源码版本
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.4</version>
</dependency>
阅读入口
@Before
public void prepare() throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}
源码走读
首先进入sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);此处主要是对mybatis-config.xml解析。
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
try {
// 用于解析 mybatis-config.xml，同时创建了 Configuration 对象 >> 此处使用了构造者模式
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
// 解析XML，最终返回一个 DefaultSqlSessionFactory >>
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.
}
}
}
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
super(new Configuration());
ErrorContext.instance().resource("SQL Mapper Configuration");
this.configuration.setVariables(props);
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
public Configuration() {
// 为类型注册别名
typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
typeAliasRegistry.registerAlias("LRU", LruCache.class);
typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
languageRegistry.register(RawLanguageDriver.class);
}
到此XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);已经解析完毕，返回了包含Configuration的XMLConfigBuilder对象。
此时类图结构如下所示:
configuration类图.jpg
接下来进行配置的解析：parser.parse();
public Configuration parse() {
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
// XPathParser，dom 和 SAX 都有用到 >>
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
解析的文件是mybatis的配置文件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>
<properties resource="db.properties"></properties>
<settings>
<!-- 打印查询语句 -->
<setting name="logImpl" value="STDOUT_LOGGING" />
<!-- 控制全局缓存（二级缓存），默认 true-->
<setting name="cacheEnabled" value="true"/>
<!-- 延迟加载的全局开关。当开启时，所有关联对象都会延迟加载。默认 false -->
<setting name="lazyLoadingEnabled" value="true"/>
<!-- 当开启时，任何方法的调用都会加载该对象的所有属性。默认 false，可通过select标签的 fetchType来覆盖-->
<setting name="aggressiveLazyLoading" value="true"/>
<!-- Mybatis 创建具有延迟加载能力的对象所用到的代理工具，默认JAVASSIST -->
<!--<setting name="proxyFactory" value="CGLIB" />-->
<!-- STATEMENT级别的缓存，使一级缓存，只针对当前执行的这一statement有效 -->
<!--
<setting name="localCacheScope" value="STATEMENT"/>
-->
<setting name="localCacheScope" value="SESSION"/>
</settings>
<typeAliases>
<typeAlias alias="blog" type="com.zifeng.domain.Blog" />
<typeAlias type="com.zifeng.domain.BlogCheckBox" alias="checkBox"/>
</typeAliases>
<!-- <typeHandlers>
<typeHandler handler="com.zifeng.type.MyTypeHandler"></typeHandler>
</typeHandlers>-->
<!-- 对象工厂 -->
<!-- <objectFactory type="com.zifeng.objectfactory.ZFObjectFactory">
<property name="zifeng" value="666"/>
</objectFactory>-->
<!-- <plugins>
<plugin interceptor="com.zifeng.interceptor.SQLInterceptor">
<property name="zifeng" value="betterme" />
</plugin>
<plugin interceptor="com.zifeng.interceptor.MyPageInterceptor">
</plugin>
</plugins>-->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/><!-- 单独使用时配置成MANAGED没有事务 -->
<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 resource="BlogMapper.xml"/>
<mapper resource="BlogMapperExt.xml"/>
</mappers>
</configuration>
解析时，先获取<configuration>的node节点，接下来，以这个父节点为基础，解析其子节点及子节点的属性，最后填充到Configuration对象中。
private void parseConfiguration(XNode root) {
try {
//issue #117 read properties first
// 对于全局配置文件各种标签的解析
propertiesElement(root.evalNode("properties"));
// 解析 settings 标签
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
// 类型别名
typeAliasesElement(root.evalNode("typeAliases"));
// 插件
pluginElement(root.evalNode("plugins"));
// 用于创建对象
objectFactoryElement(root.evalNode("objectFactory"));
// 用于对对象进行加工
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
// 反射工具箱
reflectorFactoryElement(root.evalNode("reflectorFactory"));
// settings 子标签赋值，默认值就是在这里提供的 >>
settingsElement(settings);
// read it after objectFactory and objectWrapperFactory issue #631
// 创建了数据源 >>
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
// 解析引用的Mapper映射器
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
其中有两个比较重要的解析，一个时plugins插件，一个是mappers即mapper映射器。
private void pluginElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
String interceptor = child.getStringAttribute("interceptor");
Properties properties = child.getChildrenAsProperties();
Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).getDeclaredConstructor().newInstance();
interceptorInstance.setProperties(properties);
configuration.addInterceptor(interceptorInstance);
}
}
}
public void addInterceptor(Interceptor interceptor) {
interceptorChain.addInterceptor(interceptor);
}
public class InterceptorChain {
private final List<Interceptor> interceptors = new ArrayList<>();
public Object pluginAll(Object target) {
for (Interceptor interceptor : interceptors) {
target = interceptor.plugin(target);
}
return target;
}
public void addInterceptor(Interceptor interceptor) {
interceptors.add(interceptor);
}
public List<Interceptor> getInterceptors() {
return Collections.unmodifiableList(interceptors);
}
}
plugins解析完毕以后放置在Configuration的InterceptorChain的插件链中。
接下来是mapper映射器的解析。
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
// 不同的定义方式的扫描，最终都是调用 addMapper()方法（添加到 MapperRegistry）。这个方法和 getMapper() 对应
// package 包
if ("package".equals(child.getName())) {
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
if (resource != null && url == null && mapperClass == null) {
// resource 相对路径
ErrorContext.instance().resource(resource);
InputStream inputStream = Resources.getResourceAsStream(resource);
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
// 解析 Mapper.xml，总体上做了两件事情 >>
mapperParser.parse();
} else if (resource == null && url != null && mapperClass == null) {
// url 绝对路径
ErrorContext.instance().resource(url);
InputStream inputStream = Resources.getUrlAsStream(url);
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url == null && mapperClass != null) {
// class 单个接口
Class<?> mapperInterface = Resources.classForName(mapperClass);
configuration.addMapper(mapperInterface);
} else {
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}
//mapperParser.parse()
public void parse() {
// 总体上做了两件事情，对于语句的注册和接口的注册
if (!configuration.isResourceLoaded(resource)) {
// 1、具体增删改查标签的解析。
// 一个标签一个MappedStatement。 >>
configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
// 2、把namespace（接口类型）和工厂类绑定起来，放到一个map。
// 一个namespace 一个 MapperProxyFactory >>
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();
}
private void configurationElement(XNode context) {
try {
String namespace = context.getStringAttribute("namespace");
if (namespace == null || namespace.equals("")) {
throw new BuilderException("Mapper's namespace cannot be empty");
}
builderAssistant.setCurrentNamespace(namespace);
// 添加缓存对象
cacheRefElement(context.evalNode("cache-ref"));
// 解析 cache 属性，添加缓存对象
cacheElement(context.evalNode("cache"));
// 创建 ParameterMapping 对象
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
// 创建 List<ResultMapping>
resultMapElements(context.evalNodes("/mapper/resultMap"));
// 解析可以复用的SQL
sqlElement(context.evalNodes("/mapper/sql"));
// 解析增删改查标签，得到 MappedStatement >>
buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
} catch (Exception e) {
throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
}
}
private void buildStatementFromContext(List<XNode> list) {
if (configuration.getDatabaseId() != null) {
buildStatementFromContext(list, configuration.getDatabaseId());
}
// 解析 Statement >>
buildStatementFromContext(list, null);
}
private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
for (XNode context : list) {
// 用来解析增删改查标签的 XMLStatementBuilder
final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
try {
// 解析 Statement，添加 MappedStatement 对象 >>
statementParser.parseStatementNode();
} catch (IncompleteElementException e) {
configuration.addIncompleteStatement(statementParser);
}
}
}
public void parseStatementNode() {
String id = context.getStringAttribute("id");
String databaseId = context.getStringAttribute("databaseId");
if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
return;
}
String nodeName = context.getNode().getNodeName();
SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
boolean useCache = context.getBooleanAttribute("useCache", isSelect);
boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);
// Include Fragments before parsing
XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
includeParser.applyIncludes(context.getNode());
String parameterType = context.getStringAttribute("parameterType");
Class<?> parameterTypeClass = resolveClass(parameterType);
String lang = context.getStringAttribute("lang");
LanguageDriver langDriver = getLanguageDriver(lang);
// Parse selectKey after includes and remove them.
processSelectKeyNodes(id, parameterTypeClass, langDriver);
// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
KeyGenerator keyGenerator;
String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
if (configuration.hasKeyGenerator(keyStatementId)) {
keyGenerator = configuration.getKeyGenerator(keyStatementId);
} else {
keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
}
SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
Integer fetchSize = context.getIntAttribute("fetchSize");
Integer timeout = context.getIntAttribute("timeout");
String parameterMap = context.getStringAttribute("parameterMap");
String resultType = context.getStringAttribute("resultType");
Class<?> resultTypeClass = resolveClass(resultType);
String resultMap = context.getStringAttribute("resultMap");
String resultSetType = context.getStringAttribute("resultSetType");
ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
if (resultSetTypeEnum == null) {
resultSetTypeEnum = configuration.getDefaultResultSetType();
}
String keyProperty = context.getStringAttribute("keyProperty");
String keyColumn = context.getStringAttribute("keyColumn");
String resultSets = context.getStringAttribute("resultSets");
// >> 关键的一步： MappedStatement 的创建
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}
public MappedStatement addMappedStatement(
String id,
SqlSource sqlSource,
StatementType statementType,
SqlCommandType sqlCommandType,
Integer fetchSize,
Integer timeout,
String parameterMap,
Class<?> parameterType,
String resultMap,
Class<?> resultType,
ResultSetType resultSetType,
boolean flushCache,
boolean useCache,
boolean resultOrdered,
KeyGenerator keyGenerator,
String keyProperty,
String keyColumn,
String databaseId,
LanguageDriver lang,
String resultSets) {
if (unresolvedCacheRef) {
throw new IncompleteElementException("Cache-ref not yet resolved");
}
id = applyCurrentNamespace(id, false);
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType)
.resource(resource)
.fetchSize(fetchSize)
.timeout(timeout)
.statementType(statementType)
.keyGenerator(keyGenerator)
.keyProperty(keyProperty)
.keyColumn(keyColumn)
.databaseId(databaseId)
.lang(lang)
.resultOrdered(resultOrdered)
.resultSets(resultSets)
.resultMaps(getStatementResultMaps(resultMap, resultType, id))
.resultSetType(resultSetType)
.flushCacheRequired(valueOrDefault(flushCache, !isSelect))
.useCache(valueOrDefault(useCache, isSelect))
.cache(currentCache);
ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);
if (statementParameterMap != null) {
statementBuilder.parameterMap(statementParameterMap);
}
MappedStatement statement = statementBuilder.build();
// 最关键的一步，在 Configuration 添加了 MappedStatement >>
configuration.addMappedStatement(statement);
return statement;
}
当执行玩 configurationElement(parser.evalNode("/mapper"))此时Configuration中配置信息已经基本全部加载，然后开始设置mapper.java，bindMapperForNamespace()；
private void bindMapperForNamespace() {
String namespace = builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class<?> boundType = null;
try {
boundType = Resources.classForName(namespace);
} catch (ClassNotFoundException e) {
//ignore, bound type is not required
}
if (boundType != null) {
if (!configuration.hasMapper(boundType)) {
// Spring may not know the real resource name so we set a flag
// to prevent loading again this resource from the mapper interface
// look at MapperAnnotationBuilder#loadXmlResource
configuration.addLoadedResource("namespace:" + namespace);
// 添加到 MapperRegistry，本质是一个 map，里面也有 Configuration >>
configuration.addMapper(boundType);
}
}
}
}
public <T> void addMapper(Class<T> type) {
mapperRegistry.addMapper(type);
}
public <T> void addMapper(Class<T> type) {
if (type.isInterface()) {
if (hasMapper(type)) {
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
// ！Map<Class<?>, MapperProxyFactory<?>> 存放的是接口类型，和对应的工厂类的关系
knownMappers.put(type, new MapperProxyFactory<>(type));
// It's important that the type is added before the parser is run
// otherwise the binding may automatically be attempted by the
// mapper parser. If the type is already known, it won't try.
// 注册了接口之后，根据接口，开始解析所有方法上的注解，例如 @Select >>
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
解析结束，最后返回一个DefaultSqlSessionFactory；至此配置解析完毕，下一回就开始进行数据操作。
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
注：本文源码注释来自于咕泡-青山老师
