Mybatis框架解析之Builder解析
首先我们从builder这个类入手,首先我们注意到BaseBuilder,其实它的本质上市一个抽象类,它从本质上抽象出了Builder的一切,我猜想这里一定使用了建造者模式,但是这个抽象类里面居然没有抽象方法!
其中XXXValueOf方法,其实是把String字符串转换成了相对应的类型,如下代码。
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protected Boolean booleanValueOf(String value, Boolean defaultValue) { return value == null ? defaultValue : Boolean.valueOf(value); } protected Integer integerValueOf(String value, Integer defaultValue) { return value == null ? defaultValue : Integer.valueOf(value); } protected Set<String> stringSetValueOf(String value, String defaultValue) { value = (value == null ? defaultValue : value); return new HashSet<String>(Arrays.asList(value.split(","))); }
其中resoveXXXType的目的就是把string转换成相对应的类型。
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protected JdbcType resolveJdbcType(String alias) { if (alias == null) { return null; } try { return JdbcType.valueOf(alias); } catch (IllegalArgumentException e) { throw new BuilderException("Error resolving JdbcType. Cause: " + e, e); } } protected ResultSetType resolveResultSetType(String alias) { if (alias == null) { return null; } try { return ResultSetType.valueOf(alias); } catch (IllegalArgumentException e) { throw new BuilderException("Error resolving ResultSetType. Cause: " + e, e); } } protected ParameterMode resolveParameterMode(String alias) { if (alias == null) { return null; } try { return ParameterMode.valueOf(alias); } catch (IllegalArgumentException e) { throw new BuilderException("Error resolving ParameterMode. Cause: " + e, e); } }
下面的方法是通过字符串别名解析出相对应的类型,再从类型创建实例。
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protected Object createInstance(String alias) { Class<?> clazz = resolveClass(alias); if (clazz == null) { return null; } try { return resolveClass(alias).newInstance(); } catch (Exception e) { throw new BuilderException("Error creating instance. Cause: " + e, e); } } protected Class<?> resolveClass(String alias) { if (alias == null) { return null; } try { return resolveAlias(alias); } catch (Exception e) { throw new BuilderException("Error resolving class. Cause: " + e, e); } }
注意下面的,是2个不同的重载类,是第一个调用第二个。首先得到相对应的TypeHanlder类型,如果该TypeHanlder在typeHanlderRegisty注册中心有留存,那么返回,否则从javatype里创建一个新的。
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protected TypeHandler<?> resolveTypeHandler(Class<?> javaType, String typeHandlerAlias) { if (typeHandlerAlias == null) { return null; } Class<?> type = resolveClass(typeHandlerAlias); if (type != null && !TypeHandler.class.isAssignableFrom(type)) { throw new BuilderException("Type " + type.getName() + " is not a valid TypeHandler because it does not implement TypeHandler interface"); } @SuppressWarnings( "unchecked" ) // already verified it is a TypeHandler Class<? extends TypeHandler<?>> typeHandlerType = (Class<? extends TypeHandler<?>>) type; return resolveTypeHandler(javaType, typeHandlerType); } protected TypeHandler<?> resolveTypeHandler(Class<?> javaType, Class<? extends TypeHandler<?>> typeHandlerType) { if (typeHandlerType == null) { return null; } // javaType ignored for injected handlers see issue #746 for full detail TypeHandler<?> handler = typeHandlerRegistry.getMappingTypeHandler(typeHandlerType); if (handler == null) { // not in registry, create a new one handler = typeHandlerRegistry.getInstance(javaType, typeHandlerType); } return handler; }
其中MapperBuilderAssistant在此包下面,并且继承了BaseBuilder,下面对此类做一个解析,比如下面的就是解析命名空间的,就是包名。
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public String applyCurrentNamespace(String base, boolean isReference) { if (base == null) { return null; } if (isReference) { // is it qualified with any namespace yet? if (base.contains(".")) { return base; } } else { // is it qualified with this namespace yet? if (base.startsWith(currentNamespace + ".")) { return base; } if (base.contains(".")) { throw new BuilderException("Dots are not allowed in element names, please remove it from " + base); } } return currentNamespace + "." + base; }
下面的代码主要是用namespace得到cache的一个实例,就这么理解。
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public Cache useCacheRef(String namespace) { if (namespace == null) { throw new BuilderException("cache-ref element requires a namespace attribute."); } try { unresolvedCacheRef = true; Cache cache = configuration.getCache(namespace); if (cache == null) { throw new IncompleteElementException("No cache for namespace '" + namespace + "' could be found."); } currentCache = cache; unresolvedCacheRef = false; return cache; } catch (IllegalArgumentException e) { throw new IncompleteElementException("No cache for namespace '" + namespace + "' could be found.", e); } }
下面的方法是创建cache。
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public Cache useNewCache(Class<? extends Cache> typeClass, Class<? extends Cache> evictionClass, Long flushInterval, Integer size, boolean readWrite, boolean blocking, Properties props) { Cache cache = new CacheBuilder(currentNamespace) .implementation(valueOrDefault(typeClass, PerpetualCache.class)) .addDecorator(valueOrDefault(evictionClass, LruCache.class)) .clearInterval(flushInterval) .size(size) .readWrite(readWrite) .blocking(blocking) .properties(props) .build(); configuration.addCache(cache); currentCache = cache; return cache; }
其中有一个地方要弄清楚,就是Class<? extends Cache> typeClass, Class<? extends Cache> evictionClass的区别在哪里?在哪里呢?请看下图,一个是实现,一个是装饰者,你可以暂时理解为作用不同,就这么简单。
下面是addParameterMap方法的一些介绍。
public ParameterMap addParameterMap(String id, Class<?> parameterClass, List<ParameterMapping> parameterMappings) { //得到包名。 id = applyCurrentNamespace(id, false); //工厂方法创建参数Map,并添加到configuration中去。 ParameterMap parameterMap = new ParameterMap.Builder(configuration, id, parameterClass, parameterMappings).build(); configuration.addParameterMap(parameterMap); return parameterMap; }
下面是buildParameterMap的介绍,其实它也是利用了工厂方法骑构造。
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public ParameterMapping buildParameterMapping( Class<?> parameterType, String property, Class<?> javaType, JdbcType jdbcType, String resultMap, ParameterMode parameterMode, Class<? extends TypeHandler<?>> typeHandler, Integer numericScale) { resultMap = applyCurrentNamespace(resultMap, true); // Class parameterType = parameterMapBuilder.type(); Class<?> javaTypeClass = resolveParameterJavaType(parameterType, property, javaType, jdbcType); TypeHandler<?> typeHandlerInstance = resolveTypeHandler(javaTypeClass, typeHandler); return new ParameterMapping.Builder(configuration, property, javaTypeClass) .jdbcType(jdbcType) .resultMapId(resultMap) .mode(parameterMode) .numericScale(numericScale) .typeHandler(typeHandlerInstance) .build(); }
下面的是建立一个结果集,然后把结果集添加到configuration里面。
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public ResultMap addResultMap( String id, Class<?> type, String extend, Discriminator discriminator, List<ResultMapping> resultMappings, Boolean autoMapping) { id = applyCurrentNamespace(id, false); extend = applyCurrentNamespace(extend, true); if (extend != null) { if (!configuration.hasResultMap(extend)) { throw new IncompleteElementException("Could not find a parent resultmap with id '" + extend + "'"); } ResultMap resultMap = configuration.getResultMap(extend); List<ResultMapping> extendedResultMappings = new ArrayList<ResultMapping>(resultMap.getResultMappings()); extendedResultMappings.removeAll(resultMappings); // Remove parent constructor if this resultMap declares a constructor. boolean declaresConstructor = false; for (ResultMapping resultMapping : resultMappings) { if (resultMapping.getFlags().contains(ResultFlag.CONSTRUCTOR)) { declaresConstructor = true; break; } } if (declaresConstructor) { Iterator<ResultMapping> extendedResultMappingsIter = extendedResultMappings.iterator(); while (extendedResultMappingsIter.hasNext()) { if (extendedResultMappingsIter.next().getFlags().contains(ResultFlag.CONSTRUCTOR)) { extendedResultMappingsIter.remove(); } } } resultMappings.addAll(extendedResultMappings); } ResultMap resultMap = new ResultMap.Builder(configuration, id, type, resultMappings, autoMapping) .discriminator(discriminator) .build(); configuration.addResultMap(resultMap); return resultMap; }
当然,下面的也太多了,就不一一介绍了,还有一些这些结果集的一些Getter方法;有兴趣的可以自己去看看,不过我们从这里得到了一个很重要的东西,那就是贯穿上下文的一个东西:Configuration!,这个东西可以说是无处不在,不管是在基类,还是在派生类中。
我们还看到了一些工厂的Relover,那这些resover类其实也是调用了上面的一些public方法而已,没啥特别的,真的。
下面我们再看看SqlSourceBuilder 这个类,这个先从string解析成map,然后再判断是否是sql类型,如果是,继续解析。
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private ParameterMapping buildParameterMapping(String content) { Map<String, String> propertiesMap = parseParameterMapping(content); String property = propertiesMap.get("property"); Class<?> propertyType; if (metaParameters.hasGetter(property)) { // issue #448 get type from additional params propertyType = metaParameters.getGetterType(property); } else if (typeHandlerRegistry.hasTypeHandler(parameterType)) { propertyType = parameterType; } else if (JdbcType.CURSOR.name().equals(propertiesMap.get("jdbcType"))) { propertyType = java.sql.ResultSet.class; } else if (property == null || Map.class.isAssignableFrom(parameterType)) { propertyType = Object.class; } else { MetaClass metaClass = MetaClass.forClass(parameterType, configuration.getReflectorFactory()); if (metaClass.hasGetter(property)) { propertyType = metaClass.getGetterType(property); } else { propertyType = Object.class; } } ParameterMapping.Builder builder = new ParameterMapping.Builder(configuration, property, propertyType); Class<?> javaType = propertyType; String typeHandlerAlias = null; for (Map.Entry<String, String> entry : propertiesMap.entrySet()) { String name = entry.getKey(); String value = entry.getValue(); if ("javaType".equals(name)) { javaType = resolveClass(value); builder.javaType(javaType); } else if ("jdbcType".equals(name)) { builder.jdbcType(resolveJdbcType(value)); } else if ("mode".equals(name)) { builder.mode(resolveParameterMode(value)); } else if ("numericScale".equals(name)) { builder.numericScale(Integer.valueOf(value)); } else if ("resultMap".equals(name)) { builder.resultMapId(value); } else if ("typeHandler".equals(name)) { typeHandlerAlias = value; } else if ("jdbcTypeName".equals(name)) { builder.jdbcTypeName(value); } else if ("property".equals(name)) { // Do Nothing } else if ("expression".equals(name)) { throw new BuilderException("Expression based parameters are not supported yet"); } else { throw new BuilderException("An invalid property '" + name + "' was found in mapping #{" + content + "}. Valid properties are " + parameterProperties); } } if (typeHandlerAlias != null) { builder.typeHandler(resolveTypeHandler(javaType, typeHandlerAlias)); } return builder.build(); }
其中比较重要的就是下面的代码,下面做一个分析,首先会得到typeHanldler,然后再在buidler里对这个进行注册。
if (typeHandlerAlias != null) { builder.typeHandler(resolveTypeHandler(javaType, typeHandlerAlias)); } return builder.build();
我们关键是看看builder.build方法,它是一个private的方法,它的作用就是get到我们开始设置的值,下面的validate方法也是做一些基础验证的,具体的可以略过,没啥价值。
private void resolveTypeHandler() { if (parameterMapping.typeHandler == null && parameterMapping.javaType != null) { Configuration configuration = parameterMapping.configuration; TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry(); parameterMapping.typeHandler = typeHandlerRegistry.getTypeHandler(parameterMapping.javaType, parameterMapping.jdbcType); } }
下面我们再来看看这个类:StaticSqlSource 其实我觉得这个玩意没啥用!真的不是贬低写mybatis的人,真没看出有什么用,具体看下面的代码。
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public class StaticSqlSource implements SqlSource { private final String sql; private final List<ParameterMapping> parameterMappings; private final Configuration configuration; public StaticSqlSource(Configuration configuration, String sql) { this(configuration, sql, null); } public StaticSqlSource(Configuration configuration, String sql, List<ParameterMapping> parameterMappings) { this.sql = sql; this.parameterMappings = parameterMappings; this.configuration = configuration; } @Override public BoundSql getBoundSql(Object parameterObject) { return new BoundSql(configuration, sql, parameterMappings, parameterObject); }
这些类同级的包里面,还有一个XML的包,里面包含的DTD文件,以及一些工具类,大家理解这些东西,其实就是为了把烦人的XML转换成一个可用的configuration对象的的工具类就行了,真的没必要深究。
关于builder的annotation 大家应该不陌生了吧?我介绍了这么多。构造函数说得很清楚了,其实把一些基本的注解加进了,CRUD而已。
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public MapperAnnotationBuilder(Configuration configuration, Class<?> type) { String resource = type.getName().replace('.', '/') + ".java (best guess)"; this.assistant = new MapperBuilderAssistant(configuration, resource); this.configuration = configuration; this.type = type; sqlAnnotationTypes.add(Select.class); sqlAnnotationTypes.add(Insert.class); sqlAnnotationTypes.add(Update.class); sqlAnnotationTypes.add(Delete.class); sqlProviderAnnotationTypes.add(SelectProvider.class); sqlProviderAnnotationTypes.add(InsertProvider.class); sqlProviderAnnotationTypes.add(UpdateProvider.class); sqlProviderAnnotationTypes.add(DeleteProvider.class); }
有一个核心方法,比较重要:parse,作用很明显,就是转换呗,然后是从configuration拿玩意,然后转换成有用的东西。其实这个不就是我们写的mapper类的XML文件吗?!用过mybatis的人都知道的。注释写了一点,不过更深入了,我觉得没必要写了,靠大家自己去发掘。
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public void parse() { String resource = type.toString(); if (!configuration.isResourceLoaded(resource)) { //载入XML资源文件。 loadXmlResource(); //把资源文件添加到configuation里面。 configuration.addLoadedResource(resource); assistant.setCurrentNamespace(type.getName()); //修改assistant变量 parseCache(); //修改assistant变量2 parseCacheRef(); Method[] methods = type.getMethods(); for (Method method : methods) { try { // issue #237 if (!method.isBridge()) { parseStatement(method); } } catch (IncompleteElementException e) { configuration.addIncompleteMethod(new MethodResolver(this, method)); } } } parsePendingMethods(); }
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