网站流量多少做网盟,工程招标平台,网站建设全视频教程下载,网站建设交易SqlSessionFactoryBuilder.build创建SqlSessionFactory#xff08;粗略走一步流程#xff09; 看完上篇文章后#xff0c;你对mybatis应该有个大概的了解了#xff0c;那么我们知道new SqlSessionFactoryBuilder().build是框架的入口#xff0c;我们到SqlSessionFactoryB…SqlSessionFactoryBuilder.build创建SqlSessionFactory粗略走一步流程 看完上篇文章后你对mybatis应该有个大概的了解了那么我们知道new SqlSessionFactoryBuilder().build是框架的入口我们到SqlSessionFactoryBuilder类里看到里面其实都是build函数的。 全都是build重载函数。上面几个重载其实最终都是调用了build(Reader reader, String environment, Properties properties)这个方法。下面的几个则是调用了build(InputStream inputStream, String environment, Properties properties) 。 最终都会调用最后一个build(Configuration config)方法把创建好的Configuration赋给DefaultSqlSessionFactory里面的Configuration字段所以这里的逻辑其实非常简单就是解析传入配置文件的Reader或者inputStream然后生成Configuration赋值给新建出来的DefaultSqlSessionFactor中的configuration字段然后返回DefaultSqlSessionFactor。 public class SqlSessionFactoryBuilder {public SqlSessionFactory build(Reader reader) {return build(reader, null, null);}public SqlSessionFactory build(Reader reader, String environment) {return build(reader, environment, null);}public SqlSessionFactory build(Reader reader, Properties properties) {return build(reader, null, properties);}public SqlSessionFactory build(Reader reader, String environment, Properties properties) {try {XMLConfigBuilder parser new XMLConfigBuilder(reader, environment, properties);return build(parser.parse());} catch (Exception e) {throw ExceptionFactory.wrapException(Error building SqlSession., e);} finally {ErrorContext.instance().reset();try {reader.close();} catch (IOException e) {// Intentionally ignore. Prefer previous error.}}}public SqlSessionFactory build(InputStream inputStream) {return build(inputStream, null, null);}public SqlSessionFactory build(InputStream inputStream, String environment) {return build(inputStream, environment, null);}public SqlSessionFactory build(InputStream inputStream, Properties properties) {return build(inputStream, null, properties);}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);}}下面我们来完整的走一个流程就以上一篇的demo为例 //第一步public static SqlSession getSqlsession(){//获取mybatisconfig的xml文件的输入流InputStream config MybatisUtil.class.getClassLoader().getResourceAsStream(mybatis.cfg.xml);//使用SqlSessionFactory build(InputStream inputStream)来获取SqlSessionFactorySqlSessionFactory build new SqlSessionFactoryBuilder().build(config);return build.openSession();}//第二步调用SqlSessionFactoryBuilder中的build(InputStream inputStream)方法public SqlSessionFactory build(InputStream inputStream) {return build(inputStream, null, null);}//第三部调用SqlSessionFactoryBuilder中的build(InputStream inputStream, String environment, Properties properties)方法public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {try {//把输入流解析成可以用做分析的document以及准备其他解析需要的东西XMLConfigBuilder parser new XMLConfigBuilder(inputStream, environment, properties);//parser.parse()生成出Configuration类最后调用build(Configuration config)方法来生成DefaultSqlSessionFactory并返回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.}}}//第四步调用SqlSessionFactoryBuilder中的 build(Configuration config) 方法public SqlSessionFactory build(Configuration config) {return new DefaultSqlSessionFactory(config);}这是最上面的一层逻辑还是非常简单的一句话就能概括就是从给定的配置文件中解析出Configuration然后生成DefaultSqlSessionFactory。如果要指定环境和特定的属性的话用另外2个build 的重载方法 我们先进入最后一个build看一下new DefaultSqlSessionFactory(config);究竟做了什么。 public class DefaultSqlSessionFactory implements SqlSessionFactory {private final Configuration configuration;public DefaultSqlSessionFactory(Configuration configuration) {//非常简单就是生成了一个DefaultSqlSessionFactory 类然后把里面的configuration字段赋值为传入的configuration。this.configuration configuration;}//后面的函数就不列出来了}build是如何通过xml文件来生成Configuration的比较详细的分析流程 所以build的重点在解析xml成Configuration 类这个地方。 也就是下面这两句话 XMLConfigBuilder parser new XMLConfigBuilder(inputStream, environment, properties);parser.parse();ok第一句话是生成了一个XMLConfigBuilder类我们来看看XMLConfigBuilder到底是什么样的。只列出字段和关键方法 public class XMLConfigBuilder extends BaseBuilder {private boolean parsed;private XPathParser parser;private String environment;private ReflectorFactory localReflectorFactory new DefaultReflectorFactory();//上层调用到这个方法然后他调用到了下面的重载方法public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {//这里只有new XPathParser(inputStream, true, props, new XMLMapperEntityResolver())需要看一下this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);}//其实就是给关键的几个字段赋值这里的第一句调用了父类的构造函数传入了一个新的Configuration也就是说到这步的时候我们用来返回的Configuration对象已经有了但是Configuration的值还没有构造好。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;}}public abstract class BaseBuilder {protected final Configuration configuration;protected final TypeAliasRegistry typeAliasRegistry;protected final TypeHandlerRegistry typeHandlerRegistry;}接下来我们来看看XPathParser类 public class XPathParser {private Document document;private boolean validation;private EntityResolver entityResolver;private Properties variables;private XPath xpath;public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) {//为类的其他字段赋值commonConstructor(validation, variables, entityResolver);//根据输入流创建一个Document 并赋值给 document字段之后的解析就靠这里面的信息了this.document createDocument(new InputSource(inputStream));}}xml解析成Document的具体过程LZ就不带大家深入研究了有兴趣的朋友可以自己跟下去看看。 接下来我们回到SqlSessionFactoryBuilder类。 public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {//现在我们已经拿到parser了XMLConfigBuilder parser new XMLConfigBuilder(inputStream, environment, properties);//接下来要去看parse()是怎么创建出Configuration的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 Configuration parse() {if (parsed) {throw new BuilderException(Each XMLConfigBuilder can only be used once.);}parsed true;//解析靠这步首先拿到configuration节点parseConfiguration(parser.evalNode(/configuration));return configuration;}public XNode evalNode(String expression) {return evalNode(document, expression);}public XNode evalNode(Object root, String expression) {//拿到configuration节点Node node (Node) evaluate(expression, root, XPathConstants.NODE);if (node null) {return null;}//返回封装成XNode类return new XNode(this, node, variables);} public class XNode {private Node node;private String name;private String body;private Properties attributes;private Properties variables;private XPathParser xpathParser;public XNode(XPathParser xpathParser, Node node, Properties variables) {this.xpathParser xpathParser;this.node node;this.name node.getNodeName();this.variables variables;this.attributes parseAttributes(node);this.body parseBody(node);} }XPathParser类的实际值 封装好的Xnode的实际值 //接下来就要解析并给configuration赋值拉。因为configuration在新建XMLConfigBuilder的时候就已经创建好了解析的过程其实就是赋值的过程我们在xml文件里配置的各个节点都在下面这个函数里解析 private void parseConfiguration(XNode root) {try {//issue #117 read properties firstpropertiesElement(root.evalNode(properties));Properties settings settingsAsProperties(root.evalNode(settings));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);}}这是xml文件中要的标签和上面代码一对比你就会清楚的明白上面每一个方法其实就是把每一个标签转换成configuration。 private void propertiesElement(XNode context) throws Exception {if (context ! null) {//从子属性直接获取属性的键值对Properties defaults context.getChildrenAsProperties();//从外部引入属性文件其实就是获取resource属性的值String resource context.getStringAttribute(resource);//也可以从url下获取属性文件引入网络路径或者磁盘路径下的资源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.);}//从resource 或者 url的属性文件中加载键值对若和上面的defaults键相同则替换defaults中的if (resource ! null) {defaults.putAll(Resources.getResourceAsProperties(resource));} else if (url ! null) {defaults.putAll(Resources.getUrlAsProperties(url));}Properties vars configuration.getVariables();if (vars ! null) {defaults.putAll(vars);}//设置parser的Variablesparser.setVariables(defaults);//设置configuration的Variablesconfiguration.setVariables(defaults);}} 其他的解析其实和properties的解析差不多。根据配置文件节点的信息设置configuration。 因为mybatis非常重要的一个点就是在mapper上所以楼主之后会有一篇专门写mapper是什么解析和使用的。所以这里大家可以简单过一下mapper的解析过程。 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) { //根据resource解析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) {//根据url 解析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) {//根据mapperClass解析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.);}}}}}套路其实差不多就不细细的深入看了。但是mybatis的mapper的实现方法还是要细细讨论的让我们在之后的文章中在细致的学习以下。 小结 看了加载过程的源码我们在这至少了解到了mybatis是如何解析xml文件的还有properties假如我们即在xml文件中直接配置的属性和又设置了resource或者url的话resource或者url中的属性会覆盖xml文件中直接配的key相同的情况下才会覆盖否则是累加的情况若详细看过mapper的创建过程的话还会知道在xml中配的mapper的语句会被注解中配置的语句覆盖。为什么会有这些特性因为源码的读取步骤以及策略如此所以要善于利用