MybatisSqlSessionFactoryBuilder源码的示例 分析

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。

一：源码分析代码片段

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();    }}

首先对步骤2进行分析

// 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：

第三步源码分析

// 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：

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：

                    select * from user where id=#{id}    

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 sqlFragments) {    this(new XPathParser(inputStream, true, configuration.getVariables(), new XMLMapperEntityResolver()), configuration, resource, sqlFragments);}private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map 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 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  void addMapper(Class type) {    this.mapperRegistry.addMapper(type);}

public  void addMapper(Class 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, 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：

总结:

1. 获取本地InputStreamReader对象（mybatis配置文件）

2. 调用SqlSessionFactoryBuilder

3. ###再使用XMLConfigBuilder解析mybatis配置文件，装配到Configuration中。

4. 将配置文件中的Mapper添加到Configuration mapperRegistry实现注册。

5. 备注：mapperRegistry存放当前所有的mapper接口。

6. loadedResources里面的东西：存放的是userMapper的配置文件

看完上述内容是否对您有帮助呢？如果还想对相关知识有进一步的了解或阅读更多相关文章，请关注行业资讯频道，感谢您对的支持。