Mybatis之Configuration初始化（配置文件.xml的解析）
源码解读第一步我觉着应该从Mybatis如何解析配置文件开始。
1.先不看跟Spring集成如何解析，先看从SqlSessionFactoryBuilder如果解析的。
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1 String resouce = "conf.xml";
2 InputStream is = Resources.getResourceAsStream(resouce);
3
4 // 构建sqlSession工厂
5 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
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SqlSessionFactoryBuilder
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1 public SqlSessionFactory build(InputStream inputStream) {
2 return build(inputStream, null, null);
3 }
4
5 public SqlSessionFactory build(InputStream inputStream, String environment) {
6 return build(inputStream, environment, null);
7 }
8
9 public SqlSessionFactory build(InputStream inputStream, Properties properties) {
10 return build(inputStream, null, properties);
11 }
12 //上面那么多同名不同参的方法最后都会进入这个方法
//支持传入Enviromment.properties实际上是支持动态传入覆盖全局配置xml的内容
13 public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
14 try {
15 XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
//因为从下面的Build方法可以看出 parser.parse()后Configuration就初始化好了
16 return build(parser.parse());
17 } catch (Exception e) {
18 throw ExceptionFactory.wrapException("Error building SqlSession.", e);
19 } finally {
20 ErrorContext.instance().reset();
21 try {
22 inputStream.close();
23 } catch (IOException e) {
24 // Intentionally ignore. Prefer previous error.
25 }
26 }
27 }
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
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真正初始化Configuration的类是XMLConfigBuilder
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1 public Configuration parse() {
//这一块可以看出来 全局Configuration只会初始化一次，实例化时候是false
2 if (parsed) {
3 throw new BuilderException("Each XMLConfigBuilder can only be used once.");
4 }
5 parsed = true;
6 parseConfiguration(parser.evalNode("/configuration"));
7 return configuration;
8 }
9 //获取配置文件整个/configuration节点内容
10 private void parseConfiguration(XNode root) {
11 try {
12 Properties settings = settingsAsPropertiess(root.evalNode("settings")); //初始化配置文件中全局变量
13 //issue #117 read properties first
14 propertiesElement(root.evalNode("properties"));//初始化xml中的配置文件，同时讲其中的变量保存起来，因为可能其他地方引用
15 loadCustomVfs(settings); //加载自定义的VFS实现类？ 这个什么用？
16 typeAliasesElement(root.evalNode("typeAliases")); //加载typeAliases别名初始化
17 pluginElement(root.evalNode("plugins")); //加载插件，实际上就是拦截器
18 objectFactoryElement(root.evalNode("objectFactory"));// //加载自定义的对象工厂
19 objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); //加载自定义的处理驼峰方式的key的处理器
20 reflectionFactoryElement(root.evalNode("reflectionFactory")); //加载自定义的反射器 没用过？
21 settingsElement(settings); //将setting的属性，设置到Configuration对象属性中
22 // read it after objectFactory and objectWrapperFactory issue #631
23 environmentsElement(root.evalNode("environments"));
24 databaseIdProviderElement(root.evalNode("databaseIdProvider"));
25 typeHandlerElement(root.evalNode("typeHandlers")); //初始化类型处理器
26 mapperElement(root.evalNode("mappers")); //处理mappers节点内容，实际上就是初始化MaperStatement
27 } catch (Exception e) {
28 throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
29 }
30 }
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因为大部分方法都比较简单，我这里只介绍几个我认为比较重要的。
① typeAliasesElement(root.evalNode("typeAliases")); //加载typeAliases别名初始化
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1 private void typeAliasesElement(XNode parent) {
2 if (parent != null) {
3 for (XNode child : parent.getChildren()) {
4 if ("package".equals(child.getName())) { //配置的是包名 扫描包里所有的类。放入的key默认是注解的key
5 String typeAliasPackage = child.getStringAttribute("name");
6 configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);
7 } else {
8 String alias = child.getStringAttribute("alias");
9 String type = child.getStringAttribute("type");
10 try {
11 Class clazz = Resources.classForName(type);
12 if (alias == null) {
13 typeAliasRegistry.registerAlias(clazz);
14 } else {
15 typeAliasRegistry.registerAlias(alias, clazz);
16 }
//实际上就是存在了TypeAliasRegistry类的一个私有map里面。
17 } catch (ClassNotFoundException e) {
18 throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e);
19 }
20 }
21 }
22 }
23 }
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1 public class TypeAliasRegistry {
2
3 private final Map> TYPE_ALIASES = new HashMap>();
。。。。。。
4 }
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② pluginElement(root.evalNode("plugins")); 加载插件，便于后期理解拦截器原理
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1 private void pluginElement(XNode parent) throws Exception {
2 if (parent != null) {
3 for (XNode child : parent.getChildren()) {
4 String interceptor = child.getStringAttribute("interceptor");
5 Properties properties = child.getChildrenAsProperties();
//获取interceptor 这里resolveClass实际上就是到TypeAliasResitstry里面找一下，找到了获取class,没有直接用class去反射回去对象
6 Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance();
7 interceptorInstance.setProperties(properties);
//获取对象后调用configuration方法。
8 configuration.addInterceptor(interceptorInstance);
9 }
10 }
11 }
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Configuration
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1 public void addInterceptor(Interceptor interceptor) {
2 interceptorChain.addInterceptor(interceptor);
3 }
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InterceptorChain
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1 public void addInterceptor(Interceptor interceptor) {
2 interceptors.add(interceptor);
3 }
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这一块就是放Configuration的拦截器链里面添加拦截器。这一块现在知道是在这时候添加的就好了。后面介绍Mybatis的拦截器的时候深入了解。
③ mapperElement(root.evalNode("mappers")); //处理mappers节点内容，实际上就是初始化MaperStatement
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1 private void mapperElement(XNode parent) throws Exception {
2 if (parent != null) {
3 for (XNode child : parent.getChildren()) {
4 if ("package".equals(child.getName())) {
5 String mapperPackage = child.getStringAttribute("name");
6 configuration.addMappers(mapperPackage);
7 } else {
8 String resource = child.getStringAttribute("resource");
9 String url = child.getStringAttribute("url");
10 String mapperClass = child.getStringAttribute("class");
//xml文件中mapper节点，配置resource,url是执行的mapper.xml文件的位置，所以现在只分析这一块。
11 if (resource != null && url == null && mapperClass == null) {
12 ErrorContext.instance().resource(resource);
13 InputStream inputStream = Resources.getResourceAsStream(resource);
14 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
15 mapperParser.parse();
16 } else if (resource == null && url != null && mapperClass == null) {
17 ErrorContext.instance().resource(url);
18 InputStream inputStream = Resources.getUrlAsStream(url);
19 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
20 mapperParser.parse();
21 } else if (resource == null && url == null && mapperClass != null) {
22 Class mapperInterface = Resources.classForName(mapperClass);
23 configuration.addMapper(mapperInterface);
24 } else {
25 throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
26 }
27 }
28 }
29 }
30 }
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可以看出来resource和url都是通过XMLMapperBuilder来解析的。下面来看下parse方法。
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1 private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map sqlFragments) {
2 super(configuration);
//前面还有个构造器，是根据传入的inputstream构造XPathParser,parser可以拿到resouce里面的内容
3 this.builderAssistant = new MapperBuilderAssistant(configuration, resource);
4 this.parser = parser;
5 this.sqlFragments = sqlFragments;
6 this.resource = resource;
7 }
8
9 public void parse() {
10 if (!configuration.isResourceLoaded(resource)) { 是否加载过改文件，
11 configurationElement(parser.evalNode("/mapper")); 来解析mapper文件内容
12 configuration.addLoadedResource(resource); 添加加载记录
13 bindMapperForNamespace();往configration添加命名空间的代理对象
14 }
15
16 parsePendingResultMaps();
17 parsePendingChacheRefs();
18 parsePendingStatements();
19 }
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1 private void configurationElement(XNode context) { //解析mapper.xml子节点的内容
2 try {
3 String namespace = context.getStringAttribute("namespace");
4 if (namespace == null || namespace.equals("")) {
5 throw new BuilderException("Mapper's namespace cannot be empty");
6 }
7 builderAssistant.setCurrentNamespace(namespace);
8 cacheRefElement(context.evalNode("cache-ref"));
9 cacheElement(context.evalNode("cache"));
10 parameterMapElement(context.evalNodes("/mapper/parameterMap"));
11 resultMapElements(context.evalNodes("/mapper/resultMap")); //解析resultMap 很复杂，后面单独解读
12 sqlElement(context.evalNodes("/mapper/sql"));
13 buildStatementFromContext(context.evalNodes("select|insert|update|delete")); //初始化这几个类型节点的内容
14 } catch (Exception e) {
15 throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
16 }
17 }
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1 private void buildStatementFromContext(List list) {
因为会有多个节点，所以是一个List
2 if (configuration.getDatabaseId() != null) {
3 buildStatementFromContext(list, configuration.getDatabaseId());
4 }
5 buildStatementFromContext(list, null);
6 }
7
8 private void buildStatementFromContext(List list, String requiredDatabaseId) {
9 for (XNode context : list) {
10 final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
11 try {
12 statementParser.parseStatementNode();
13 } catch (IncompleteElementException e) {
14 configuration.addIncompleteStatement(statementParser);
15 }
16 }
17 }
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从上面可以看出来最终是由XMLStatementBuilder来解析我们的写的sql部分。
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1 public void parseStatementNode() {
2 String id = context.getStringAttribute("id");
3 String databaseId = context.getStringAttribute("databaseId");
4
5 if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
6 return;
7 }
8
9 Integer fetchSize = context.getIntAttribute("fetchSize");
10 Integer timeout = context.getIntAttribute("timeout");
11 String parameterMap = context.getStringAttribute("parameterMap");
12 String parameterType = context.getStringAttribute("parameterType");
13 Class parameterTypeClass = resolveClass(parameterType);
14 String resultMap = context.getStringAttribute("resultMap");
15 String resultType = context.getStringAttribute("resultType");
//获取语言驱动， 我们自定义的语言驱动也是从这里读取的， 同时参数处理器也是从驱动定义的，自定义参数处理器也可以在自定义语言驱动里面去实现
16 String lang = context.getStringAttribute("lang");
17 LanguageDriver langDriver = getLanguageDriver(lang);
18
19 Class resultTypeClass = resolveClass(resultType);
20 String resultSetType = context.getStringAttribute("resultSetType");
21 StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
22 ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
23
24 String nodeName = context.getNode().getNodeName();
25 SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
26 boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
27 boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
28 boolean useCache = context.getBooleanAttribute("useCache", isSelect);
29 boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);
30
31 // Include Fragments before parsing
32 XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
33 includeParser.applyIncludes(context.getNode());
34
35 // Parse selectKey after includes and remove them.
36 processSelectKeyNodes(id, parameterTypeClass, langDriver);
37 //根据前面的语言驱动去获取对应的SqlSource。SqlSource有两种，一种是处理${}一种是处理#{}
38 // Parse the SQL (pre: and were parsed and removed)
39 SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
40 String resultSets = context.getStringAttribute("resultSets");
41 String keyProperty = context.getStringAttribute("keyProperty");
42 String keyColumn = context.getStringAttribute("keyColumn");
43 KeyGenerator keyGenerator;
44 String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
45 keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
46 if (configuration.hasKeyGenerator(keyStatementId)) {
47 keyGenerator = configuration.getKeyGenerator(keyStatementId);
48 } else {
49 keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
50 configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
51 ? new Jdbc3KeyGenerator() : new NoKeyGenerator();
52 }
53 获取节点所有属性内容，调用builderAssistant，实现是MapperBuilderAssistant 在XmlMapperBuilder构造器初始化时候就制定了
54 builderAssistant.addMappedS
