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MybatisSqlSessionFactoryBuilder源码的示例 分析,很多新手对此不是很清楚,为了帮助大家解决这个难题,下面小编将为大家详细讲解,有这方面需求的人可以来学习下,希望你能有所收获。
public static void main(String[] args) { try { // 基本mybatis环境 // 1.定义mybatis_config文件地址 String resources = "mybatis_config.xml"; // 2.获取InputStreamReaderIo流 Reader reader = Resources.getResourceAsReader(resources); // 3.获取SqlSessionFactory SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader); // 4.获取Session SqlSession sqlSession = sqlSessionFactory.openSession(); // 5.操作Mapper接口 UserMapper mapper = sqlSession.getMapper(UserMapper.class); UserEntity user = mapper.getUser(2); System.out.println(user.getName()); } catch (Exception e) { e.printStackTrace(); } }
// 2.获取InputStreamReaderIo流
Reader reader = Resources.getResourceAsReader(resources);
public static Reader getResourceAsReader(String resource) throws IOException { InputStreamReader reader; if (charset == null) { reader = new InputStreamReader(getResourceAsStream(resource)); } else { reader = new InputStreamReader(getResourceAsStream(resource), charset); } return reader; }
通过上述代码可知:使用了门面模式:定义了Resource类,把复杂过程封装起来,方便用户使用,返回reader为InputStreamReader,指的是读取的mybatis_config.xml文件,断点调试结果如下:
// 3.获取SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
进入SqlSessionFactoryBuilder()构造函数如下:
public SqlSessionFactoryBuilder() { }
可知,无参构造函数没用做任何事情,再进入build(reader)源码,reader参数为InputStream流
public SqlSessionFactory build(Reader reader) { return this.build((Reader)reader, (String)null, (Properties)null); }
public SqlSessionFactory build(Reader reader, String environment, Properties properties) { SqlSessionFactory var5; try { XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties); var5 = this.build(parser.parse()); } catch (Exception var14) { throw ExceptionFactory.wrapException("Error building SqlSession.", var14); } finally { ErrorContext.instance().reset(); try { reader.close(); } catch (IOException var13) { ; } } return var5; }
我们来分析下XMLConfigBuilder这个类是干嘛的,进入XMLConfigBuilder构造函数如下:
public XMLConfigBuilder(Reader reader, String environment, Properties props) { this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props); }
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) { super(new Configuration()); this.localReflectorFactory = new DefaultReflectorFactory(); ErrorContext.instance().resource("SQL Mapper Configuration"); this.configuration.setVariables(props); this.parsed = false; this.environment = environment; this.parser = parser; }
进入super()代码如下:
public BaseBuilder(Configuration configuration) { this.configuration = configuration; this.typeAliasRegistry = this.configuration.getTypeAliasRegistry(); this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry(); }
通过上述代码可知:this.parsed = false;后面有用,这里先提下。返回原先执行处:var5 = this.build(parser.parse());
var5 = this.build(parser.parse());
进入parser.parse()这个方法,代码如下:
public Configuration parse() { if (this.parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } else { this.parsed = true; this.parseConfiguration(this.parser.evalNode("/configuration")); return this.configuration; } }
由前面设置了this.parsed = false,可知this.parsed为false,就进入else分支,读者这个时候就有疑问了,为啥要设置this.parsed = false呢?
我们通过else分支可知,又设置了 this.parsed = true;说明再下一次再次进入parse方法的时候,this.parsed=true会直接抛出异常。
这里我们可以总结下:
为什么XMLConfigBuilder只能被使用一次呢?
答:因为我们的Configuration是一个全局的,所以只能被解析一次。
多次解析的话,会抛出:Each XMLConfigBuilder can only be used once.异常,防止用户私自调用parse()方法再去重复解析,因为配置文件是全局的,不能多次解析。
进入else分支的下面这个代码中:
this.parseConfiguration(this.parser.evalNode("/configuration"));
private void parseConfiguration(XNode root) { try { this.propertiesElement(root.evalNode("properties")); this.typeAliasesElement(root.evalNode("typeAliases")); this.pluginElement(root.evalNode("plugins")); this.objectFactoryElement(root.evalNode("objectFactory")); this.objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); this.reflectionFactoryElement(root.evalNode("reflectionFactory")); this.settingsElement(root.evalNode("settings")); this.environmentsElement(root.evalNode("environments")); this.databaseIdProviderElement(root.evalNode("databaseIdProvider")); this.typeHandlerElement(root.evalNode("typeHandlers")); this.mapperElement(root.evalNode("mappers")); } catch (Exception var3) { throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + var3, var3); } }
我们先看看mybatis_config.xml配置文件的内容:
<configuration> <!-- 环境配置 --> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <!-- 数据库连接相关配置 ,这里动态获取config.properties文件中的内容--> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/test"/> <property name="username" value="root"/> <property name="password" value="root"/> </dataSource> </environment> </environments> <!-- mapping文件路径配置 --> <mappers> <mapper resource="mappers/UserMapper.xml"/> </mappers> </configuration>
我们先进入下面这行代码:因为这个environments在我们配置文件中配置了,我们先分析它:
this.environmentsElement(root.evalNode("environments"))
private void environmentsElement(XNode context) throws Exception { if (context != null) { if (this.environment == null) { this.environment = context.getStringAttribute("default"); } Iterator i$ = context.getChildren().iterator(); while(i$.hasNext()) { XNode child = (XNode)i$.next(); String id = child.getStringAttribute("id"); if (this.isSpecifiedEnvironment(id)) { TransactionFactory txFactory = this.transactionManagerElement(child.evalNode("transactionManager")); DataSourceFactory dsFactory = this.dataSourceElement(child.evalNode("dataSource")); DataSource dataSource = dsFactory.getDataSource(); Builder environmentBuilder = (new Builder(id)).transactionFactory(txFactory).dataSource(dataSource); this.configuration.setEnvironment(environmentBuilder.build()); } } } }
通过断点调试environmentsElement()代码结果如下:
我们看下这段代码:
this.configuration.setEnvironment(environmentBuilder.build());
public void setEnvironment(Environment environment) { this.environment = environment; }
到这里我们就明白了:这里将解析的XML结点封装成Environment对象,再把Environment对象设置给Configuration对象中。也就是解析XML,再把XML转为Configuration实体类
到这里我们再来分析:mappers结点在配置文件中配置了,我们也来分析下,下面是mapper.xml配置文件的内容,看下是如何转化为实体对象保存起来的:
<mapper namespace="com.mayikt.mapper.UserMapper"> <!-- 在select标签中编写查询的SQL语句, 设置select标签的id属性为getUser,id属性值必须是唯一的,不能够重复 使用parameterType属性指明查询时使用的参数类型,resultType属性指明查询返回的结果集类型 resultType="com.mayikt.entity.User"就表示将查询结果封装成一个User类的对象返回 User类就是users表所对应的实体类 --> <!-- 根据id查询得到一个user对象 --> <select id="getUser" parameterType="int" resultType="com.mayikt.entity.UserEntity"> select * from user where id=#{id} </select> </mapper>
this.mapperElement(root.evalNode("mappers"));
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; if ("package".equals(child.getName())) { //注解方式配置扫包package resource = child.getStringAttribute("name"); this.configuration.addMappers(resource); } else { //resource 方式 resource = child.getStringAttribute("resource"); String url = child.getStringAttribute("url"); String mapperClass = child.getStringAttribute("class"); XMLMapperBuilder mapperParser; InputStream inputStream; if (resource != null && url == null && mapperClass == null) { ErrorContext.instance().resource(resource); inputStream = Resources.getResourceAsStream(resource); mapperParser = new XMLMapperBuilder(inputStream, this.configuration, resource, this.configuration.getSqlFragments()); 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; } } }
通过上述代码可知,配置方式有两种:一种是注解形式扫包,第二种是resource方式
我们是resource方式的配置,所以进入else分支:
由上面断点分析可知,这里会读取mapper.xml配置文件的内容,转化为inputStream流,再解析mapper.xml配置文件
XMLMapperBuilder类的作用:解析mapper配置文件得到Configuration对象,我们看下XMLMapperBuilder怎么去解析mapper配置文件
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; }
最终进入:
mapperParser.parse()
public void parse() { if (!this.configuration.isResourceLoaded(this.resource)) { this.configurationElement(this.parser.evalNode("/mapper")); this.configuration.addLoadedResource(this.resource); this.bindMapperForNamespace(); }
进入addLoadedResource()方法:
public void addLoadedResource(String resource) { this.loadedResources.add(resource); }
protected final Set<String> loadedResources;
public Configuration() { this.loadedResources = new HashSet(); }
通过上述代码可知:loadedResources存放的都是mybatis映射的文件路径地址【mapper.xml】, 使用HashSet集合存放
存放进去之后,断点如下:
我们进入下面这个方法:
this.bindMapperForNamespace();
private void bindMapperForNamespace() { String namespace = this.builderAssistant.getCurrentNamespace(); //拿到mapper.xml里面配置的namespace,这里是com.mayikt.mapper.UserMapper if (namespace != null) { Class boundType = null; try { boundType = Resources.classForName(namespace); //通过Java反射机制帮我去查找,这里得到interface com.mayikt.mapper.UserMapper } catch (ClassNotFoundException var4) { ; } if (boundType != null && !this.configuration.hasMapper(boundType)) {//判断mapper.xml配置文件是否注册过 this.configuration.addLoadedResource("namespace:" + namespace); this.configuration.addMapper(boundType); } } }
先看看addMapper方法:
this.configuration.addMapper(boundType);
public <T> void addMapper(Class<T> type) { this.mapperRegistry.addMapper(type); }
public <T> void addMapper(Class<T> type) { if (type.isInterface()) { //判断是否是接口类型 if (this.hasMapper(type)) { //再次判断是否注册过,如果注册过,则抛出异常 throw new BindingException("Type " + type + " is already known to the MapperRegistry."); } boolean loadCompleted = false; try { this.knownMappers.put(type, new MapperProxyFactory(type)); MapperAnnotationBuilder parser = new MapperAnnotationBuilder(this.config, type); parser.parse(); loadCompleted = true; } finally { if (!loadCompleted) { this.knownMappers.remove(type); } } }
this.knownMappers.put(type, new MapperProxyFactory(type));
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap();
由上述代码可知:mapperRegistry作用是:存放dao层mapper接口,debug结果如下:
最后,我们来看看loadedResources里面的东西:存放的是userMapper的配置文件
再看看mapperRegistery里面的东西:存放的是mapper接口
最后,我们回到开始的parse()方法,上述代码执行完this.parseConfiguration(this.parser.evalNode("/configuration"))方法之后,返回configuration对象
public Configuration parse() { if (this.parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } else { this.parsed = true; this.parseConfiguration(this.parser.evalNode("/configuration")); return this.configuration; } }
到这里,我们就结束了源码分析,下面总结下大体流程:
获取本地InputStreamReader对象(mybatis配置文件)
调用SqlSessionFactoryBuilder
###再使用XMLConfigBuilder解析mybatis配置文件,装配到Configuration中。
将配置文件中的Mapper添加到Configuration mapperRegistry实现注册。
备注:mapperRegistry存放当前所有的mapper接口。
loadedResources里面的东西:存放的是userMapper的配置文件
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