactory build(InputStream inputStream) {
return this.build((InputStream)inputStream, (String)null, (Properties)null);
}

//build方法(重载)
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
SqlSessionFactory var5;
try {
//第一步: 创建XML配置构建器,用来解析全局XML文件内容
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
var5 = this.build(parser.parse());
} catch (Exception var14) {
throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
} finally {
ErrorContext.instance().reset();
try {
inputStream.close();
} catch (IOException var13) {
}
}
return var5;
}

在继续深入之前我们需要了解一下

XMLConfigBuilder

XMLConfigBuilder

BaseBuilder

BaseBuilder

Configuration

Configuration

XMLMapperBuilder

XMLStatementBuilder

MapperBuilderAssistant

BaseBuilder

XMLxxxBuilder是用来解析XML配置文件的，不同类型XMLxxxBuilder用来解析MyBatis配置文件的不同部位。

• XMLConfigBuilder用来解析MyBatis的全局配置文件
• XMLMapperBuilder用来解析MyBatis中的映射文件
• XMLStatementBuilder用来解析映射文件中的statement语句。
• MapperBuilderAssistant用来辅助解析映射文件并生成MappedStatement对象

这些XMLxxxBuilder都有一个共同的父类——

BaseBuilder

Configuration

看源码果然能发现猫腻,不错不错,可以看到在

new

XMLConfigBuilder

super(new Configuration());

可以看到

Configuration

Configuration

public Configuration() {
this.safeResultHandlerEnabled = true;
this.multipleResultSetsEnabled = true;
this.useColumnLabel = true;
this.cacheEnabled = true;
this.useActualParamName = true;
this.localCacheScope = LocalCacheScope.SESSION;
this.jdbcTypeForNull = JdbcType.OTHER;
this.lazyLoadTriggerMethods = new HashSet(Arrays.asList("equals", "clone", "hashCode", "toString"));
this.defaultExecutorType = ExecutorType.SIMPLE;
this.autoMappingBehavior = AutoMappingBehavior.PARTIAL;
this.autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
this.variables = new Properties();
this.reflectorFactory = new DefaultReflectorFactory();
this.objectFactory = new DefaultObjectFactory();
this.objectWrapperFactory = new DefaultObjectWrapperFactory();
this.lazyLoadingEnabled = false;
this.proxyFactory = new JavassistProxyFactory();
this.mapperRegistry = new MapperRegistry(this);
this.interceptorChain = new InterceptorChain();
this.typeHandlerRegistry = new TypeHandlerRegistry();
this.typeAliasRegistry = new TypeAliasRegistry();
this.languageRegistry = new LanguageDriverRegistry();
this.mappedStatements = new Configuration.StrictMap("Mapped Statements collection");
this.caches = new Configuration.StrictMap("Caches collection");
this.resultMaps = new Configuration.StrictMap("Result Maps collection");
this.parameterMaps = new Configuration.StrictMap("Parameter Maps collection");
this.keyGenerators = new Configuration.StrictMap("Key Generators collection");
this.loadedResources = new HashSet();
this.sqlFragments = new Configuration.StrictMap("XML fragments parsed from previous mappers");
this.incompleteStatements = new LinkedList();
this.incompleteCacheRefs = new LinkedList();
this.incompleteResultMaps = new LinkedList();
this.incompleteMethods = new LinkedList();
this.cacheRefMap = new HashMap();
this.typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
this.typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
this.typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
this.typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
this.typeAliasRegistry.registerAlias("LRU", LruCache.class);
this.typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
this.typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
this.typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
this.typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
this.typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
this.typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
this.typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
this.typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
this.typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
this.typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
this.typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
this.typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
this.typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
this.typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
this.languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
this.languageRegistry.register(RawLanguageDriver.class);
}

第一步还没有执行完? 是的上述中我们在看构建

XMLConfigBuilder

parser.parse();

XMLConfigBuilder

public Configuration parse() {
//判断是否已经解析,只能解析一次全局配置文件
if (this.parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
} else {
//将parsed标记为已经解析
this.parsed = true;
//解析全局配置文件的XML中的configuration节点
this.parseConfiguration(this.parser.evalNode("/configuration"));
return this.configuration;
}
}

//主要看一下解析全局配置文件的configuration节点的方法
private void parseConfiguration(XNode root) {
try {
//解析全局配置文件中的properties节点的配置信息存储到Configuration对象的variables属性中
this.propertiesElement(root.evalNode("properties"));
//解析全局配置文件中的settings节点的配置信息设置到Configuration对象的各个属性中
Properties settings = this.settingsAsProperties(root.evalNode("settings"));
this.loadCustomVfs(settings);
this.settingsElement(settings);
//解析全局配置文件中的typeAliases节点的配置信息设置到BaseBuilder对象的TypeAliasRegistry属性中
this.typeAliasesElement(root.evalNode("typeAliases"));
//解析全局配置文件的plugins
this.pluginElement(root.evalNode("plugins"));
//解析全局配置文件中的objectFactory设置到Configuration对象的objectFactory属性中
this.objectFactoryElement(root.evalNode("objectFactory"));
this.objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
this.reflectorFactoryElement(root.evalNode("reflectorFactory"));
//解析全局配置文件中的Environment节点存储到Configuration对象中的Environment属性中

this.environmentsElement(root.evalNode("environments"));
this.databaseIdProviderElement(root.evalNode("databaseIdProvider"));
this.typeHandlerElement(root.evalNode("typeHandlers"));
//第二步 : 解析全局配置文件中的mappers节点  注意这是一个核心的方法 我们点进去看一下
this.mapperElement(root.evalNode("mappers"));
} catch (Exception var3) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + var3, var3);
}
}

从上述代码中可以看到，XMLConfigBuilder会依次解析配置文件中的、、、、、等属性。

第二步 : 解析映射配置文件XML到Configuration的mapperRegistry容器

this.mapperElement(root.evalNode("mappers"));

主要功能 : MyBatis会遍历下所有的子节点，如果当前遍历到的节点是，则MyBatis会将该包下的所有Mapper Class注册到configuration的mapperRegistry容器中。如果当前节点为，则会依次获取resource、url、class属性，解析映射文件，并将映射文件对应的Mapper Class注册到configuration的mapperRegistry容器中。

XMLConfigBuilder

this.mapperElement(root.evalNode("mappers"))

XMLMapperBuilder

XMLConfigBuilder

上图中红色圈中的是Mybatis解析映射文件的方法,我们进去看一下

mapperParser = new XMLMapperBuilder(inputStream, this.configuration, resource, this.configuration.getSqlFragments());

private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {
//首先会初始化父类BaseBuilder，并将configuration赋给BaseBuilder；
super(configuration);
//然后创建MapperBuilderAssistant对象，该对象为XMLMapperBuilder的协助者，用来协助XMLMapperBuilder完成一些解析映射文件的动作
this.builderAssistant = new MapperBuilderAssistant(configuration, resource);

this.parser = parser;
this.sqlFragments = sqlFragments;
this.resource = resource;
}

public void parse() {
if (!this.configuration.isResourceLoaded(this.resource)) {
this.configurationElement(this.parser.evalNode("/mapper"));
this.configuration.addLoadedResource(this.resource);
this.bindMapperForNamespace();
}

this.parsePendingResultMaps();
this.parsePendingCacheRefs();
this.parsePendingStatements();
}

再看一下

mapperParser.parse();

public void parse() {
//如果映射文件没有被加载过
if (!this.configuration.isResourceLoaded(this.resource)) {
//执行加载映射文件XML方法configurationElement
this.configurationElement(this.parser.evalNode("/mapper"));
//将此映射文件添加已经解析了的集合中
this.configuration.addLoadedResource(this.resource);
//绑定Namespace
this.bindMapperForNamespace();
}

this.parsePendingResultMaps();
this.parsePendingCacheRefs();
this.parsePendingStatements();
}

下面是具体Mybatis解析映射文件中的Statement的过程

private void configurationElement(XNode context) {
try {
//获取namespace
String namespace = context.getStringAttribute("namespace");
//判断namespace,如果为空直接抛出异常
if (namespace != null && !namespace.equals("")) {
//设置namespace
this.builderAssistant.setCurrentNamespace(namespace);
//下面就是解析各个Statement中的各个XML节点
this.cacheRefElement(context.evalNode("cache-ref"));
this.cacheElement(context.evalNode("cache"));
this.parameterMapElement(context.evalNodes("/mapper/parameterMap"));
this.resultMapElements(context.evalNodes("/mapper/resultMap"));
this.sqlElement(context.evalNodes("/mapper/sql"));

//第三步 : 解析Statement声明   核心方法
this.buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
} else {
throw new BuilderException("Mapper's namespace cannot be empty");
}
} catch (Exception var3) {
throw new BuilderException("Error parsing Mapper XML. Cause: " + var3, var3);
}
}

从上述代码中可以看到，

XMLMapperBuilder

MapperBuilderAssistant

MappedStatement

第三步 : 解析映射文件的Statement为MappedStatement对象

主要功能 : 将映射文件的子节点解析为

MappedStatement

我们进入

this.buildStatementFromContext(context.evalNodes("select|insert|update|delete"));

private void buildStatementFromContext(List<XNode> list) {
if (this.configuration.getDatabaseId() != null) {
this.buildStatementFromContext(list, this.configuration.getDatabaseId());
}

this.buildStatementFromContext(list, (String)null);
}

private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
Iterator var3 = list.iterator();

while(var3.hasNext()) {
XNode context = (XNode)var3.next();
XMLStatementBuilder statementParser = new XMLStatementBuilder(this.configuration, this.builderAssistant, context, requiredDatabaseId);

try {
statementParser.parseStatementNode();
} catch (IncompleteElementException var7) {
this.configuration.addIncompleteStatement(statementParser);
}
}

}

其中主要的逻辑都在下示图中的两行代码中

接下来我们进入XMLStatementBuilder类的

parseStatementNode

最终由

MapperBuilderAssistant

MappedStatement

MappedStatement

Configuration

mappedStatements

初始化完成

主要功能 : 将已经装载了各种XML信息的Configuration对象作为参数构建DefaultSqlSessionFactory返回,Mybatis初始化完成!!!

public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}