大家应该都知道Mybatis源码也是对Jbdc的再一次封装,不管怎么进行包装,还是会有获取链接、preparedStatement、封装参数、执行这些步骤的。
配置解析过程
String resource = "mybatis-config.xml"; //1.读取resources下面的mybatis-config.xml文件 InputStream inputStream = Resources.getResourceAsStream(resource); //2.使用SqlSessionFactoryBuilder创建SqlSessionFactory SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.通过sqlSessionFactory创建SqlSession SqlSession sqlSession = sqlSessionFactory.openSession();
1.Resources.getResourceAsStream(resource)读取文件
public static InputStream getResourceAsStream(String resource) throws IOException { return getResourceAsStream(null, resource); } //loader赋值为null public static InputStream getResourceAsStream(ClassLoader loader, String resource) throws IOException { InputStream in = classLoaderWrapper.getResourceAsStream(resource, loader); if (in == null) { throw new IOException("Could not find resource " + resource); } return in; } //classLoader为null public InputStream getResourceAsStream(String resource, ClassLoader classLoader) { return getResourceAsStream(resource, getClassLoaders(classLoader)); } //classLoader类加载 InputStream getResourceAsStream(String resource, ClassLoader[] classLoader) { for (ClassLoader cl : classLoader) { if (null != cl) { //加载指定路径文件流 InputStream returnValue = cl.getResourceAsStream(resource); // now, some class loaders want this leading "/", so we'll add it and try again if we didn't find the resource if (null == returnValue) { returnValue = cl.getResourceAsStream("/" + resource); } if (null != returnValue) { return returnValue; } } } return null;
总结:主要是通过ClassLoader.getResourceAsStream()方法获取指定的classpath路径下的Resource
2.通过SqlSessionFactoryBuilder创建SqlSessionFactory
//SqlSessionFactoryBuilder是一个建造者模式 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); public SqlSessionFactory build(InputStream inputStream) { return build(inputStream, null, null); } //XMLConfigBuilder也是建造者模式 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. } } } //接下来进入XMLConfigBuilder构造函数 public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) { this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props); } //接下来进入this后,初始化Configuration 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; } //其中parser.parse()负责解析xml,build(configuration)创建SqlSessionFactory return build(parser.parse())
（1）parser.parse()解析xml
public Configuration parse() { //判断是否重复解析 if (parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } parsed = true; //读取配置文件一级节点configuration parseConfiguration(parser.evalNode("/configuration")); return configuration; }
private void parseConfiguration(XNode root) { try { //properties 标签,用来配置参数信息，比如最常见的数据库连接信息 propertiesElement(root.evalNode("properties")); Properties settings = settingsAsProperties(root.evalNode("settings")); loadCustomVfs(settings); loadCustomLogImpl(settings); //实体别名两种方式:1.指定单个实体;2.指定包 typeAliasesElement(root.evalNode("typeAliases")); //插件 pluginElement(root.evalNode("plugins")); //用来创建对象(数据库数据映射成java对象时) objectFactoryElement(root.evalNode("objectFactory")); objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); reflectorFactoryElement(root.evalNode("reflectorFactory")); settingsElement(settings); // read it after objectFactory and objectWrapperFactory issue #631 //数据库环境 environmentsElement(root.evalNode("environments")); databaseIdProviderElement(root.evalNode("databaseIdProvider")); //数据库类型和Java数据类型的转换 typeHandlerElement(root.evalNode("typeHandlers")); //这个是对数据库增删改查的解析 mapperElement(root.evalNode("mappers")); } catch (Exception e) { throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); } }
总结:parseConfiguration完成的是解析configuration下的标签
private void mapperElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { //解析<package name=""/> if ("package".equals(child.getName())) { String mapperPackage = child.getStringAttribute("name"); //包路径存到mapperRegistry中 configuration.addMappers(mapperPackage); } else { //解析<mapper url="" class="" resource=""></mapper> 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); //读取Mapper.xml文件 InputStream inputStream = Resources.getResourceAsStream(resource); 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); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments()); mapperParser.parse(); } else if (resource == null && url == null && mapperClass != null) { 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."); } } } }
总结: 通过解析configuration.xml文件,获取其中的Environment、Setting,重要的是将下的所有解析出来之后添加到Configuration,Configuration类似于配置中心,所有的配置信息都在这里。
（2）mapperParser.parse()对 Mapper 映射器的解析
public void parse() { if (!configuration.isResourceLoaded(resource)) { //解析所有的子标签 configurationElement(parser.evalNode("/mapper")); configuration.addLoadedResource(resource); //把namespace（接口类型）和工厂类绑定起来 bindMapperForNamespace(); } parsePendingResultMaps(); parsePendingCacheRefs(); parsePendingStatements(); } //这里面解析的是Mapper.xml的标签 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); //对其他命名空间缓存配置的引用 cacheRefElement(context.evalNode("cache-ref")); //对给定命名空间的缓存配置 cacheElement(context.evalNode("cache")); parameterMapElement(context.evalNodes("/mapper/parameterMap")); //是最复杂也是最强大的元素，用来描述如何从数据库结果集中来加载对象 resultMapElements(context.evalNodes("/mapper/resultMap")); //可被其他语句引用的可重用语句块 sqlElement(context.evalNodes("/mapper/sql")); //获得MappedStatement对象(增删改查标签) 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); } } //获得MappedStatement对象(增删改查标签) private void buildStatementFromContext(List<XNode> list) { if (configuration.getDatabaseId() != null) { buildStatementFromContext(list, configuration.getDatabaseId()); } buildStatementFromContext(list, null); } //获得MappedStatement对象(增删改查标签) private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) { //循环增删改查标签 for (XNode context : list) { final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId); try { //解析insert/update/select/delete中的标签 statementParser.parseStatementNode(); } catch (IncompleteElementException e) { configuration.addIncompleteStatement(statementParser); } } } public void parseStatementNode() { //在命名空间中唯一的标识符,可以被用来引用这条语句 String id = context.getStringAttribute("id"); //数据库厂商标识 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; //flushCache和useCache都和二级缓存有关 //将其设置为true后,只要语句被调用,都会导致本地缓存和二级缓存被清空,默认值:false boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect); //将其设置为 true 后，将会导致本条语句的结果被二级缓存缓存起来，默认值：对 select 元素为 true 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()); //会传入这条语句的参数类的完全限定名或别名 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"); //从这条语句中返回的期望类型的类的完全限定名或别名 String resultType = context.getStringAttribute("resultType"); Class<?> resultTypeClass = resolveClass(resultType); //外部resultMap的命名引用 String resultMap = context.getStringAttribute("resultMap"); String resultSetType = context.getStringAttribute("resultSetType"); ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType); String keyProperty = context.getStringAttribute("keyProperty"); String keyColumn = context.getStringAttribute("keyColumn"); String resultSets = context.getStringAttribute("resultSets"); 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(); //持有在configuration中 configuration.addMappedStatement(statement); return statement; } public void addMappedStatement(MappedStatement ms){ //ms.getId = mapper.UserMapper.getUserById //ms = MappedStatement等于每一个增删改查的标签的里的数据 mappedStatements.put(ms.getId(), ms); } //最终存放到mappedStatements中,mappedStatements存放的是一个个的增删改查 protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>("Mapped Statements collection") .conflictMessageProducer((savedValue, targetValue) -> ". please check " + savedValue.getResource() + " and " + targetValue.getResource());
（3）解析bindMapperForNamespace()方法
把 namespace（接口类型）和工厂类绑定起来
private void bindMapperForNamespace() { //当前Mapper的命名空间 String namespace = builderAssistant.getCurrentNamespace(); if (namespace != null) { Class<?> boundType = null; try { //interface mapper.UserMapper这种 boundType = Resources.classForName(namespace); } catch (ClassNotFoundException e) {} if (boundType != null) { if (!configuration.hasMapper(boundType)) { configuration.addLoadedResource("namespace:" + namespace); 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 { //接口类型(key)->工厂类 knownMappers.put(type, new MapperProxyFactory<>(type)); MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type); parser.parse(); loadCompleted = true; } finally { if (!loadCompleted) { knownMappers.remove(type); } }
（4）(configuration)生成SqlSessionFactory对象
总结
XMLMapperBuilder.parse()方法,是对 Mapper 映射器的解析里面有两个方法：
- configurationElement()解析所有的子标签,最终解析Mapper.xml中的insert/update/delete/select标签的id(全路径)组成key和整个标签和数据连接组成MappedStatement存放到Configuration中的 mappedStatements这个map
- 里面。
- bindMapperForNamespace()是把接口类型(interface mapper.UserMapper)和工厂类存到放MapperRegistry中的knownMappers里面
3.SqlSessionFactory的创建
public SqlSessionFactory build(Configuration config) { return new DefaultSqlSessionFactory(config);
直接把Configuration当做参数,直接new一个DefaultSqlSessionFactory。
