Mybatis框架解析之Builder解析

時間 2019-11-06

原文原文鏈接

首先咱們從builder這個類入手，首先咱們注意到BaseBuilder,其實它的本質上市一個抽象類，它從本質上抽象出了Builder的一切，我猜測這裏必定使用了建造者模式，可是這個抽象類裏面竟然沒有抽象方法！java

其中XXXValueOf方法，實際上是把String字符串轉換成了相對應的類型，以下代碼。sql

  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(",")));
  }

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其中resoveXXXType的目的就是把string轉換成相對應的類型。express

  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);
    }
  }

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下面的方法是經過字符串別名解析出相對應的類型，再從類型建立實例。mybatis

 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);
    }
  }

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注意下面的，是2個不一樣的重載類，是第一個調用第二個。首先獲得相對應的TypeHanlder類型，若是該TypeHanlder在typeHanlderRegisty註冊中心有留存，那麼返回，不然從javatype裏建立一個新的。app

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;
  }

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其中MapperBuilderAssistant在此包下面，而且繼承了BaseBuilder,下面對此類作一個解析，好比下面的就是解析命名空間的，就是包名。ide

  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;
  }

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下面的代碼主要是用namespace獲得cache的一個實例，就這麼理解。函數

 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);
    }
  }

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下面的方法是建立cache。工具

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;
  }

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其中有一個地方要弄清楚，就是Class<? extends Cache> typeClass, Class<? extends Cache> evictionClass的區別在哪裏？在哪裏呢？請看下圖，一個是實現，一個是裝飾者，你能夠暫時理解爲做用不一樣，就這麼簡單。ui

下面是addParameterMap方法的一些介紹。this

  public ParameterMap addParameterMap(String id, Class<?> parameterClass, List<ParameterMapping> parameterMappings) {
    
    //獲得包名。
    id = applyCurrentNamespace(id, false);
    //工廠方法建立參數Map,並添加到configuration中去。
    ParameterMap parameterMap = new ParameterMap.Builder(configuration, id, parameterClass, parameterMappings).build();
    configuration.addParameterMap(parameterMap);
    return parameterMap;
  }

下面是buildParameterMap的介紹，其實它也是利用了工廠方法騎構造。

  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();
  }

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下面的是創建一個結果集，而後把結果集添加到configuration裏面。

  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;
  }

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固然，下面的也太多了，就不一一介紹了，還有一些這些結果集的一些Getter方法；有興趣的能夠本身去看看，不過咱們從這裏獲得了一個很重要的東西，那就是貫穿上下文的一個東西：Configuration!,這個東西能夠說是無處不在，無論是在基類，仍是在派生類中。

咱們還看到了一些工廠的Relover，那這些resover類其實也是調用了上面的一些public方法而已，沒啥特別的，真的。

下面咱們再看看SqlSourceBuilder 這個類，這個先從string解析成map,而後再判斷是不是sql類型，若是是，繼續解析。

    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();
    }

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其中比較重要的就是下面的代碼，下面作一個分析，首先會獲得typeHanldler,而後再在buidler裏對這個進行註冊。

     if (typeHandlerAlias != null) {
        builder.typeHandler(resolveTypeHandler(javaType, typeHandlerAlias));
      }
      return builder.build();

咱們關鍵是看看builder.build方法，它是一個private的方法，它的做用就是get到咱們開始設置的值，下面的validate方法也是作一些基礎驗證的，具體的能夠略過，沒啥價值。

    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);
      }
    }

下面咱們再來看看這個類:StaticSqlSource 其實我以爲這個玩意沒啥用！真的不是貶低寫mybatis的人，真沒看出有什麼用，具體看下面的代碼。

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);
  }

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這些類同級的包裏面，還有一個XML的包，裏面包含的DTD文件，以及一些工具類，你們理解這些東西，其實就是爲了把煩人的XML轉換成一個可用的configuration對象的的工具類就好了，真的不必深究。

關於builder的annotation 你們應該不陌生了吧？我介紹了這麼多。構造函數說得很清楚了，其實把一些基本的註解加進了，CRUD而已。

  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);
  }

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有一個核心方法，比較重要:parse,做用很明顯，就是轉換唄，而後是從configuration拿玩意，而後轉換成有用的東西。其實這個不就是咱們寫的mapper類的XML文件嗎？！用過mybatis的人都知道的。註釋寫了一點，不過更深刻了，我以爲不必寫了，靠你們本身去發掘。

  public void parse() {
    String resource = type.toString();
    if (!configuration.isResourceLoaded(resource)) {
      //載入XML資源文件。
      loadXmlResource();
      
      //把資源文件添加到configuation裏面。
      configuration.addLoadedResource(resource);
      assistant.setCurrentNamespace(type.getName());
      //修改assistant變量
      parseCache();
      //修改assistant變量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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