介绍：MyBatis是一流的持久性框架，支持自定义SQL，存储过程和高级映射。MyBatis消除了几乎所有的JDBC代码以及参数的手动设置和结果检索。MyBatis可以使用简单的XML或注释进行配置，并将映射接口和Java POJO（普通的旧Java对象）映射到数据库记录。
开始看源码：
public static void main(String[] args) throws IOException {
// 加载配置文件
InputStream inputStream = Resources.getResourceAsStream("config.xml");
// 解析配置文件构建SqlsessionFactory，本篇文章就是从这个地方开始展开。//只看这一句话
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 创建 defaultSqlSession 对象
SqlSession session = sqlSessionFactory.openSession();
// 执行查询
UserMapper mapper = session.getMapper(UserMapper.class);
LogLogin logLogin = mapper.selectByPrimaryKey(1);
System.out.println(logLogin.toString());
}
// 根据配置文件的输入流，构建配置类对象
public SqlSessionFactory build(InputStream inputStream) {
return build(inputStream, null, null); // 继续跟进
}
// 和主要逻辑没有关系的代码先删掉了。减少干扰
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
try {
// 解析xml文件，转换成XMLConfigBuilder对象，不展开了，就是解析xml文件
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
// ★ parser.parse() 解析加载Mybatis相关的XML配置文件 mapper 连接信息等
// build 构建SqlSessionFactory
return build(parser.parse()); // 这俩方法展开看一下
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession .", e);
} finally {
ErrorContext.instance().reset();
// 关闭流代码省略
}
}
/** 解析配置文件 */
// 标识是否解析过配置文件
private boolean parsed;
public Configuration parse() {
// 确保文件只能解析一次
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true; // 解析一次之后，改为true
// 真正解析配置文件，赋值给配置类 Configuration,该类是MyBatis的主要配置文件类
// parser.evalNode("/configuration") 解析configuration节点
parseConfiguration(parser.evalNode("/configuration")); // 下面来看parseConfiguration()
return configuration;
}
/**
* 真正解析配置文件，赋值给配置类Configuration
* 获取xml的节点属性，存入配置类, 数据库连接，用户名 密码 mapper 关系映射等等
*/
private void parseConfiguration(XNode root) {
try {
// 解析 properties 节点
propertiesElement(root.evalNode("properties"));
// 解析 settings 节点
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
// 解析 typeAliases 节点
typeAliasesElement(root.evalNode("typeAliases"));
// 解析 plugins 节点
pluginElement(root.evalNode("plugins"));
// 解析 objectFactory 节点
objectFactoryElement(root.evalNode("objectFactory"));
// 解析 objectWrapperFactory 节点
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
// 解析 reflectorFactory 节点
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// ★ 数据库类型 帐号密码 配置 可参照下图看一下👇
environmentsElement(root.evalNode("environments"));
// 解析 databaseIdProvider 节点
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
// 解析 typeHandlers 节点
typeHandlerElement(root.evalNode("typeHandlers"));
// ★ xml sql语句加载 可参照下图看一下👇
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
下面是把配置信息载入Configuration的每个节点的相关逻辑
第一步：解析properties节点: propertiesElement(root.evalNode("properties"));
带着这段xml看会好一些
<properties resource="org/mybatis/example/config.properties">
<property name="username" value="dev_user"/>
<property name="password" value="F2Fa3!33TYyg"/>
</properties>
private void propertiesElement(XNode context) throws Exception {
if (context != null) {
// 获取子dom
Properties defaults = context.getChildrenAsProperties();
// 获取properties的 resource & url 俩兄弟属性不能同时存在
String resource = context.getStringAttribute("resource");
String url = context.getStringAttribute("url");
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.");
}
// 俩兄弟谁在都行 Properties其实底层就是个HashTable，putAll()就是hashtable的方法
if (resource != null) {
defaults.putAll(Resources.getResourceAsProperties(resource));
} else if (url != null) {
defaults.putAll(Resources.getUrlAsProperties(url));
}
// configuration.getVariables()返回一个Properties 的对象，variables是Configuration的一个属性
// 很多配置文件都是存在这个属性里的，这里判断下，之前存过属性的话，就需要合并一下
Properties vars = configuration.getVariables();
if (vars != null) {
defaults.putAll(vars);
}
// 更新Variables字段
parser.setVariables(defaults);
// 重新赋值。
configuration.setVariables(defaults);
}
}
第二步：解析 settings 节点
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
xml示例
<settings>
<setting name="cacheEnabled" value="true"/>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="multipleResultSetsEnabled" value="true"/>
<setting name="useColumnLabel" value="true"/>
.....
</settings>
// 虚拟文件系统 用来查找指定路径 下的资源
private void loadCustomVfs(Properties props) throws ClassNotFoundException {
String value = props.getProperty("vfsImpl");
if (value != null) {
String[] clazzes = value.split(",");
for (String clazz : clazzes) {
if (!clazz.isEmpty()) {
@SuppressWarnings("unchecked")
Class<? extends VFS> vfsImpl = (Class<? extends VFS>)Resources.classForName(clazz);
configuration.setVfsImpl(vfsImpl);
}
}
}
}
// 加载自定义 LogImpl
private void loadCustomLogImpl(Properties props) {
Class<? extends Log> logImpl = resolveClass(props.getProperty("logImpl"));
configuration.setLogImpl(logImpl);
}
第三步：解析 typeAliases 节点 typeAliasesElement(root.evalNode("typeAliases"));
typeAliases 的 xml示例:
1
<typeAliases>
<typeAlias alias="Author" type="domain.blog.Author"/>
<typeAlias alias="Blog" type="domain.blog.Blog"/>
.....
</typeAliases>
2
<typeAliases>
<package name="domain.blog"/>
</typeAliases>
// 没啥可说的了 ，大同小异
private void typeAliasesElement(XNode parent) {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
String typeAliasPackage = child.getStringAttribute("name");
configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
} else {
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);
}
}
}
}
}
第三步：解析 plugins 节点 pluginElement(root.evalNode("plugins"));
这里挺重要的。 sql的拦截器都是通过这个来进行实现的，后面会说到执行。
plugins 的 xml示例: 配置自定义插件
<plugins>
<plugin interceptor="org.mybatis.example.ExamplePlugin">
<property name="someProperty" value="100"/> -- 传的参数，插件中可以获取到
</plugin>
</plugins>
private void pluginElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
// 获取插件对象全路径
String interceptor = child.getStringAttribute("interceptor");
// 获取参数
Properties properties = child.getChildrenAsProperties();
// 通过反射创建插件（Mybatis的拦截器）实例对象
Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).getDeclaredConstructor().newInstance();
// 设置参数
interceptorInstance.setProperties(properties);
// 把拦截器加入主配置对象里面
configuration.addInterceptor(interceptorInstance);
}
}
}
第四步：解析objectFactory节点 objectFactoryElement(root.evalNode("objectFactory"));
objectFactory的xml示例
<objectFactory type="org.mybatis.example.ExampleObjectFactory">
<property name="someProperty" value="100"/>
</objectFactory>
// 先获取工厂类，通过反射创建实例，赋值放入主配置文件 和上面的插件加载逻辑一样，换个名字。
private void objectFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
Properties properties = context.getChildrenAsProperties();
ObjectFactory factory = (ObjectFactory) resolveClass(type).getDeclaredConstructor().newInstance();
factory.setProperties(properties);
configuration.setObjectFactory(factory);
}
}
第五步：解析 objectWrapperFactory 节点 objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
// 还是一样的逻辑 和ObjectFactory一样
private void objectWrapperFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
ObjectWrapperFactory factory = (ObjectWrapperFactory) resolveClass(type).getDeclaredConstructor().newInstance();
configuration.setObjectWrapperFactory(factory);
}
}
第六步：解析 reflectorFactory 节点 reflectorFactoryElement(root.evalNode("reflectorFactory"));
// 又来一个。。。
private void reflectorFactoryElement(XNode context) throws Exception {
if (context != null) {
String type = context.getStringAttribute("type");
ReflectorFactory factory = (ReflectorFactory) resolveClass(type).getDeclaredConstructor().newInstance();
configuration.setReflectorFactory(factory);
}
}
第七步： 一大堆配置来袭
private void settingsElement(Properties props) {
configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));
configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));
configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));
configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));
configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), false));
configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));
configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));
configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));
configuration.setDefaultFetchSize(integerValueOf(props.getProperty("defaultFetchSize"), null));
configuration.setDefaultResultSetType(resolveResultSetType(props.getProperty("defaultResultSetType")));
configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));
configuration.setDefaultEnumTypeHandler(resolveClass(props.getProperty("defaultEnumTypeHandler")));
configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));
configuration.setUseActualParamName(booleanValueOf(props.getProperty("useActualParamName"), true));
configuration.setReturnInstanceForEmptyRow(booleanValueOf(props.getProperty("returnInstanceForEmptyRow"), false));
configuration.setLogPrefix(props.getProperty("logPrefix"));
configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
}
第八步： 解析 environments 节点 environmentsElement(root.evalNode("environments"));
这个是大家都熟悉的东西了, >用户名 密码 数据库连接等
environments 的xml 示例
<environments default="development">
<environment id="development">
<transactionManager type="JDBC">
<property name="..." value="..."/>
</transactionManager>
<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>
// 数据库类型、连接信息 帐号密码配置
private void environmentsElement(XNode context) throws Exception {
if (context != null) {
if (environment == null) {
// 根据default设置的属性值，选取加载environment id为属性值的那一个配置
environment = context.getStringAttribute("default");
}
for (XNode child : context.getChildren()) {
String id = child.getStringAttribute("id");
// 判断需要加载的配置 通过environment判断，这个是XMLConfigBuilder中的属性，string类型，不是主配置configuration中的
if (isSpecifiedEnvironment(id)) {
// 事务工厂
TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
// 数据源工厂对象
DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
// 数据源对象
DataSource dataSource = dsFactory.getDataSource();
// 这里是主配置中的Environment了 👇 下面简单了解下这个类属性
Environment.Builder environmentBuilder = new Environment.Builder(id)
.transactionFactory(txFactory)
.dataSource(dataSource);
configuration.setEnvironment(environmentBuilder.build());
}
}
}
}
public final class Environment { // 存储环境信息的类
private final String id;
private final TransactionFactory transactionFactory;
private final DataSource dataSource;
}
第九步：解析 databaseIdProvider 节点
xml 示例
<databaseIdProvider type="DB_VENDOR">
<property name="SQL Server" value="sqlserver"/>
<property name="DB2" value="db2"/>
<property name="Oracle" value="oracle" />
</databaseIdProvider>
// 选择使用的数据库
private void databaseIdProviderElement(XNode context) throws Exception {
DatabaseIdProvider databaseIdProvider = null;
if (context != null) {
String type = context.getStringAttribute("type");
// 为了版本兼容 myabtis这里做了兼容处理， 很像我写的代码。-_-
if ("VENDOR".equals(type)) {
type = "DB_VENDOR";
}
// 获取属性，反射创建DatabaseIdProvider对象
Properties properties = context.getChildrenAsProperties();
databaseIdProvider = (DatabaseIdProvider) resolveClass(type).getDeclaredConstructor().newInstance();
databaseIdProvider.setProperties(properties);
}
// 主配置赋值
Environment environment = configuration.getEnvironment();
if (environment != null && databaseIdProvider != null) {
String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
configuration.setDatabaseId(databaseId);
}
}
第十步： 解析 typeHandlers 节点 typeHandlerElement(root.evalNode("typeHandlers"));
xml示例
<typeHandlers>
<typeHandler handler="org.mybatis.example.ExampleTypeHandler"/>
</typeHandlers>
<typeHandlers>
<typeHandler handler="org.apache.ibatis.type.EnumOrdinalTypeHandler"
javaType="java.math.RoundingMode"/>
</typeHandlers>
<typeHandlers>
<package name="org.mybatis.example"/>
</typeHandlers>
private void typeHandlerElement(XNode parent) {
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);
if (javaTypeClass != null) {
if (jdbcType == null) {
typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
} else {
typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
}
} else {
typeHandlerRegistry.register(typeHandlerClass);
}
}
}
}
}
第十一步：xml sql语句加载 mapperElement(root.evalNode("mappers"));
xml 示例
<mappers>
<mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
</mappers>
<mappers>
<mapper url="file:///var/mappers/AuthorMapper.xml"/>
</mappers>
<mappers>
<mapper class="org.mybatis.builder.PostMapper"/>
</mappers>
<mappers>
<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())) {
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
// resource 类型的配置
// URL 和 resource 这个一样，只看一个
if (resource != null && url == null && mapperClass == null) {
ErrorContext.instance().resource(resource);
InputStream inputStream = Resources.getResourceAsStream(resource);
// 主要代码是这两句话。 下面看代码 👇👇
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
mapperParser.parse();
// url 类型的配置
} else if (resource == null && url != null && mapperClass == null) {
ErrorContext.instance().resource(url);
InputStream inputStream = Resources.getUrlAsStream(url);
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
mapperParser.parse();
// mapperClass 类型的配置
} else if (resource == null && url == null && mapperClass != null) {
// 反射加载mapper对象
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.");
}
}
}
}
}
// 构建XMLMapperBuilder对象
public XMLMapperBuilder(InputStream inputStream, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {
this(new XPathParser(inputStream, true, configuration.getVariables(), new XMLMapperEntityResolver()),
configuration, resource, sqlFragments);
}
public void parse() {
// 判断是否加载过，没加载的话执行后面逻辑
if (!configuration.isResourceLoaded(resource)) {
// 处理mapper sql语句的xml 👇下面看代码
configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();
}
<mapper namespace="com.mybatis.study.LogMapper">
<resultMap id="BaseResultMap" type="com.mybatis.study.Log">
<id column="id" jdbcType="INTEGER" property="id" />
<result column="username" jdbcType="VARCHAR" property="username" />
</resultMap>
<select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap">
select * from log where id = #{id,jdbcType=INTEGER}
</select>
</mapper>
private void configurationElement(XNode context) {
try {
// 熟悉的namespace，，不能为空
String namespace = context.getStringAttribute("namespace");
if (namespace == null || namespace.isEmpty()) {
throw new BuilderException("Mapper's namespace cannot be empty");
}
builderAssistant.setCurrentNamespace(namespace);
// 缓存相关的配置
cacheRefElement(context.evalNode("cache-ref"));
cacheElement(context.evalNode("cache"));
// 1️⃣ 参数映射（已废弃，不推荐使用） 这四块代码又很多。 看吧继续。👇下面代码
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
// 2️⃣ 结果映射
resultMapElements(context.evalNodes("/mapper/resultMap"));
// 3️⃣ sql语句
sqlElement(context.evalNodes("/mapper/sql"));
// 4️⃣ 根据语句类型构建
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);
}
}
这次先到这里吧，sql语句的解析在写篇文章放，这已经太多了。。
官方说明了已废弃，不再说了。 弃用!老式的参数映射方法。内联参数是首选的，这个元素将来可能会被删除。此处没有文档记录。
1️⃣参数处理
private void parameterMapElement(List<XNode> list) {
for (XNode parameterMapNode : list) {
String id = parameterMapNode.getStringAttribute("id");
String type = parameterMapNode.getStringAttribute("type");
Class<?> parameterClass = resolveClass(type);
List<XNode> parameterNodes = parameterMapNode.evalNodes("parameter");
List<ParameterMapping> parameterMappings = new ArrayList<>();
for (XNode parameterNode : parameterNodes) {
String property = parameterNode.getStringAttribute("property");
String javaType = parameterNode.getStringAttribute("javaType");
String jdbcType = parameterNode.getStringAttribute("jdbcType");
String resultMap = parameterNode.getStringAttribute("resultMap");
String mode = parameterNode.getStringAttribute("mode");
String typeHandler = parameterNode.getStringAttribute("typeHandler");
Integer numericScale = parameterNode.getIntAttribute("numericScale");
ParameterMode modeEnum = resolveParameterMode(mode);
Class<?> javaTypeClass = resolveClass(javaType);
JdbcType jdbcTypeEnum = resolveJdbcType(jdbcType);
Class<? extends TypeHandler<?>> typeHandlerClass = resolveClass(typeHandler);
ParameterMapping parameterMapping = builderAssistant.buildParameterMapping(parameterClass, property, javaTypeClass, jdbcTypeEnum, resultMap, modeEnum, typeHandlerClass, numericScale);
parameterMappings.add(parameterMapping);
}
builderAssistant.addParameterMap(id, parameterClass, parameterMappings);
}
}
2️⃣结果映射
private void resultMapElements(List<XNode> list) {
for (XNode resultMapNode : list) {
try {
resultMapElement(resultMapNode);
} catch (IncompleteElementException e) {
// ignore, it will be retried
}
}
}
3️⃣sql语句
private void sqlElement(List<XNode> list) {
if (configuration.getDatabaseId() != null) {
sqlElement(list, configuration.getDatabaseId());
}
sqlElement(list, null);
}
4️⃣ 根据语句类型构建
private void buildStatementFromContext(List<XNode> list) {
if (configuration.getDatabaseId() != null) {
buildStatementFromContext(list, configuration.getDatabaseId());
}
buildStatementFromContext(list, null);
}
