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MybatisSqlSessionFactoryBuilder源碼的示例 分析，很多新手對此不是很清楚，為了幫助大家解決這個難題，下面小編將為大家詳細講解，有這方面需求的人可以來學習下，希望你能有所收獲。
public static void main(String[] args) {
try {
// 基本mybatis環境
// 1.定義mybatis_config文件地址
String resources = "mybatis_config.xml";
// 2.獲取InputStreamReaderIo流
Reader reader = Resources.getResourceAsReader(resources);
// 3.獲取SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
// 4.獲取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.獲取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;
}通過上述代碼可知：使用了門面模式：定義了Resource類，把復雜過程封裝起來，方便用戶使用，返回reader為InputStreamReader，指的是讀取的mybatis_config.xml文件，斷點調試結果如下：
// 3.獲取SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
進入SqlSessionFactoryBuilder（）構造函數如下：
public SqlSessionFactoryBuilder() {
}可知，無參構造函數沒用做任何事情，再進入build(reader)源碼，reader參數為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;
}我們來分析下XMLConfigBuilder這個類是干嘛的，進入XMLConfigBuilder構造函數如下：
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;
}進入super()代碼如下：
public BaseBuilder(Configuration configuration) {
this.configuration = configuration;
this.typeAliasRegistry = this.configuration.getTypeAliasRegistry();
this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry();
}通過上述代碼可知：this.parsed = false;后面有用，這里先提下。返回原先執行處：var5 = this.build(parser.parse());
var5 = this.build(parser.parse());
進入parser.parse()這個方法，代碼如下：
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;
}
}由前面設置了this.parsed = false，可知this.parsed為false，就進入else分支，讀者這個時候就有疑問了，為啥要設置this.parsed = false呢？
我們通過else分支可知，又設置了 this.parsed = true;說明再下一次再次進入parse方法的時候，this.parsed=true會直接拋出異常。
這里我們可以總結下：
為什么XMLConfigBuilder只能被使用一次呢？
答：因為我們的Configuration是一個全局的，所以只能被解析一次。
多次解析的話，會拋出：Each XMLConfigBuilder can only be used once.異常，防止用戶私自調用parse（）方法再去重復解析，因為配置文件是全局的，不能多次解析。
進入else分支的下面這個代碼中：
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);
}
}我們先看看mybatis_config.xml配置文件的內容：
<configuration> <!-- 環境配置 --> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <!-- 數據庫連接相關配置 ,這里動態獲取config.properties文件中的內容--> <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文件路徑配置 --> <mappers> <mapper resource="mappers/UserMapper.xml"/> </mappers> </configuration>
我們先進入下面這行代碼：因為這個environments在我們配置文件中配置了，我們先分析它：
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());
}
}
}
}通過斷點調試environmentsElement（）代碼結果如下：
我們看下這段代碼：
this.configuration.setEnvironment(environmentBuilder.build());
public void setEnvironment(Environment environment) {
this.environment = environment;
}
到這里我們就明白了：這里將解析的XML結點封裝成Environment對象，再把Environment對象設置給Configuration對象中。也就是解析XML,再把XML轉為Configuration實體類
到這里我們再來分析：mappers結點在配置文件中配置了，我們也來分析下,下面是mapper.xml配置文件的內容，看下是如何轉化為實體對象保存起來的：
<mapper namespace="com.mayikt.mapper.UserMapper">
<!-- 在select標簽中編寫查詢的SQL語句， 設置select標簽的id屬性為getUser，id屬性值必須是唯一的，不能夠重復
使用parameterType屬性指明查詢時使用的參數類型，resultType屬性指明查詢返回的結果集類型
resultType="com.mayikt.entity.User"就表示將查詢結果封裝成一個User類的對象返回
User類就是users表所對應的實體類
-->
<!--
根據id查詢得到一個user對象
-->
<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())) { //注解方式配置掃包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;
}
}
}通過上述代碼可知，配置方式有兩種：一種是注解形式掃包，第二種是resource方式
我們是resource方式的配置，所以進入else分支：
由上面斷點分析可知，這里會讀取mapper.xml配置文件的內容，轉化為inputStream流，再解析mapper.xml配置文件
XMLMapperBuilder類的作用：解析mapper配置文件得到Configuration對象，我們看下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;
}最終進入：
mapperParser.parse()
public void parse() {
if (!this.configuration.isResourceLoaded(this.resource)) {
this.configurationElement(this.parser.evalNode("/mapper"));
this.configuration.addLoadedResource(this.resource);
this.bindMapperForNamespace();
}進入addLoadedResource（）方法：
public void addLoadedResource(String resource) {
this.loadedResources.add(resource);
}protected final Set<String> loadedResources;
public Configuration() {
this.loadedResources = new HashSet();
}通過上述代碼可知：loadedResources存放的都是mybatis映射的文件路徑地址【mapper.xml】， 使用HashSet集合存放
存放進去之后，斷點如下：
我們進入下面這個方法：
this.bindMapperForNamespace();
private void bindMapperForNamespace() {
String namespace = this.builderAssistant.getCurrentNamespace(); //拿到mapper.xml里面配置的namespace，這里是com.mayikt.mapper.UserMapper
if (namespace != null) {
Class boundType = null;
try {
boundType = Resources.classForName(namespace); //通過Java反射機制幫我去查找，這里得到interface com.mayikt.mapper.UserMapper
} catch (ClassNotFoundException var4) {
;
}
if (boundType != null && !this.configuration.hasMapper(boundType)) {//判斷mapper.xml配置文件是否注冊過
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()) { //判斷是否是接口類型
if (this.hasMapper(type)) { //再次判斷是否注冊過，如果注冊過，則拋出異常
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();
由上述代碼可知：mapperRegistry作用是：存放dao層mapper接口，debug結果如下：
最后，我們來看看loadedResources里面的東西：存放的是userMapper的配置文件
再看看mapperRegistery里面的東西：存放的是mapper接口
最后，我們回到開始的parse（）方法，上述代碼執行完this.parseConfiguration(this.parser.evalNode("/configuration"))方法之后，返回configuration對象
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;
}
}到這里，我們就結束了源碼分析，下面總結下大體流程：
獲取本地InputStreamReader對象（mybatis配置文件）
調用SqlSessionFactoryBuilder
###再使用XMLConfigBuilder解析mybatis配置文件，裝配到Configuration中。
將配置文件中的Mapper添加到Configuration mapperRegistry實現注冊。
備注：mapperRegistry存放當前所有的mapper接口。
loadedResources里面的東西：存放的是userMapper的配置文件
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