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mybatis-启动源码分析

發布時間：2023/12/3 编程问答 36 豆豆

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【1】測試用例

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="dbconfig.properties"></properties><settings><setting name="mapUnderscoreToCamelCase" value="false"/><setting name="lazyLoadingEnabled" value="true"/><setting name="aggressiveLazyLoading" value="false"/></settings><typeAliases><package name="com.swjtu.mybatis.bean"/></typeAliases> <environments default="development"><environment id="test"><transactionManager type="JDBC"/><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><environment id="development"><transactionManager type="JDBC"/><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> <databaseIdProvider type="DB_VENDOR"><property name="Mysql" value="mysql"/><property name="Oracle" value="oracle"/><property name="SQL Server" value="sqlserver"/></databaseIdProvider>  <mappers><mapper resource="com\swjtu\mybatis\dao\EmployeeMapper.xml"/> </mappers></configuration>

執行sql；

public static void main1() {/*1. 獲取 SqlSessionFactory 對象*/SqlSessionFactory sqlSessionFactory = MyBatisUtils.getSqlSessionFactory();/*2.獲取SqlSession對象, 不會自動提交數據*/SqlSession session = sqlSessionFactory.openSession();try { String flag = "0911A"; List<Map<String, Object>> list = new ArrayList<>();for (int i = 0; i < 5; i++) { String indexFormat = String.format("%8d", i);Map<String, Object> map = new HashMap<>(); map.put("RCRD_ID", flag + indexFormat); map.put("CUST_NUM", "CUST_NUM" +flag+ indexFormat);map.put("CUST_NAME", "CUST_NAME" +flag+ indexFormat);map.put("WARN_TIMES", i); list.add(map); } // mapper.insert2CustWarn(list);session.insert("com.swjtu.mybatis.dao.EmployeeMapper.insert2CustWarn", list); session.commit();} finally { session.close();}System.out.println("bingo!");} mapper文件中的 dml 元素 <insert id="insert2CustWarn">INSERT INTO my_cust_warn_tbl(rcrd_id, cust_num, cust_name , warn_times) VALUES <foreach collection="list" item="item" separator=",">(#{item.RCRD_ID}, #{item.CUST_NUM}, #{item.CUST_NAME}, #{item.WARN_TIMES})</foreach></insert>

MyBatisUtils.getSqlSessionFactory();

/*** 獲取SqlSessionFactory * @return*/ public final static SqlSessionFactory getSqlSessionFactory() {String resource = "mybatis-config.xml";InputStream inputStream;try { inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);return sqlSessionFactory;} catch (IOException e) {e.printStackTrace();}return null; }

【2】創建 SqlSessionFactory 對象

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

實際上返回的是? DefaultSqlSessionFactory；

// SqlSessionFactoryBuilder 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);}

?而 build(Configuration config) 中的 config 是從mybatis-config.xml文件解析而來的；

【2.1】XMLConfigBuilder.parse() 產生Configuration

parser.parse() 方法的邏輯如下（XMLConfigBuilder構造器中新建了 Configuration對象）：

// SqlSessionFactoryBuilder private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {super(new Configuration());// 新建了一個 configuration對象ErrorContext.instance().resource("SQL Mapper Configuration");this.configuration.setVariables(props);this.parsed = false;this.environment = environment;this.parser = parser;}public Configuration parse() {if (parsed) {throw new BuilderException("Each XMLConfigBuilder can only be used once.");}parsed = true;parseConfiguration(parser.evalNode("/configuration"));// 解析xml節點return configuration;}private void parseConfiguration(XNode root) {// 解析xml節點try {Properties settings = settingsAsPropertiess(root.evalNode("settings"));//issue #117 read properties firstpropertiesElement(root.evalNode("properties"));loadCustomVfs(settings);typeAliasesElement(root.evalNode("typeAliases"));pluginElement(root.evalNode("plugins"));objectFactoryElement(root.evalNode("objectFactory"));objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));reflectorFactoryElement(root.evalNode("reflectorFactory"));settingsElement(settings);// read it after objectFactory and objectWrapperFactory issue #631environmentsElement(root.evalNode("environments"));databaseIdProviderElement(root.evalNode("databaseIdProvider"));typeHandlerElement(root.evalNode("typeHandlers"));mapperElement(root.evalNode("mappers"));} catch (Exception e) {throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);}}

我們跟蹤了 mapperElement(..)? 方法，它是解析 mybatis-config.xml 文件中在 mapper標簽中配置的resource屬性指定的sql mapper文件，比如：

?其中 root.evalNode("mappers") 獲取的值就是 mapper 數組；?

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");if (resource != null && url == null && mapperClass == null) {ErrorContext.instance().resource(resource);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.");}}}}}

Xnode parent 長這樣（就是 mybatis-config.xml 中 mappers元素內容）：

以上代碼，我們發現，解析 mapper有三種方式；

1.通過resource 配置；
2.通過url；
3.通過mapper class；

下面，我們以resource 為例來講解；

if (resource != null && url == null && mapperClass == null) {ErrorContext.instance().resource(resource);InputStream inputStream = Resources.getResourceAsStream(resource);XMLMapperBuilder mapperParser = new XMLMapperBuilder (inputStream, configuration, resource, configuration.getSqlFragments());mapperParser.parse(); }

以上代碼發現，每一個mapper文件，都會創建一個 XMLMapperBuilder 對象來解析它；

String resource=“com\swjtu\mybatis\dao\EmployeeMapper.xml”;

XMLMapperBuilder構造器傳入了4個參數

?mapper文件的輸入流（com\swjtu\mybatis\dao\EmployeeMapper.xml文件流）；

mybatis配置對象Configuration；

resource（sql文件名稱com\swjtu\mybatis\dao\EmployeeMapper.xml）；

sqlFragments-sql片段為空；

XMLMapperBuilder構造器；該構造器新建了 MapperBuilderAssistant對象（解析mapper文件的助手）；

public XMLMapperBuilder(InputStream inputStream, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {this(new XPathParser(inputStream, true, configuration.getVariables(), new XMLMapperEntityResolver()),configuration, resource, sqlFragments);}private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {super(configuration);this.builderAssistant = new MapperBuilderAssistant(configuration, resource);this.parser = parser;this.sqlFragments = sqlFragments;this.resource = resource;}

MapperBuilderAssistant() 長這個樣子；

?【2.2】XmlMapperBuilder().parse()? 解析mappers下的每個mapper文件內容

接著，進入? XmlMapperBuilder().parse() 方法，解析mappers下的mapper元素的內容，mapper元素如 ??? <mapper resource="com\swjtu\mybatis\dao\EmployeeMapper.xml"/>??? ；如下：

代碼步驟：

step1）解析mapper文件下 mapper元素內容（主要是 dml標簽元素內容）；
step2）把mapper文件名添加到 configuration，以避免二次解析；
step3）構建命名空間；

【2.2.1】 XmlMapperBuilder.configurationElement(parser.evalNode("/mapper"))如下：?

其中 parser.evalNode("/mapper")或context就是文件 com\swjtu\mybatis\dao\EmployeeMapper.xml? 的內容，如下：

代碼步驟：

step1）設置命名空間；
step2）解析緩存；
step3）解析 parameterMap 標簽內容；
step4）解析 resultMap 標簽內容；
step5）解析 sql 標簽內容；
step6）解析 sql 的dml 標簽內容（select或insert或update 或 delete）；

最后一步， buildStatementFromContext(context.evalNodes("select|insert|update|delete")); 就是真正解析 sql的 dml語句的標簽了，即解析出sql文本并加載到內存中；?

List<XNode>? list 包含了多個 dml標簽的內容數組；

接著 buildStatementFromContext(List<XNode> list, String requiredDatabaseId) 遍歷list中的每個dml 標簽元素；? 如下：

private void buildStatementFromContext(List<XNode> list) {if (configuration.getDatabaseId() != null) {buildStatementFromContext(list, configuration.getDatabaseId());}buildStatementFromContext(list, null);}private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {for (XNode context : list) {final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);try {statementParser.parseStatementNode();} catch (IncompleteElementException e) {configuration.addIncompleteStatement(statementParser);}}}

以上代碼，每個 dml標簽元素就會創建一個 XMLStatementBuilder 對象；

statementParser.parseStatementNode();?

就用于解析 context 文本（dml標簽元素內容）；如下：

public void parseStatementNode() {String id = context.getStringAttribute("id");String databaseId = context.getStringAttribute("databaseId");if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {return;}Integer fetchSize = context.getIntAttribute("fetchSize");Integer timeout = context.getIntAttribute("timeout");String parameterMap = context.getStringAttribute("parameterMap");String parameterType = context.getStringAttribute("parameterType");Class<?> parameterTypeClass = resolveClass(parameterType);String resultMap = context.getStringAttribute("resultMap");String resultType = context.getStringAttribute("resultType");String lang = context.getStringAttribute("lang");LanguageDriver langDriver = getLanguageDriver(lang);Class<?> resultTypeClass = resolveClass(resultType);String resultSetType = context.getStringAttribute("resultSetType");StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);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 parsingXMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);includeParser.applyIncludes(context.getNode());// Parse selectKey after includes and remove them.processSelectKeyNodes(id, parameterTypeClass, langDriver);// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);String resultSets = context.getStringAttribute("resultSets");String keyProperty = context.getStringAttribute("keyProperty");String keyColumn = context.getStringAttribute("keyColumn");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))? new Jdbc3KeyGenerator() : new NoKeyGenerator();}builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,resultSetTypeEnum, flushCache, useCache, resultOrdered, keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);}

以上代碼的步驟如下：

step1）解析 dml元素中各種屬性，包括 parameterMap，parameterType，resultMap，resultType等；

Integer fetchSize = context.getIntAttribute("fetchSize");Integer timeout = context.getIntAttribute("timeout");String parameterMap = context.getStringAttribute("parameterMap");String parameterType = context.getStringAttribute("parameterType");Class<?> parameterTypeClass = resolveClass(parameterType);String resultMap = context.getStringAttribute("resultMap");String resultType = context.getStringAttribute("resultType");

resultType 為map；因為 dml標簽元素如下：

<select id="getEmpByLastNameLikeReturnMap" resultType="map">SELECT id AS ID, last_name AS LASTNAME, email AS EMAIL, gender AS GENDERFROM emp_tbl WHERE last_name like #{lastName}</select>

step2）獲取語言驅動器， LanguageDriver langDriver = getLanguageDriver(lang);

step3）??? Class<?> resultTypeClass = resolveClass(resultType);：返回 resultType的class類型；如 resultType為map，則返回 Map.class ;

protected Class<?> resolveClass(String alias) { // 以alias為map為例if (alias == null) {return null;}try {return resolveAlias(alias);} catch (Exception e) {throw new BuilderException("Error resolving class. Cause: " + e, e);}} // BaseBuilder.java protected Class<?> resolveAlias(String alias) {return typeAliasRegistry.resolveAlias(alias);}public <T> Class<T> resolveAlias(String string) {try {if (string == null) {return null;}// issue #748String key = string.toLowerCase(Locale.ENGLISH);Class<T> value;if (TYPE_ALIASES.containsKey(key)) {value = (Class<T>) TYPE_ALIASES.get(key);} else {value = (Class<T>) Resources.classForName(string);}return value;} catch (ClassNotFoundException e) {throw new TypeException("Could not resolve type alias '" + string + "'. Cause: " + e, e);}}

typeAliasRegistry 為類型別名注冊器，如下：

public TypeAliasRegistry() {registerAlias("string", String.class);registerAlias("byte", Byte.class);registerAlias("long", Long.class);registerAlias("short", Short.class);registerAlias("int", Integer.class);registerAlias("integer", Integer.class);registerAlias("double", Double.class);registerAlias("float", Float.class);registerAlias("boolean", Boolean.class);registerAlias("byte[]", Byte[].class);registerAlias("long[]", Long[].class);registerAlias("short[]", Short[].class);registerAlias("int[]", Integer[].class);registerAlias("integer[]", Integer[].class);registerAlias("double[]", Double[].class);registerAlias("float[]", Float[].class);registerAlias("boolean[]", Boolean[].class);registerAlias("_byte", byte.class);registerAlias("_long", long.class);registerAlias("_short", short.class);registerAlias("_int", int.class);registerAlias("_integer", int.class);registerAlias("_double", double.class);registerAlias("_float", float.class);registerAlias("_boolean", boolean.class);registerAlias("_byte[]", byte[].class);registerAlias("_long[]", long[].class);registerAlias("_short[]", short[].class);registerAlias("_int[]", int[].class);registerAlias("_integer[]", int[].class);registerAlias("_double[]", double[].class);registerAlias("_float[]", float[].class);registerAlias("_boolean[]", boolean[].class);registerAlias("date", Date.class);registerAlias("decimal", BigDecimal.class);registerAlias("bigdecimal", BigDecimal.class);registerAlias("biginteger", BigInteger.class);registerAlias("object", Object.class);registerAlias("date[]", Date[].class);registerAlias("decimal[]", BigDecimal[].class);registerAlias("bigdecimal[]", BigDecimal[].class);registerAlias("biginteger[]", BigInteger[].class);registerAlias("object[]", Object[].class);registerAlias("map", Map.class);registerAlias("hashmap", HashMap.class);registerAlias("list", List.class);registerAlias("arraylist", ArrayList.class);registerAlias("collection", Collection.class);registerAlias("iterator", Iterator.class);registerAlias("ResultSet", ResultSet.class);}

step4）獲取sql語句類型， PREPARED ；

step5）獲取sql命令類型 SqlCommandType -SELECT

String nodeName = context.getNode().getNodeName(); // nodeName為selectSqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));public enum SqlCommandType {UNKNOWN, INSERT, UPDATE, DELETE, SELECT, FLUSH; }

step6）解析是否需要使用緩存

boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);//false boolean useCache = context.getBooleanAttribute("useCache", isSelect);//true boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);//false

step7）解析dml元素中 include元素內容（比如 include sql）；

XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);includeParser.applyIncludes(context.getNode());

public void applyIncludes(Node source) {Properties variablesContext = new Properties();Properties configurationVariables = configuration.getVariables();if (configurationVariables != null) {variablesContext.putAll(configurationVariables);}applyIncludes(source, variablesContext);}

?step8）解析 selectKey；sql中沒有，不用考慮；

processSelectKeyNodes(id, parameterTypeClass, langDriver);

?step9）創建sql 映射對象；

SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);

langDriver 指向了 org.apache.ibatis.scripting.xmltags.XMLLanguageDriver；

public class XMLLanguageDriver implements LanguageDriver {@Overridepublic ParameterHandler createParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {return new DefaultParameterHandler(mappedStatement, parameterObject, boundSql);}@Overridepublic SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) {XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType);return builder.parseScriptNode();}@Overridepublic SqlSource createSqlSource(Configuration configuration, String script, Class<?> parameterType) {// issue #3if (script.startsWith("<script>")) {XPathParser parser = new XPathParser(script, false, configuration.getVariables(), new XMLMapperEntityResolver());return createSqlSource(configuration, parser.evalNode("/script"), parameterType);} else {// issue #127script = PropertyParser.parse(script, configuration.getVariables());TextSqlNode textSqlNode = new TextSqlNode(script);if (textSqlNode.isDynamic()) {return new DynamicSqlSource(configuration, textSqlNode);} else {return new RawSqlSource(configuration, script, parameterType);}}}}

builder.parseScriptNode()? 調用的是 XMLScriptBuilder.parseScriptNode() ；解析動態sql （用${} 包裹的sql ）；

public SqlSource parseScriptNode() {List<SqlNode> contents = parseDynamicTags(context);MixedSqlNode rootSqlNode = new MixedSqlNode(contents);SqlSource sqlSource = null;if (isDynamic) {sqlSource = new DynamicSqlSource(configuration, rootSqlNode);} else {sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);}return sqlSource;}List<SqlNode> parseDynamicTags(XNode node) {List<SqlNode> contents = new ArrayList<SqlNode>();NodeList children = node.getNode().getChildNodes();for (int i = 0; i < children.getLength(); i++) {XNode child = node.newXNode(children.item(i));if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE || child.getNode().getNodeType() == Node.TEXT_NODE) {String data = child.getStringBody("");TextSqlNode textSqlNode = new TextSqlNode(data);if (textSqlNode.isDynamic()) {contents.add(textSqlNode);isDynamic = true;} else {contents.add(new StaticTextSqlNode(data));}} else if (child.getNode().getNodeType() == Node.ELEMENT_NODE) { // issue #628String nodeName = child.getNode().getNodeName();NodeHandler handler = nodeHandlers(nodeName);if (handler == null) {throw new BuilderException("Unknown element <" + nodeName + "> in SQL statement.");}handler.handleNode(child, contents);isDynamic = true;}}return contents;}

因為我們不是動態sql，所以返回的是 RawSqlSource；

sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);

step10）解析 resultSets， keyProperty， keyColumn 屬性等（也不用太關心）；?

String resultSets = context.getStringAttribute("resultSets");String keyProperty = context.getStringAttribute("keyProperty");String keyColumn = context.getStringAttribute("keyColumn");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))? new Jdbc3KeyGenerator() : new NoKeyGenerator();}

step11）MapperBuilderAssistant.addMappedStatement() 把解析得到的sql映射對象添加到configuration；

builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,resultSetTypeEnum, flushCache, useCache, resultOrdered, keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);

參數列表如下：

1.id，getEmpByLastNameLikeReturnMap；
2.sqlSource，

?parameterMappins 明顯是參數映射；

3.statementType ， PREPARED；
4.sqlCommandType，SELECT;
5.fetchSize，null；
6.timeout， null；
7.parameterMap，null；
8.parameterTypeClass，null；
9.resultMap，null；
10.resultTypeClass， interface java.util.Map；
11.resultSetTypeEnum，null；
12.flushCache，false；
13.useCache，true；
14.resultOrdered，false；
15.keyGenerator，org.apache.ibatis.executor.keygen.NoKeyGenerator@5ef8df1e；
16.keyProperty，null；
17.keyColumn，null；
18.databaseId，null；
19.langDriver， org.apache.ibatis.scripting.xmltags.XMLLanguageDriver@32057e6；
20.resultSets, null；

MapperBuilderAssistant.addMappedStatement(...)? 源碼如下：

public MappedStatement addMappedStatement(...) {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();configuration.addMappedStatement(statement);return statement;}

id = applyCurrentNamespace(id, false); 這一步，給id添加命名空間前綴，

執行前；id為? getEmpByLastNameLikeReturnMap ；
執行后，id為 com.swjtu.mybatis.dao.EmployeeMapper.getEmpByLastNameLikeReturnMap；

解析每個dml元素時，都要創建一個? MappedStatement.Builder(...) 用于創建 MappedStatement（ sql映射信息）

MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType)

MappedStatement statement = statementBuilder.build(); 源碼如下：

public MappedStatement build() {assert mappedStatement.configuration != null;assert mappedStatement.id != null;assert mappedStatement.sqlSource != null;assert mappedStatement.lang != null;mappedStatement.resultMaps = Collections.unmodifiableList(mappedStatement.resultMaps);return mappedStatement;}

補充：MappedStatement對象

MappedStatement 實際是封裝了 sql映射信息的對象，sql映射是在 MapperBuilderAssistant.addMappedStatement(...) 方法里面構建；結構如下：

每條sql都是一個 MappedStatement對象，解析完成后，將其添加到 configuration對象中；

?configuration 就是根據mybatis-config.xml 文件解析出的 Configuration 對象；長這個樣子：

【2.2.2】 configuration.addLoadedResource(resource);

把已經解析的resource 文件名添加到 configuration，避免二次解析；

【2.2.3】XMLMapperBuilder.bindMapperForNamespace() 創建命名空間

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#loadXmlResourceconfiguration.addLoadedResource("namespace:" + namespace);configuration.addMapper(boundType);}}}}public <T> void addMapper(Class<T> type) {mapperRegistry.addMapper(type);}

很顯然，當有mapperclass的時候，才會設置 boundType；如果沒有mapper class也沒有關系；因為catch會忽略異常；

【2.2.4】解析其他

parsePendingResultMaps();parsePendingChacheRefs();parsePendingStatements();

【2.2.5】創建 DefaultSqlSession對象并返回

解析完成后，生成Configuration對象;

【3】sqlSessionFactory.openSession()打開會話

調用的是 DefaultSqlSessionFactory.openSession()

// DefaultSqlSessionFactory @Overridepublic SqlSession openSession() {return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);}private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx = null;try {final Environment environment = configuration.getEnvironment();final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);final Executor executor = configuration.newExecutor(tx, execType);// 返回的是 DefaultSqlSession return new DefaultSqlSession(configuration, executor, autoCommit);} catch (Exception e) {closeTransaction(tx); // may have fetched a connection so lets call close()throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);} finally {ErrorContext.instance().reset();}}

【3.1】DefaultSqlSessionFactory 中有兩類方法包括，

從數據源獲取會話：private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit)；

從連接中獲取會話：private SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) ；

兩者不同點在于

tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);

final Transaction tx = transactionFactory.newTransaction(connection);

// 從數據源獲取會話 private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx = null;try {final Environment environment = configuration.getEnvironment();final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);// 創建事務工廠tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);// 創建事務 final Executor executor = configuration.newExecutor(tx, execType);// 執行器 return new DefaultSqlSession(configuration, executor, autoCommit);// 會話} catch (Exception e) {closeTransaction(tx); // may have fetched a connection so lets call close()throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);} finally {ErrorContext.instance().reset();}}// 從數據庫連接獲取會話 private SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {try {boolean autoCommit;try {autoCommit = connection.getAutoCommit();} catch (SQLException e) {// Failover to true, as most poor drivers// or databases won't support transactionsautoCommit = true;} final Environment environment = configuration.getEnvironment();final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);final Transaction tx = transactionFactory.newTransaction(connection);final Executor executor = configuration.newExecutor(tx, execType);return new DefaultSqlSession(configuration, executor, autoCommit);} catch (Exception e) {throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);} finally {ErrorContext.instance().reset();}}

獲取會話無論采用 datasource，還是connection方式，其步驟如下：

step1）獲取環境對象；
step2）獲取事務工廠；
step3）創建事務；
step4）創建執行器；
step5）創建會話 DefaultSqlSession；

【3.2】事務工廠

// 從環境對象中獲取事務工廠private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {if (environment == null || environment.getTransactionFactory() == null) {return new ManagedTransactionFactory();}return environment.getTransactionFactory();}

如果配置了環境元素，則返回配置的環境的事務工廠；否則默認返回 ManagedTransactionFactory；

此外，事務工廠有3個，如下：

【3.3】創建事務-ManagedTransaction

// 可管理的事務工廠 public class ManagedTransactionFactory implements TransactionFactory {private boolean closeConnection = true;@Overridepublic void setProperties(Properties props) {if (props != null) {String closeConnectionProperty = props.getProperty("closeConnection");if (closeConnectionProperty != null) {closeConnection = Boolean.valueOf(closeConnectionProperty);}}}@Overridepublic Transaction newTransaction(Connection conn) {return new ManagedTransaction(conn, closeConnection);} // 創建事務對象@Overridepublic Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit) {// Silently ignores autocommit and isolation level, as managed transactions are entirely// controlled by an external manager. It's silently ignored so that// code remains portable between managed and unmanaged configurations.return new ManagedTransaction(ds, level, closeConnection);} }

可管理事務： ManagedTransaction；?

public class ManagedTransaction implements Transaction {private static final Log log = LogFactory.getLog(ManagedTransaction.class);private DataSource dataSource;private TransactionIsolationLevel level;private Connection connection;private boolean closeConnection;public ManagedTransaction(Connection connection, boolean closeConnection) {this.connection = connection;this.closeConnection = closeConnection;}public ManagedTransaction(DataSource ds, TransactionIsolationLevel level, boolean closeConnection) {this.dataSource = ds;this.level = level;this.closeConnection = closeConnection;}@Overridepublic Connection getConnection() throws SQLException {if (this.connection == null) {openConnection();}return this.connection;}@Overridepublic void commit() throws SQLException {// Does nothing}@Overridepublic void rollback() throws SQLException {// Does nothing}@Overridepublic void close() throws SQLException {if (this.closeConnection && this.connection != null) {if (log.isDebugEnabled()) {log.debug("Closing JDBC Connection [" + this.connection + "]");}this.connection.close();}}protected void openConnection() throws SQLException {if (log.isDebugEnabled()) {log.debug("Opening JDBC Connection");}this.connection = this.dataSource.getConnection();if (this.level != null) {this.connection.setTransactionIsolation(this.level.getLevel());}}}

?它的commit， rollback 都是空的；

它的數據庫連接的獲取有兩種方式，

上游給定，傳入 Connection ;

通過 datasource 數據源獲取connection；

【3.4】創建執行器

1）ExecutorType 是枚舉類型，默認為SIMPLE ；

final Executor executor = configuration.newExecutor(tx, execType);// Configuration.newExecutor 方法 public Executor newExecutor(Transaction transaction, ExecutorType executorType) {executorType = executorType == null ? defaultExecutorType : executorType;executorType = executorType == null ? ExecutorType.SIMPLE : executorType;Executor executor;if (ExecutorType.BATCH == executorType) {executor = new BatchExecutor(this, transaction);} else if (ExecutorType.REUSE == executorType) {executor = new ReuseExecutor(this, transaction);} else {executor = new SimpleExecutor(this, transaction);}if (cacheEnabled) {executor = new CachingExecutor(executor);}executor = (Executor) interceptorChain.pluginAll(executor);return executor;}

如果為SIMPLE,則返回 SimpleExecutor 執行器；? 但如果啟用緩存，則封裝SimpleExecutor到緩存執行器；

最后把執行器添加到攔截器列表，攔截器 Interceptor 列表如下，本質上是一個 ArrayList數組；

// 攔截器 public class InterceptorChain {private final List<Interceptor> interceptors = new ArrayList<Interceptor>();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);}}

其中SimpleExecutor父類Executor的實現類包括

2）SimpleExecutor 長這個樣子

public class SimpleExecutor extends BaseExecutor {public SimpleExecutor(Configuration configuration, Transaction transaction) {super(configuration, transaction);}@Overridepublic int doUpdate(MappedStatement ms, Object parameter) throws SQLException {Statement stmt = null;try {Configuration configuration = ms.getConfiguration();StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);stmt = prepareStatement(handler, ms.getStatementLog());return handler.update(stmt);} finally {closeStatement(stmt);}}@Overridepublic <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {Statement stmt = null;try {Configuration configuration = ms.getConfiguration();StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);stmt = prepareStatement(handler, ms.getStatementLog());return handler.<E>query(stmt, resultHandler);} finally {closeStatement(stmt);}}@Overrideprotected <E> Cursor<E> doQueryCursor(MappedStatement ms, Object parameter, RowBounds rowBounds, BoundSql boundSql) throws SQLException {Configuration configuration = ms.getConfiguration();StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, null, boundSql);Statement stmt = prepareStatement(handler, ms.getStatementLog());return handler.<E>queryCursor(stmt);}@Overridepublic List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException {return Collections.emptyList();}private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {Statement stmt;Connection connection = getConnection(statementLog);stmt = handler.prepare(connection, transaction.getTimeout());handler.parameterize(stmt);return stmt;}}

【3.5】創建會話 DefaultSqlSession

public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {this.configuration = configuration;this.executor = executor;this.dirty = false;this.autoCommit = autoCommit;}

【4】session.insert(...)

【4.1】DefaultSqlSession.insert()?

session.insert(...); 它實際調用的是 DefaultSqlSession.insert() 方法；

// DefaultSqlSession @Overridepublic int insert(String statement, Object parameter) {return update(statement, parameter);}@Overridepublic int update(String statement) {return update(statement, null);}@Overridepublic int update(String statement, Object parameter) {try {dirty = true;MappedStatement ms = configuration.getMappedStatement(statement);return executor.update(ms, wrapCollection(parameter));} catch (Exception e) {throw ExceptionFactory.wrapException("Error updating database. Cause: " + e, e);} finally {ErrorContext.instance().reset();}}

?executor.update(ms, warpCollection(parameter)); 中的? executor是 SimpleExecutor;

我們接著看下 SimpleExecutor-執行器；

// 簡單執行器 public class SimpleExecutor extends BaseExecutor {public SimpleExecutor(Configuration configuration, Transaction transaction) {super(configuration, transaction);}// 執行器基類 public abstract class BaseExecutor implements Executor {private static final Log log = LogFactory.getLog(BaseExecutor.class);protected Transaction transaction;protected Executor wrapper;protected ConcurrentLinkedQueue<DeferredLoad> deferredLoads;protected PerpetualCache localCache;protected PerpetualCache localOutputParameterCache;protected Configuration configuration;protected int queryStack = 0;private boolean closed;protected BaseExecutor(Configuration configuration, Transaction transaction) {this.transaction = transaction;this.deferredLoads = new ConcurrentLinkedQueue<DeferredLoad>();this.localCache = new PerpetualCache("LocalCache");this.localOutputParameterCache = new PerpetualCache("LocalOutputParameterCache");this.closed = false;this.configuration = configuration;this.wrapper = this;}

BaseExecutor.update(MappedStatement ms, Object parameter) 如下：

@Overridepublic int update(MappedStatement ms, Object parameter) throws SQLException {ErrorContext.instance().resource(ms.getResource()).activity("executing an update").object(ms.getId());if (closed) {throw new ExecutorException("Executor was closed.");}clearLocalCache();return doUpdate(ms, parameter);}

SimpleExecutor.doUpdate(...)

@Overridepublic int doUpdate(MappedStatement ms, Object parameter) throws SQLException {Statement stmt = null;try {Configuration configuration = ms.getConfiguration();StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);stmt = prepareStatement(handler, ms.getStatementLog());return handler.update(stmt);} finally {closeStatement(stmt);}}

上述是執行sql 語句的地方，依賴的對象包括：

configuration：根據mybatis-config.xml 解析得到的配置對象；

StatementHandler：語句處理器；

PreparedStatement：預編譯語句；

Configuration.newStatementHandler(...) 方法如下：

public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);return statementHandler;}

參數列表為：

參數1-executor；

參數2-mappedStatement；?

參數3-parameterObject；

參數4- parameterObject 為：

{collection=[{RCRD_ID=0908A 0,CUST_NUM=CUST_NUM 0,WARN_TIMES=0,CUST_NAME=CUST_NAME 0},{RCRD_ID=0908A 1,CUST_NUM=CUST_NUM 1,WARN_TIMES=1,CUST_NAME=CUST_NAME 1},{RCRD_ID=0908A 2,CUST_NUM=CUST_NUM 2,WARN_TIMES=2,CUST_NAME=CUST_NAME 2},...],list=[{RCRD_ID=0908A 0,CUST_NUM=CUST_NUM 0,WARN_TIMES=0,CUST_NAME=CUST_NAME 0},{RCRD_ID=0908A 1,CUST_NUM=CUST_NUM 1,WARN_TIMES=1,CUST_NAME=CUST_NAME 1},{RCRD_ID=0908A 2,CUST_NUM=CUST_NUM 2,WARN_TIMES=2,CUST_NAME=CUST_NAME 2},]}

參數5-rowBounds?

?參數6-resultHandler 為null；

參數7-boundSql 為null ；

SimpleExecutor.newStatementHandler(...) 如下：

delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);

代碼步驟：

step1）獲取mybatis 配置對象；

step2）獲取 StatementHandler；

StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);

StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);// 新建語句處理器public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);return statementHandler;}

step3）prepareStatement(StatementHandler handler, Log statementLog) ，把預編譯sql 的參數賦值；

handler 為 PreparedStatementHandler ；

step3.1）stmt = handler.prepare(connection, transaction.getTimeout()); 獲取預編譯語句；

// RoutingStatementHandler @Overridepublic Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {return delegate.prepare(connection, transactionTimeout);}// BaseStatemetnHandler@Overridepublic Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {ErrorContext.instance().sql(boundSql.getSql());Statement statement = null;try {statement = instantiateStatement(connection);setStatementTimeout(statement, transactionTimeout);setFetchSize(statement);return statement;} catch (SQLException e) {closeStatement(statement);throw e;} catch (Exception e) {closeStatement(statement);throw new ExecutorException("Error preparing statement. Cause: " + e, e);}}

step3.2）handler.parameterize(stmt); 對參數進行賦值；

// RoutingStatementHandler@Overridepublic void parameterize(Statement statement) throws SQLException {delegate.parameterize(statement);}// PreparedStatementHandler @Overridepublic void parameterize(Statement statement) throws SQLException {parameterHandler.setParameters((PreparedStatement) statement);}//

parameterHandler.setParameters(...) ；源碼如下：

遍歷 sql語句中所有參數，并賦值；

public void setParameters(PreparedStatement ps) {ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();if (parameterMappings != null) {for (int i = 0; i < parameterMappings.size(); i++) {ParameterMapping parameterMapping = parameterMappings.get(i);if (parameterMapping.getMode() != ParameterMode.OUT) {Object value;String propertyName = parameterMapping.getProperty();if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional paramsvalue = boundSql.getAdditionalParameter(propertyName);} else if (parameterObject == null) {value = null;} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {value = parameterObject;} else {MetaObject metaObject = configuration.newMetaObject(parameterObject);value = metaObject.getValue(propertyName);}TypeHandler typeHandler = parameterMapping.getTypeHandler();JdbcType jdbcType = parameterMapping.getJdbcType();if (value == null && jdbcType == null) {jdbcType = configuration.getJdbcTypeForNull();}try {typeHandler.setParameter(ps, i + 1, value, jdbcType);} catch (TypeException e) {throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);} catch (SQLException e) {throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);}}}

?parameterMappings 是參數信息，如CUST_NUM ；??

?boundsql 是預編譯sql，帶有問號；?

?設置參數；

step4）handler.update() 執行具體 sql； ?

@Overridepublic int update(Statement statement) throws SQLException {return delegate.update(statement);} // delegate 代理為 PreparedStatementHandler

執行具體sql，如下：

@Overridepublic int update(Statement statement) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;ps.execute(); // 執行sql int rows = ps.getUpdateCount(); // 獲取更新行數 Object parameterObject = boundSql.getParameterObject();KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);return rows;}

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