Mybatis系列一:构建SqlSessionFactory
一、SqlSessionFactoryBuilder
SqlSessionFactoryBuilder的build方法接受Reader/InputStream/Configuration作为配置源,创建SqlSessionFactory实例。在接受Reader/InputStream作为配置源时,创建了XMLConfigBuilder实例来解析XML配置。
public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
try {
XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
reader.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
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.
}
}
}
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
二、XMLConfigBuilder
2.1 类图
2.2 解析Mybatis配置 parse
settings、mappers元素的解析稍微复杂些。
public Configuration parse() {
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
2.3 解析configuration元素 parseConfiguration
Mybatis配置文件解析流水线式按部就班的解析,各元素解析逻辑分散到独立方法中,清晰了然。
private void parseConfiguration(XNode root) {
try {
// 解析properties元素并设置到Configuration对象
propertiesElement(root.evalNode("properties"));
// 解析settings元素保存到Properties中
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
// 解析typeAliases元素并设置到Configuration对象
typeAliasesElement(root.evalNode("typeAliases"));
// 解析plugins元素并设置到Configuration对象
pluginElement(root.evalNode("plugins"));
// 解析objectFactory元素并设置到Configuration对象
objectFactoryElement(root.evalNode("objectFactory"));
// 解析objectWrapperFactory元素并设置到Configuration对象
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
// 解析reflectorFactory元素并设置到Configuration对象
reflectorFactoryElement(root.evalNode("reflectorFactory"));
// settings配置值保存到Configuration对象
settingsElement(settings);
// 解析environments元素默认environment并设置到Configuration对象
environmentsElement(root.evalNode("environments"));
// 解析databaseIdProvider元素并设置到Configuration对象
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
// 解析typeHandlers元素并设置到Configuration对象
typeHandlerElement(root.evalNode("typeHandlers"));
// 解析mappers元素并设置到Configuration对象
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
2.4 解析properties元素
<properties resource="jdbc.properties">
<property name="jdbc.username" value="username"/>
<property name="hello" value="hello"/>
</properties>
2.4.1 解析流程
(1) 解析properties子元素保存到Properties中
(2) 获取properties的resource或url属性值指定的外部配置,设置到(1)中,同名覆盖
(3) 创建XMLConfigBuilder或SqlSessionFactory实例时如果指定了Properties,设置到(1)中,同名覆盖
存在这样一个优先级顺序:properties子元素 < properties的resource或url属性 < 参数Properties
2.4.2 propertiesElement
private void propertiesElement(XNode context) throws Exception {
if (context != null) {
// 获取properties子元素保存到Properties中
Properties defaults = context.getChildrenAsProperties();
// properties的resource、url属性值
String resource = context.getStringAttribute("resource");
String url = context.getStringAttribute("url");
// properties的resource、url属性不能同时配置
if (resource != null && url != null) {
throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference. Please specify one or the other.");
}
// 根据properties的resource、url属性值获取外部配置,保存到defaults中,同名属性会覆盖
if (resource != null) {
defaults.putAll(Resources.getResourceAsProperties(resource));
} else if (url != null) {
defaults.putAll(Resources.getUrlAsProperties(url));
}
// 创建XMLConfigBuilder或SqlSessionFactory实例时如果指定了Properties,设置到Configuration的variables属性上
Properties vars = configuration.getVariables();
if (vars != null) {
defaults.putAll(vars);
}
parser.setVariables(defaults);
configuration.setVariables(defaults);
}
}
2.5 解析settings元素
<settings>
<setting name="cacheEnabled" value="true"/>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="autoMappingBehavior" value="PARTIAL"/>
</settings>
2.5.1 解析流程
(1) 获取settings子元素保存到Properties中
(2) 获取Configuration类的所有属性、getter和setter方法
(3) 检查setting(name属性值)在Configuration类中是否存在,不存在抛异常
2.5.2 settingsAsProperties
private Properties settingsAsProperties(XNode context) {
if (context == null) {
return new Properties();
}
// 获取settings子元素保存到Properties中
Properties props = context.getChildrenAsProperties();
// 检查配置类是否知道所有设置,MetaClass后续分析。传送门《Mybatis系列二:MetaClass解析Configuration元数据》
MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);
for (Object key : props.keySet()) {
// 配置的setting(name属性值)不是Configuration的属性,则抛出异常
if (!metaConfig.hasSetter(String.valueOf(key))) {
throw new BuilderException("The setting " + key + " is not known. Make sure you spelled it correctly (case sensitive).");
}
}
return props;
}
2.6 解析typeAliases元素
配置包名,让MyBatis去扫描包中的类,并根据类名得到相应的别名。可配合@Alias注解使用,不让MyBatis按照默认规则生成别名。传送门《Mybatis系列三:类型别名、类型解析器的注册》
<typeAliases>
<package name="com.lemon.entity"/>
<package name="com.lemon.service/>
</typeAliases>
明确为某个类配置别名
<typeAliases>
<typeAlias type="com.lemon.entity.Movie" />
<typeAlias alias="author" type="com.lemon.entity.Ideal" />
</typeAliases>
2.6.1 解析流程
(1) package子元素:扫描指定包下的类,可结合@Alias注解指定别名,或者按默认规则生成别名
(2) typeAlias子元素:按照配置为类设置别名,未指定按默认规则生成别名
2.6.2 typeAliasesElement
private void typeAliasesElement(XNode parent) {
if (parent != null) {
for (XNode child : parent.getChildren()) {
// 扫描指定包下的类,可结合@Alias注解指定别名,或者按默认规则生成别名
if ("package".equals(child.getName())) {
String typeAliasPackage = child.getStringAttribute("name");
configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
} else {
// 明确为某个类配置别名
String alias = child.getStringAttribute("alias");
String type = child.getStringAttribute("type");
try {
Class<?> clazz = Resources.classForName(type);
if (alias == null) {
typeAliasRegistry.registerAlias(clazz);
} else {
typeAliasRegistry.registerAlias(alias, clazz);
}
} catch (ClassNotFoundException e) {
throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
}
}
}
}
}
2.7 解析plugins元素
2.7.1 plugin介绍
通过插件机制我们可在SQL执行过程中的某些点上做一些自定义操作。实现一个插件首先需要让插件类实现 Interceptor接口,然后在插件类上添加@Intercepts 和@Signature 注解,用于指定想要拦截的目标方法。 MyBatis 允许拦截下面接口中的一些方法:
Executor: update, query, flushStatements, commit, rollback, getTransaction,close, isClosed
ParameterHandler: getParameterObject, setParameters
StatementHandler: prepare, parameterize, batch, update, query
ResultSetHandler: handleResultSets, handleOutputParameters
<plugins>
<plugin interceptor="com.lemon.plugin.ExamplePlugin">
<property name="key" value="value"/>
</plugin>
</plugins>
2.7.2 解析流程
(1) 获取interceptor的子元素保存到Properties中
(2) 实例化interceptor并设置属性(1)
2.7.3 pluginElement
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).newInstance();
interceptorInstance.setProperties(properties);
configuration.addInterceptor(interceptorInstance);
}
}
}
2.8 解析objectFactory元素
private void objectFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
Properties properties = context.getChildrenAsProperties();
ObjectFactory factory = (ObjectFactory) resolveClass(type).newInstance();
factory.setProperties(properties);
configuration.setObjectFactory(factory);
}
}
2.9 解析objectWrapperFactory元素
private void objectWrapperFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).newInstance();
configuration.setObjectWrapperFactory(factory);
}
}
2.10 解析reflectorFactory元素
private void reflectorFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
ReflectorFactory factory = (ReflectorFactory) resolveClass(type).newInstance();
configuration.setReflectorFactory(factory);
}
}
2.11 解析environments元素
private void environmentsElement(XNode context) throws Exception {
if (context != null) {
// 创建XMLConfigBuilder或SqlSessionFactory实例时没有指定environment,获取默认environment
if (environment == null) {
environment = context.getStringAttribute("default");
}
for (XNode child : context.getChildren()) {
String id = child.getStringAttribute("id");
// 判断是不是指定的Environment
if (isSpecifiedEnvironment(id)) {
// 获取事务工厂 JDBC/MANAGED
TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
// 获取数据源工厂 JNDI/POOLED/UNPOOLED
DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
DataSource dataSource = dsFactory.getDataSource();
// 根据数据源和事务构建Environment
Environment.Builder environmentBuilder = new Environment.Builder(id)
.transactionFactory(txFactory)
.dataSource(dataSource);
configuration.setEnvironment(environmentBuilder.build());
}
}
}
}
2.12 解析databaseIdProvider元素
2.4.1 解析流程
2.4.2 propertiesElement
// 默认注册了类别名DB_VENDOR --> VendorDatabaseIdProvider
private void databaseIdProviderElement(XNode context) throws Exception {
DatabaseIdProvider databaseIdProvider = null;
if (context != null) {
String type = context.getStringAttribute("type");
// awful patch to keep backward compatibility
if ("VENDOR".equals(type)) {
type = "DB_VENDOR";
}
Properties properties = context.getChildrenAsProperties();
databaseIdProvider = (DatabaseIdProvider) resolveClass(type).newInstance();
databaseIdProvider.setProperties(properties);
}
Environment environment = configuration.getEnvironment();
if (environment != null && databaseIdProvider != null) {
// 获取元数据得到数据库标识
String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
configuration.setDatabaseId(databaseId);
}
}
2.13 解析typeHandlers元素
<!-- 自动扫描 -->
<typeHandlers>
<package name="com.lemon.handlers"/>
</typeHandlers>
<!-- 手动配置 -->
<typeHandlers>
<typeHandler jdbcType="TINYINT"
javaType="com.lemon.handlers.Movie"
handler="com.lemon.handlers.MovieTypeHandler"/>
</typeHandlers>
private void typeHandlerElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
String typeHandlerPackage = child.getStringAttribute("name");
typeHandlerRegistry.register(typeHandlerPackage);
} else {
String javaTypeName = child.getStringAttribute("javaType");
String jdbcTypeName = child.getStringAttribute("jdbcType");
String handlerTypeName = child.getStringAttribute("handler");
Class<?> javaTypeClass = resolveClass(javaTypeName);
JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
Class<?> typeHandlerClass = resolveClass(handlerTypeName);
// 如果未配置javaType、jdbcType,获取TypeHandler类上@MappedTypes、@MappedJdbcTypes注解
if (javaTypeClass != null) {
if (jdbcType == null) {
typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
} else {
typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
}
} else {
typeHandlerRegistry.register(typeHandlerClass);
}
}
}
}
}
2.14 解析mappers元素
<mappers>
<mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
<mapper url="file:///var/mappers/AuthorMapper.xml"/>
<mapper class="org.mybatis.builder.AuthorMapper"/>
<package name="org.mybatis.builder"/>
</mappers>
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
// 扫描指定包下的Mapper
String mapperPackage = child.getStringAttribute("name");
// 传送门《Mybatis系列五:MapperAnnotationBuilder解析Mapper Class》
configuration.addMappers(mapperPackage);
} else {
// 获取resource、url、class属性,只能设置其中一个否则抛异常
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
if (resource != null && url == null && mapperClass == null) {
ErrorContext.instance().resource(resource);
InputStream inputStream = Resources.getResourceAsStream(resource);
// 传送门《Mybatis系列四:XMLMapperBuilder解析XL配置文件》
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url != null && mapperClass == null) {
ErrorContext.instance().resource(url);
InputStream inputStream = Resources.getUrlAsStream(url);
// 传送门《Mybatis系列四:XMLMapperBuilder解析XL配置文件》
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url == null && mapperClass != null) {
Class<?> mapperInterface = Resources.classForName(mapperClass);
// 获取Mapper注册到Configuration的MapperRegistry属性中
// 传送门《Mybatis系列五:MapperAnnotationBuilder解析Mapper Class》
configuration.addMapper(mapperInterface);
} else {
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}