MyBatis TypeHandler的注册和使用流程分析

public final class TypeHandlerRegistry {

  //根据JdbcType对应的TypeHandler(优先级比较低)
  private final Map<JdbcType, TypeHandler<?>>  jdbcTypeHandlerMap = new EnumMap<>(JdbcType.class);
  //参数类型对应的TypeHandler(优先级比较高)
  private final Map<Type, Map<JdbcType, TypeHandler<?>>> typeHandlerMap = new ConcurrentHashMap<>();
  //一个通用的TypeHandler
  private final TypeHandler<Object> unknownTypeHandler = new UnknownTypeHandler(this);
  //保存所有的TypeHandler， Key是TypeHandler的Class，Value是TypeHandle对象
  private final Map<Class<?>, TypeHandler<?>> allTypeHandlersMap = new HashMap<>();

  private static final Map<JdbcType, TypeHandler<?>> NULL_TYPE_HANDLER_MAP = Collections.emptyMap();

  private Class<? extends TypeHandler> defaultEnumTypeHandler = EnumTypeHandler.class;
//...

  //自定义的TypeHandler一般都在这里注册（一般都是配置了type-handlers-package: com.tenmao.boot.mybatis.handler
  public void register(Class<?> typeHandlerClass) {
    boolean mappedTypeFound = false;
    MappedTypes mappedTypes = typeHandlerClass.getAnnotation(MappedTypes.class);
    if (mappedTypes != null) {
      for (Class<?> javaTypeClass : mappedTypes.value()) {
        register(javaTypeClass, typeHandlerClass);
        mappedTypeFound = true;
      }
    }
    if (!mappedTypeFound) {
      register(getInstance(null, typeHandlerClass));
    }
  }

  //...
  //这里注册了TypeHandler对象(自定义的TypeHandler一般在这里注册)
  @SuppressWarnings("unchecked")
  public <T> void register(TypeHandler<T> typeHandler) {
    boolean mappedTypeFound = false;
    MappedTypes mappedTypes = typeHandler.getClass().getAnnotation(MappedTypes.class);
    if (mappedTypes != null) {
      for (Class<?> handledType : mappedTypes.value()) {
        register(handledType, typeHandler);
        mappedTypeFound = true;
      }
    }
    // @since 3.1.0 - try to auto-discover the mapped type
    if (!mappedTypeFound && typeHandler instanceof TypeReference) {
      try {
        TypeReference<T> typeReference = (TypeReference<T>) typeHandler;
        register(typeReference.getRawType(), typeHandler);
        mappedTypeFound = true;
      } catch (Throwable t) {
        // maybe users define the TypeReference with a different type and are not assignable, so just ignore it
      }
    }
    if (!mappedTypeFound) {
      register((Class<T>) null, typeHandler);
    }
  }
}

mybatis.type-handlers-package=com.tenmao.boot.mybatis.handler

  protected SqlSessionFactory buildSqlSessionFactory() throws Exception {

    final Configuration targetConfiguration;

    XMLConfigBuilder xmlConfigBuilder = null;
    if (this.configuration != null) {
      targetConfiguration = this.configuration;
      if (targetConfiguration.getVariables() == null) {
        targetConfiguration.setVariables(this.configurationProperties);
      } else if (this.configurationProperties != null) {
        targetConfiguration.getVariables().putAll(this.configurationProperties);
      }
    } else if (this.configLocation != null) {
      xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
      targetConfiguration = xmlConfigBuilder.getConfiguration();
    } else {
      LOGGER.debug(
          () -> "Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
      targetConfiguration = new Configuration();
      Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
    }

    Optional.ofNullable(this.objectFactory).ifPresent(targetConfiguration::setObjectFactory);
    Optional.ofNullable(this.objectWrapperFactory).ifPresent(targetConfiguration::setObjectWrapperFactory);
    Optional.ofNullable(this.vfs).ifPresent(targetConfiguration::setVfsImpl);

    if (hasLength(this.typeAliasesPackage)) {
      scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream()
          .filter(clazz -> !clazz.isAnonymousClass()).filter(clazz -> !clazz.isInterface())
          .filter(clazz -> !clazz.isMemberClass()).forEach(targetConfiguration.getTypeAliasRegistry()::registerAlias);
    }

    if (!isEmpty(this.typeAliases)) {
      Stream.of(this.typeAliases).forEach(typeAlias -> {
        targetConfiguration.getTypeAliasRegistry().registerAlias(typeAlias);
        LOGGER.debug(() -> "Registered type alias: '" + typeAlias + "'");
      });
    }

    if (!isEmpty(this.plugins)) {
      Stream.of(this.plugins).forEach(plugin -> {
        targetConfiguration.addInterceptor(plugin);
        LOGGER.debug(() -> "Registered plugin: '" + plugin + "'");
      });
    }

    //扫描包中的TypeHandler
    if (hasLength(this.typeHandlersPackage)) {
      scanClasses(this.typeHandlersPackage, TypeHandler.class).stream().filter(clazz -> !clazz.isAnonymousClass())
          .filter(clazz -> !clazz.isInterface()).filter(clazz -> !Modifier.isAbstract(clazz.getModifiers()))
          .filter(clazz -> ClassUtils.getConstructorIfAvailable(clazz) != null)
          .forEach(targetConfiguration.getTypeHandlerRegistry()::register);
    }

    if (!isEmpty(this.typeHandlers)) {
      Stream.of(this.typeHandlers).forEach(typeHandler -> {
        targetConfiguration.getTypeHandlerRegistry().register(typeHandler);
        LOGGER.debug(() -> "Registered type handler: '" + typeHandler + "'");
      });
    }

    if (!isEmpty(this.scriptingLanguageDrivers)) {
      Stream.of(this.scriptingLanguageDrivers).forEach(languageDriver -> {
        targetConfiguration.getLanguageRegistry().register(languageDriver);
        LOGGER.debug(() -> "Registered scripting language driver: '" + languageDriver + "'");
      });
    }
    Optional.ofNullable(this.defaultScriptingLanguageDriver)
        .ifPresent(targetConfiguration::setDefaultScriptingLanguage);

    if (this.databaseIdProvider != null) {// fix #64 set databaseId before parse mapper xmls
      try {
        targetConfiguration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
      } catch (SQLException e) {
        throw new NestedIOException("Failed getting a databaseId", e);
      }
    }

    Optional.ofNullable(this.cache).ifPresent(targetConfiguration::addCache);

    if (xmlConfigBuilder != null) {
      try {
        xmlConfigBuilder.parse();
        LOGGER.debug(() -> "Parsed configuration file: '" + this.configLocation + "'");
      } catch (Exception ex) {
        throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
      } finally {
        ErrorContext.instance().reset();
      }
    }

    targetConfiguration.setEnvironment(new Environment(this.environment,
        this.transactionFactory == null ? new SpringManagedTransactionFactory() : this.transactionFactory,
        this.dataSource));

    if (this.mapperLocations != null) {
      if (this.mapperLocations.length == 0) {
        LOGGER.warn(() -> "Property 'mapperLocations' was specified but matching resources are not found.");
      } else {
        for (Resource mapperLocation : this.mapperLocations) {
          if (mapperLocation == null) {
            continue;
          }
          try {
            XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
                targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
            xmlMapperBuilder.parse();
          } catch (Exception e) {
            throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
          } finally {
            ErrorContext.instance().reset();
          }
          LOGGER.debug(() -> "Parsed mapper file: '" + mapperLocation + "'");
        }
      }
    } else {
      LOGGER.debug(() -> "Property 'mapperLocations' was not specified.");
    }

    return this.sqlSessionFactoryBuilder.build(targetConfiguration);
  }

  /**
   * Gets the type handler to use when reading the result set.
   * Tries to get from the TypeHandlerRegistry by searching for the property type.
   * If not found it gets the column JDBC type and tries to get a handler for it.
   *
   * @param propertyType
   * @param columnName
   * @return
   */
  public TypeHandler<?> getTypeHandler(Class<?> propertyType, String columnName) {
    TypeHandler<?> handler = null;
    Map<Class<?>, TypeHandler<?>> columnHandlers = typeHandlerMap.get(columnName);
    if (columnHandlers == null) {
      columnHandlers = new HashMap<>();
      typeHandlerMap.put(columnName, columnHandlers);
    } else {
      handler = columnHandlers.get(propertyType);
    }
    if (handler == null) {
      JdbcType jdbcType = getJdbcType(columnName);
      handler = typeHandlerRegistry.getTypeHandler(propertyType, jdbcType);
      // Replicate logic of UnknownTypeHandler#resolveTypeHandler
      // See issue #59 comment 10
      if (handler == null || handler instanceof UnknownTypeHandler) {
        final int index = columnNames.indexOf(columnName);
        final Class<?> javaType = resolveClass(classNames.get(index));
        if (javaType != null && jdbcType != null) {
          handler = typeHandlerRegistry.getTypeHandler(javaType, jdbcType);
        } else if (javaType != null) {
          handler = typeHandlerRegistry.getTypeHandler(javaType);
        } else if (jdbcType != null) {
          handler = typeHandlerRegistry.getTypeHandler(jdbcType);
        }
      }
      if (handler == null || handler instanceof UnknownTypeHandler) {
        handler = new ObjectTypeHandler();
      }
      columnHandlers.put(propertyType, handler);
    }
    return handler;
  }

org.apache.ibatis.scripting.xmltags.XMLLanguageDriver#createSqlSource(org.apache.ibatis.session.Configuration, java.lang.String, java.lang.Class<?>)
org.apache.ibatis.builder.SqlSourceBuilder#parse
org.apache.ibatis.builder.SqlSourceBuilder.ParameterMappingTokenHandler#handleToken
org.apache.ibatis.builder.SqlSourceBuilder.ParameterMappingTokenHandler#buildParameterMapping
org.apache.ibatis.mapping.ParameterMapping.Builder#build
org.apache.ibatis.mapping.ParameterMapping.Builder#resolveTypeHandler

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);
    }
}