Mybatis系列十六：源码解析-SqlSessionFactory

比眉伴天荒 2022-02-13 05:06 337阅读 0赞

mybatis全局配置文件mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
     PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
     "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
    	<environments default="development">
    		<environment id="development">
    			<transactionManager type="JDBC" />
    			<dataSource type="POOLED">
    				<property name="driver" value="com.mysql.jdbc.Driver" />
    				<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
    				<property name="username" value="root" />
    				<property name="password" value="root" />
    			</dataSource>
    		</environment>
    	</environments>
    	
    	<mappers>
    		<mapper resource="EmployeeMapper.xml" />
    	</mappers>
    </configuration>

mapper映射文件EmployeeMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper
     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapper">
    
    
    	<select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee">
    		select id,last_name lastName,email,gender from tbl_employee where id = #{id}
    	</select>
    </mapper>

测试方法：

/**
    	 * 1、获取sqlSessionFactory对象
    	 * 		解析文件的每一个信息保存在Configuration中，然后返回包含Configuration的DefaultSqlSession。
    	 * 		MappedStatement：代表一个增删改查的详细信息
    	 * 2、获取sqlSession对象
    	 * 3、获取接口的代理对象
    	 * 4、执行增删改查方法
    	 * @throws IOException
    	 */
    	@Test
    	public void test() throws IOException {
    		//1、获取sqlSessionFactory对象
    		String resource = "mybatis-config.xml";
    		InputStream inputStream = Resources.getResourceAsStream(resource);
    		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    		//2、获取sqlSession对象
    		SqlSession openSession = sqlSessionFactory.openSession();
    		try {
    			//3、获取接口的代理对象
    			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    			//4、执行增删改查方法
    			Employee employee = mapper.getEmpById(1);
    			System.out.println(mapper);
    			System.out.println(employee);
    		} finally {
    			openSession.close();
    		}
    	}

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源码解析：  
一、获取sqlSessionFactory对象

String resource = "mybatis-config.xml";
    	InputStream inputStream = Resources.getResourceAsStream(resource);
    	SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

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1、SqlSessionFactoryBuilder

public SqlSessionFactory build(InputStream inputStream) {
            return this.build((InputStream)inputStream, (String)null, (Properties)null);
        }
        
    	public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
            SqlSessionFactory var5;
            try {
                //根据inputStream创建能解析该文件的XMLConfigBuilder解析器parser 
                XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
                //调用解析器parser 的parse()方法
                var5 = this.build(parser.parse());
            } catch (Exception var14) {
                throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
            } finally {
                ErrorContext.instance().reset();
                try {
                    inputStream.close();
                } catch (IOException var13) {
                    ;
                }
            }
            return var5;
        }

这块的parser 是一个XPthParser 。是一个基于dom4j的XPthParser 解析的工具。  
![在这里插入图片描述][20190426210800851.png]  
2、XMLConfigBuilder

public Configuration parse() {
            if (this.parsed) {
                throw new BuilderException("Each XMLConfigBuilder can only be used once.");
            } else {
                this.parsed = true;
                //调用parseConfiguration解析配置。this.parser.evalNode("/configuration")拿到configuration根节点
                this.parseConfiguration(this.parser.evalNode("/configuration"));
                return this.configuration;
            }
        }
        
        //拿到每个节点并解析值
        private void parseConfiguration(XNode root) {
            try {
                Properties settings = this.settingsAsPropertiess(root.evalNode("settings"));
                this.propertiesElement(root.evalNode("properties"));
                this.loadCustomVfs(settings);
                this.typeAliasesElement(root.evalNode("typeAliases"));
                this.pluginElement(root.evalNode("plugins"));
                this.objectFactoryElement(root.evalNode("objectFactory"));
                this.objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
                this.reflectorFactoryElement(root.evalNode("reflectorFactory"));
                //解析settings标签。把settings标签里面的配置保存成一个configuration
                this.settingsElement(settings);  
                this.environmentsElement(root.evalNode("environments"));
                this.databaseIdProviderElement(root.evalNode("databaseIdProvider"));
                this.typeHandlerElement(root.evalNode("typeHandlers"));
                //解析mapper标签
                this.mapperElement(root.evalNode("mappers"));
            } catch (Exception var3) {
                throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + var3, var3);
            }
        }
        
        //解析每一个配置的内容并保存在configuration中。里面的true和false是配置的默认值
    	private void settingsElement(Properties props) throws Exception {
            this.configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
            this.configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));
            this.configuration.setCacheEnabled(this.booleanValueOf(props.getProperty("cacheEnabled"), true));
            this.configuration.setProxyFactory((ProxyFactory)this.createInstance(props.getProperty("proxyFactory")));
            this.configuration.setLazyLoadingEnabled(this.booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));
            this.configuration.setAggressiveLazyLoading(this.booleanValueOf(props.getProperty("aggressiveLazyLoading"), true));
            this.configuration.setMultipleResultSetsEnabled(this.booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
            this.configuration.setUseColumnLabel(this.booleanValueOf(props.getProperty("useColumnLabel"), true));
            this.configuration.setUseGeneratedKeys(this.booleanValueOf(props.getProperty("useGeneratedKeys"), false));
            this.configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
            this.configuration.setDefaultStatementTimeout(this.integerValueOf(props.getProperty("defaultStatementTimeout"), (Integer)null));
            this.configuration.setDefaultFetchSize(this.integerValueOf(props.getProperty("defaultFetchSize"), (Integer)null));
            this.configuration.setMapUnderscoreToCamelCase(this.booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
            this.configuration.setSafeRowBoundsEnabled(this.booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
            this.configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
            this.configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
            this.configuration.setLazyLoadTriggerMethods(this.stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
            this.configuration.setSafeResultHandlerEnabled(this.booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
            this.configuration.setDefaultScriptingLanguage(this.resolveClass(props.getProperty("defaultScriptingLanguage")));
            this.configuration.setCallSettersOnNulls(this.booleanValueOf(props.getProperty("callSettersOnNulls"), false));
            this.configuration.setUseActualParamName(this.booleanValueOf(props.getProperty("useActualParamName"), false));
            this.configuration.setLogPrefix(props.getProperty("logPrefix"));
            Class<? extends Log> logImpl = this.resolveClass(props.getProperty("logImpl"));
            this.configuration.setLogImpl(logImpl);
            this.configuration.setConfigurationFactory(this.resolveClass(props.getProperty("configurationFactory")));
        }
       
        private void mapperElement(XNode parent) throws Exception {
            if (parent != null) {
                Iterator i$ = parent.getChildren().iterator();
    
                while(true) {
                    while(i$.hasNext()) {
                        XNode child = (XNode)i$.next();
                        String resource;
                        //package标签
                        if ("package".equals(child.getName())) {
                            resource = child.getStringAttribute("name");
                            this.configuration.addMappers(resource);
                        } else {
                        	//获取resource属性值
                            resource = child.getStringAttribute("resource");
                            //获取url属性值
                            String url = child.getStringAttribute("url");
                            //获取class属性值
                            String mapperClass = child.getStringAttribute("class");
                            XMLMapperBuilder mapperParser;
                            InputStream inputStream;
                            if (resource != null && url == null && mapperClass == null) {
                                ErrorContext.instance().resource(resource);
                                inputStream = Resources.getResourceAsStream(resource);
                                //创建XMLMapperBuilder 的解析器mapperParser 
                                mapperParser = new XMLMapperBuilder(inputStream, this.configuration, resource, this.configuration.getSqlFragments());
                                //解析mapper.xml文件
                                mapperParser.parse();
                            } else if (resource == null && url != null && mapperClass == null) {
                                ErrorContext.instance().resource(url);
                                inputStream = Resources.getUrlAsStream(url);
                                mapperParser = new XMLMapperBuilder(inputStream, this.configuration, url, this.configuration.getSqlFragments());
                                mapperParser.parse();
                            } else {
                                if (resource != null || url != null || mapperClass == null) {
                                    throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
                                }
    
                                Class<?> mapperInterface = Resources.classForName(mapperClass);
                                this.configuration.addMapper(mapperInterface);
                            }
                        }
                    }
    
                    return;
                }
            }
        }

3、XMLMapperBuilder

public void parse() {
            if (!this.configuration.isResourceLoaded(this.resource)) {
            	//解析mapper节点下的元素
                this.configurationElement(this.parser.evalNode("/mapper"));
                this.configuration.addLoadedResource(this.resource);
                this.bindMapperForNamespace();
            }
    
            this.parsePendingResultMaps();
            this.parsePendingChacheRefs();
            this.parsePendingStatements();
        }
        
        //解析mapper.xml的各个标签
        private void configurationElement(XNode context) {
            try {
                String namespace = context.getStringAttribute("namespace");
                if (namespace != null && !namespace.equals("")) {
                    this.builderAssistant.setCurrentNamespace(namespace);
                    this.cacheRefElement(context.evalNode("cache-ref"));
                    this.cacheElement(context.evalNode("cache"));
                    this.parameterMapElement(context.evalNodes("/mapper/parameterMap"));
                    this.resultMapElements(context.evalNodes("/mapper/resultMap"));
                    this.sqlElement(context.evalNodes("/mapper/sql"));
                    //解析select|insert|update|delete增删改查标签
                    this.buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
                } else {
                    throw new BuilderException("Mapper's namespace cannot be empty");
                }
            } catch (Exception var3) {
                throw new BuilderException("Error parsing Mapper XML. Cause: " + var3, var3);
            }
        }
        
    	//拿到select|insert|update|delete所有标签
    	public List<XNode> evalNodes(String expression) {
            return this.xpathParser.evalNodes(this.node, expression);
        }
        
     	private void buildStatementFromContext(List<XNode> list) {
            if (this.configuration.getDatabaseId() != null) {
                this.buildStatementFromContext(list, this.configuration.getDatabaseId());
            }
    
            this.buildStatementFromContext(list, (String)null);
        }
        
        private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
            Iterator i$ = list.iterator();
    
            while(i$.hasNext()) {
                XNode context = (XNode)i$.next();
                //创建能解析增删改查的XMLStatementBuilder 的解析器statementParser 
                XMLStatementBuilder statementParser = new XMLStatementBuilder(this.configuration, this.builderAssistant, context, requiredDatabaseId);
                try {
                	//用statementParser 解析StatementNode。StatementNode就是sql语句节点，即增删改查节点
                    statementParser.parseStatementNode();
                } catch (IncompleteElementException var7) {
                    this.configuration.addIncompleteStatement(statementParser);
                }
            }
    
        }

4、XMLStatementBuilder

//解析增删改查标签的详细信息
        public void parseStatementNode() {
            String id = this.context.getStringAttribute("id");
            String databaseId = this.context.getStringAttribute("databaseId");
            if (this.databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
                Integer fetchSize = this.context.getIntAttribute("fetchSize");
                Integer timeout = this.context.getIntAttribute("timeout");
                String parameterMap = this.context.getStringAttribute("parameterMap");
                String parameterType = this.context.getStringAttribute("parameterType");
                Class<?> parameterTypeClass = this.resolveClass(parameterType);
                String resultMap = this.context.getStringAttribute("resultMap");
                String resultType = this.context.getStringAttribute("resultType");
                String lang = this.context.getStringAttribute("lang");
                LanguageDriver langDriver = this.getLanguageDriver(lang);
                Class<?> resultTypeClass = this.resolveClass(resultType);
                String resultSetType = this.context.getStringAttribute("resultSetType");
                StatementType statementType = StatementType.valueOf(this.context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
                ResultSetType resultSetTypeEnum = this.resolveResultSetType(resultSetType);
                String nodeName = this.context.getNode().getNodeName();
                SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
                boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
                boolean flushCache = this.context.getBooleanAttribute("flushCache", !isSelect);
                boolean useCache = this.context.getBooleanAttribute("useCache", isSelect);
                boolean resultOrdered = this.context.getBooleanAttribute("resultOrdered", false);
                XMLIncludeTransformer includeParser = new XMLIncludeTransformer(this.configuration, this.builderAssistant);
                includeParser.applyIncludes(this.context.getNode());
                this.processSelectKeyNodes(id, parameterTypeClass, langDriver);
                SqlSource sqlSource = langDriver.createSqlSource(this.configuration, this.context, parameterTypeClass);
                String resultSets = this.context.getStringAttribute("resultSets");
                String keyProperty = this.context.getStringAttribute("keyProperty");
                String keyColumn = this.context.getStringAttribute("keyColumn");
                String keyStatementId = id + "!selectKey";
                keyStatementId = this.builderAssistant.applyCurrentNamespace(keyStatementId, true);
                Object keyGenerator;
                if (this.configuration.hasKeyGenerator(keyStatementId)) {
                    keyGenerator = this.configuration.getKeyGenerator(keyStatementId);
                } else {
                    keyGenerator = this.context.getBooleanAttribute("useGeneratedKeys", this.configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType)) ? new Jdbc3KeyGenerator() : new NoKeyGenerator();
                }
    			//调用addMappedStatement方法将解析到的增删改查标签的详细信息封装成一个MappedStatement
                this.builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType, fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass, resultSetTypeEnum, flushCache, useCache, resultOrdered, (KeyGenerator)keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
            }
        }

5、MapperBuilderAssistant

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 (this.unresolvedCacheRef) {
                throw new IncompleteElementException("Cache-ref not yet resolved");
            } else {
                id = this.applyCurrentNamespace(id, false);
                boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
                org.apache.ibatis.mapping.MappedStatement.Builder statementBuilder = (new org.apache.ibatis.mapping.MappedStatement.Builder(this.configuration, id, sqlSource, sqlCommandType)).resource(this.resource).fetchSize(fetchSize).timeout(timeout).statementType(statementType).keyGenerator(keyGenerator).keyProperty(keyProperty).keyColumn(keyColumn).databaseId(databaseId).lang(lang).resultOrdered(resultOrdered).resultSets(resultSets).resultMaps(this.getStatementResultMaps(resultMap, resultType, id)).resultSetType(resultSetType).flushCacheRequired((Boolean)this.valueOrDefault(flushCache, !isSelect)).useCache((Boolean)this.valueOrDefault(useCache, isSelect)).cache(this.currentCache);
                ParameterMap statementParameterMap = this.getStatementParameterMap(parameterMap, parameterType, id);
                if (statementParameterMap != null) {
                    statementBuilder.parameterMap(statementParameterMap);
                }
    			//调用statementBuilder的build方法构建MappedStatement 
                MappedStatement statement = statementBuilder.build();
                //MappedStatement 保存到configuration中
                this.configuration.addMappedStatement(statement);
                return statement;
            }
        }

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