深入浅出Mybatis系列（七）---TypeHandler简介

　　无论是 MyBatis 在预处理语句（PreparedStatement）中设置一个参数时，还是从结果集中取出一个值时，都会用类型处理器将获取的值以合适的方式转换成 Java 类型。Mybatis默认为我们实现了许多TypeHandler, 当我们没有配置指定TypeHandler时，Mybatis会根据参数或者返回结果的不同，默认为我们选择合适的TypeHandler处理。

那么，Mybatis为我们实现了哪些TypeHandler呢? 我们怎么自定义实现一个TypeHandler ? 这些都会在接下来的mybatis的源码中看到。

在看源码之前，还是像之前一样，先看看怎么配置吧？

<configuration>

    <typeHandlers>

      <!--

          当配置package的时候，mybatis会去配置的package扫描TypeHandler

          <package name="com.dy.demo"/>

       -->

      <!-- handler属性直接配置我们要指定的TypeHandler -->

      <typeHandler handler=""/>

      <!-- javaType 配置java类型，例如String, 如果配上javaType, 那么指定的typeHandler就只作用于指定的类型 -->

      <typeHandler javaType="" handler=""/>

      <!-- jdbcType 配置数据库基本数据类型，例如varchar, 如果配上jdbcType, 那么指定的typeHandler就只作用于指定的类型  -->

      <typeHandler jdbcType="" handler=""/>

      <!-- 也可两者都配置 -->

      <typeHandler javaType="" jdbcType="" handler=""/>

  </typeHandlers>

  ......

</configuration>

上面简单介绍了一下TypeHandler, 下面就看看mybatis中TypeHandler的源码了。

=========================================================我是源码分割线==========================================================

老规矩，先从对xml的解析讲起：

/**

 * 解析typeHandlers节点

 */

private void typeHandlerElement(XNode parent) throws Exception {

    if (parent != null) {

      for (XNode child : parent.getChildren()) {

        //子节点为package时，获取其name属性的值，然后自动扫描package下的自定义typeHandler

        if ("package".equals(child.getName())) {

          String typeHandlerPackage = child.getStringAttribute("name");

          typeHandlerRegistry.register(typeHandlerPackage);

        } else {

          //子节点为typeHandler时， 可以指定javaType属性， 也可以指定jdbcType, 也可两者都指定

          //javaType 是指定java类型

          //jdbcType 是指定jdbc类型（数据库类型： 如varchar）

          String javaTypeName = child.getStringAttribute("javaType");

          String jdbcTypeName = child.getStringAttribute("jdbcType");

          //handler就是我们配置的typeHandler

          String handlerTypeName = child.getStringAttribute("handler");

          //resolveClass方法就是我们上篇文章所讲的TypeAliasRegistry里面处理别名的方法

          Class<?> javaTypeClass = resolveClass(javaTypeName);

          //JdbcType是一个枚举类型，resolveJdbcType方法是在获取枚举类型的值

          JdbcType jdbcType = resolveJdbcType(jdbcTypeName);

          Class<?> typeHandlerClass = resolveClass(handlerTypeName);

          //注册typeHandler, typeHandler通过TypeHandlerRegistry这个类管理

          if (javaTypeClass != null) {

            if (jdbcType == null) {

              typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);

            } else {

              typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);

            }

          } else {

            typeHandlerRegistry.register(typeHandlerClass);

          }

        }

      }

    }

}

接下来看看TypeHandler的管理注册类：

TypeHandlerRegistry：

/**

 * typeHandler注册管理类

 */

public final class TypeHandlerRegistry {

  //源码一上来，二话不说，几个大大的HashMap就出现，这不又跟上次讲的typeAliases的注册类似么

  //基本数据类型与其包装类

  private static final Map<Class<?>, Class<?>> reversePrimitiveMap = new HashMap<Class<?>, Class<?>>() {

    private static final long serialVersionUID = 1L;

    {

      put(Byte.class, byte.class);

      put(Short.class, short.class);

      put(Integer.class, int.class);

      put(Long.class, long.class);

      put(Float.class, float.class);

      put(Double.class, double.class);

      put(Boolean.class, boolean.class);

      put(Character.class, char.class);

    }

  };

  //这几个MAP不用说就知道存的是什么东西吧，命名的好处

  private final Map<JdbcType, TypeHandler<?>> JDBC_TYPE_HANDLER_MAP = new EnumMap<JdbcType, TypeHandler<?>>(JdbcType.class);

  private final Map<Type, Map<JdbcType, TypeHandler<?>>> TYPE_HANDLER_MAP = new HashMap<Type, Map<JdbcType, TypeHandler<?>>>();

  private final TypeHandler<Object> UNKNOWN_TYPE_HANDLER = new UnknownTypeHandler(this);

  private final Map<Class<?>, TypeHandler<?>> ALL_TYPE_HANDLERS_MAP = new HashMap<Class<?>, TypeHandler<?>>();

  //就像上篇文章讲的typeAliases一样，mybatis也默认给我们注册了不少的typeHandler

  //具体如下

  public TypeHandlerRegistry() {

    register(Boolean.class, new BooleanTypeHandler());

    register(boolean.class, new BooleanTypeHandler());

    register(JdbcType.BOOLEAN, new BooleanTypeHandler());

    register(JdbcType.BIT, new BooleanTypeHandler());

    register(Byte.class, new ByteTypeHandler());

    register(byte.class, new ByteTypeHandler());

    register(JdbcType.TINYINT, new ByteTypeHandler());

    register(Short.class, new ShortTypeHandler());

    register(short.class, new ShortTypeHandler());

    register(JdbcType.SMALLINT, new ShortTypeHandler());

    register(Integer.class, new IntegerTypeHandler());

    register(int.class, new IntegerTypeHandler());

    register(JdbcType.INTEGER, new IntegerTypeHandler());

    register(Long.class, new LongTypeHandler());

    register(long.class, new LongTypeHandler());

    register(Float.class, new FloatTypeHandler());

    register(float.class, new FloatTypeHandler());

    register(JdbcType.FLOAT, new FloatTypeHandler());

    register(Double.class, new DoubleTypeHandler());

    register(double.class, new DoubleTypeHandler());

    register(JdbcType.DOUBLE, new DoubleTypeHandler());

    register(String.class, new StringTypeHandler());

    register(String.class, JdbcType.CHAR, new StringTypeHandler());

    register(String.class, JdbcType.CLOB, new ClobTypeHandler());

    register(String.class, JdbcType.VARCHAR, new StringTypeHandler());

    register(String.class, JdbcType.LONGVARCHAR, new ClobTypeHandler());

    register(String.class, JdbcType.NVARCHAR, new NStringTypeHandler());

    register(String.class, JdbcType.NCHAR, new NStringTypeHandler());

    register(String.class, JdbcType.NCLOB, new NClobTypeHandler());

    register(JdbcType.CHAR, new StringTypeHandler());

    register(JdbcType.VARCHAR, new StringTypeHandler());

    register(JdbcType.CLOB, new ClobTypeHandler());

    register(JdbcType.LONGVARCHAR, new ClobTypeHandler());

    register(JdbcType.NVARCHAR, new NStringTypeHandler());

    register(JdbcType.NCHAR, new NStringTypeHandler());

    register(JdbcType.NCLOB, new NClobTypeHandler());

    register(Object.class, JdbcType.ARRAY, new ArrayTypeHandler());

    register(JdbcType.ARRAY, new ArrayTypeHandler());

    register(BigInteger.class, new BigIntegerTypeHandler());

    register(JdbcType.BIGINT, new LongTypeHandler());

    register(BigDecimal.class, new BigDecimalTypeHandler());

    register(JdbcType.REAL, new BigDecimalTypeHandler());

    register(JdbcType.DECIMAL, new BigDecimalTypeHandler());

    register(JdbcType.NUMERIC, new BigDecimalTypeHandler());

    register(Byte[].class, new ByteObjectArrayTypeHandler());

    register(Byte[].class, JdbcType.BLOB, new BlobByteObjectArrayTypeHandler());

    register(Byte[].class, JdbcType.LONGVARBINARY, new BlobByteObjectArrayTypeHandler());

    register(byte[].class, new ByteArrayTypeHandler());

    register(byte[].class, JdbcType.BLOB, new BlobTypeHandler());

    register(byte[].class, JdbcType.LONGVARBINARY, new BlobTypeHandler());

    register(JdbcType.LONGVARBINARY, new BlobTypeHandler());

    register(JdbcType.BLOB, new BlobTypeHandler());

    register(Object.class, UNKNOWN_TYPE_HANDLER);

    register(Object.class, JdbcType.OTHER, UNKNOWN_TYPE_HANDLER);

    register(JdbcType.OTHER, UNKNOWN_TYPE_HANDLER);

    register(Date.class, new DateTypeHandler());

    register(Date.class, JdbcType.DATE, new DateOnlyTypeHandler());

    register(Date.class, JdbcType.TIME, new TimeOnlyTypeHandler());

    register(JdbcType.TIMESTAMP, new DateTypeHandler());

    register(JdbcType.DATE, new DateOnlyTypeHandler());

    register(JdbcType.TIME, new TimeOnlyTypeHandler());

    register(java.sql.Date.class, new SqlDateTypeHandler());

    register(java.sql.Time.class, new SqlTimeTypeHandler());

    register(java.sql.Timestamp.class, new SqlTimestampTypeHandler());

    // issue #273

    register(Character.class, new CharacterTypeHandler());

    register(char.class, new CharacterTypeHandler());

  }

  public boolean hasTypeHandler(Class<?> javaType) {

    return hasTypeHandler(javaType, null);

  }

  public boolean hasTypeHandler(TypeReference<?> javaTypeReference) {

    return hasTypeHandler(javaTypeReference, null);

  }

  public boolean hasTypeHandler(Class<?> javaType, JdbcType jdbcType) {

    return javaType != null && getTypeHandler((Type) javaType, jdbcType) != null;

  }

  public boolean hasTypeHandler(TypeReference<?> javaTypeReference, JdbcType jdbcType) {

    return javaTypeReference != null && getTypeHandler(javaTypeReference, jdbcType) != null;

  }

  public TypeHandler<?> getMappingTypeHandler(Class<? extends TypeHandler<?>> handlerType) {

    return ALL_TYPE_HANDLERS_MAP.get(handlerType);

  }

  public <T> TypeHandler<T> getTypeHandler(Class<T> type) {

    return getTypeHandler((Type) type, null);

  }

  public <T> TypeHandler<T> getTypeHandler(TypeReference<T> javaTypeReference) {

    return getTypeHandler(javaTypeReference, null);

  }

  public TypeHandler<?> getTypeHandler(JdbcType jdbcType) {

    return JDBC_TYPE_HANDLER_MAP.get(jdbcType);

  }

  public <T> TypeHandler<T> getTypeHandler(Class<T> type, JdbcType jdbcType) {

    return getTypeHandler((Type) type, jdbcType);

  }

  public <T> TypeHandler<T> getTypeHandler(TypeReference<T> javaTypeReference, JdbcType jdbcType) {

    return getTypeHandler(javaTypeReference.getRawType(), jdbcType);

  }

  private <T> TypeHandler<T> getTypeHandler(Type type, JdbcType jdbcType) {

    Map<JdbcType, TypeHandler<?>> jdbcHandlerMap = TYPE_HANDLER_MAP.get(type);

    TypeHandler<?> handler = null;

    if (jdbcHandlerMap != null) {

      handler = jdbcHandlerMap.get(jdbcType);

      if (handler == null) {

        handler = jdbcHandlerMap.get(null);

      }

    }

    if (handler == null && type != null && type instanceof Class && Enum.class.isAssignableFrom((Class<?>) type)) {

      handler = new EnumTypeHandler((Class<?>) type);

    }

    @SuppressWarnings("unchecked")

    // type drives generics here

    TypeHandler<T> returned = (TypeHandler<T>) handler;

    return returned;

  }

  public TypeHandler<Object> getUnknownTypeHandler() {

    return UNKNOWN_TYPE_HANDLER;

  }

  public void register(JdbcType jdbcType, TypeHandler<?> handler) {

    JDBC_TYPE_HANDLER_MAP.put(jdbcType, handler);

  }

  //

  // REGISTER INSTANCE

  //

  /**

   * 只配置了typeHandler, 没有配置jdbcType 或者javaType

   */

  @SuppressWarnings("unchecked")

  public <T> void register(TypeHandler<T> typeHandler) {

    boolean mappedTypeFound = false;

    //在自定义typeHandler的时候，可以加上注解MappedTypes 去指定关联的javaType

    //因此，此处需要扫描MappedTypes注解

    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);

    }

  }

  /**

   * 配置了typeHandlerhe和javaType

   */

  public <T> void register(Class<T> javaType, TypeHandler<? extends T> typeHandler) {

    register((Type) javaType, typeHandler);

  }

  private <T> void register(Type javaType, TypeHandler<? extends T> typeHandler) {

    //扫描注解MappedJdbcTypes

    MappedJdbcTypes mappedJdbcTypes = typeHandler.getClass().getAnnotation(MappedJdbcTypes.class);

    if (mappedJdbcTypes != null) {

      for (JdbcType handledJdbcType : mappedJdbcTypes.value()) {

        register(javaType, handledJdbcType, typeHandler);

      }

      if (mappedJdbcTypes.includeNullJdbcType()) {

        register(javaType, null, typeHandler);

      }

    } else {

      register(javaType, null, typeHandler);

    }

  }

  public <T> void register(TypeReference<T> javaTypeReference, TypeHandler<? extends T> handler) {

    register(javaTypeReference.getRawType(), handler);

  }

  /**

   * typeHandlerhe、javaType、jdbcType都配置了

   */

  public <T> void register(Class<T> type, JdbcType jdbcType, TypeHandler<? extends T> handler) {

    register((Type) type, jdbcType, handler);

  }

  /**

   * 注册typeHandler的核心方法

   * 就是向Map新增数据而已

   */

  private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) {

    if (javaType != null) {

      Map<JdbcType, TypeHandler<?>> map = TYPE_HANDLER_MAP.get(javaType);

      if (map == null) {

        map = new HashMap<JdbcType, TypeHandler<?>>();

        TYPE_HANDLER_MAP.put(javaType, map);

      }

      map.put(jdbcType, handler);

      if (reversePrimitiveMap.containsKey(javaType)) {

        register(reversePrimitiveMap.get(javaType), jdbcType, handler);

      }

    }

    ALL_TYPE_HANDLERS_MAP.put(handler.getClass(), handler);

  }

  //

  // REGISTER CLASS

  //

  // Only handler type

  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));

    }

  }

  // java type + handler type

  public void register(Class<?> javaTypeClass, Class<?> typeHandlerClass) {

    register(javaTypeClass, getInstance(javaTypeClass, typeHandlerClass));

  }

  // java type + jdbc type + handler type

  public void register(Class<?> javaTypeClass, JdbcType jdbcType, Class<?> typeHandlerClass) {

    register(javaTypeClass, jdbcType, getInstance(javaTypeClass, typeHandlerClass));

  }

  // Construct a handler (used also from Builders)

  @SuppressWarnings("unchecked")

  public <T> TypeHandler<T> getInstance(Class<?> javaTypeClass, Class<?> typeHandlerClass) {

    if (javaTypeClass != null) {

      try {

        Constructor<?> c = typeHandlerClass.getConstructor(Class.class);

        return (TypeHandler<T>) c.newInstance(javaTypeClass);

      } catch (NoSuchMethodException ignored) {

        // ignored

      } catch (Exception e) {

        throw new TypeException("Failed invoking constructor for handler " + typeHandlerClass, e);

      }

    }

    try {

      Constructor<?> c = typeHandlerClass.getConstructor();

      return (TypeHandler<T>) c.newInstance();

    } catch (Exception e) {

      throw new TypeException("Unable to find a usable constructor for " + typeHandlerClass, e);

    }

  }

  /**

   * 根据指定的pacakge去扫描自定义的typeHander，然后注册

   */

  public void register(String packageName) {

    ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();

    resolverUtil.find(new ResolverUtil.IsA(TypeHandler.class), packageName);

    Set<Class<? extends Class<?>>> handlerSet = resolverUtil.getClasses();

    for (Class<?> type : handlerSet) {

      //Ignore inner classes and interfaces (including package-info.java) and abstract classes

      if (!type.isAnonymousClass() && !type.isInterface() && !Modifier.isAbstract(type.getModifiers())) {

        register(type);

      }

    }

  }

  // get information

  /**

   * 通过configuration对象可以获取已注册的所有typeHandler

   */

  public Collection<TypeHandler<?>> getTypeHandlers() {

    return Collections.unmodifiableCollection(ALL_TYPE_HANDLERS_MAP.values());

  }

}

提示从 3.4.5 开始，MyBatis 默认支持 JSR-310（日期和时间 API）。

=====================================================自定义TypeHandler分割线============================================================

ExampleTypeHandler:

@MappedJdbcTypes(JdbcType.VARCHAR)

//此处如果不用注解指定jdbcType, 那么，就可以在配置文件中通过"jdbcType"属性指定， 同理， javaType 也可通过 @MappedTypes指定

public class ExampleTypeHandler extends BaseTypeHandler<String> {

  @Override

  public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException {

    ps.setString(i, parameter);

  }

  @Override

  public String getNullableResult(ResultSet rs, String columnName) throws SQLException {

    return rs.getString(columnName);

  }

  @Override

  public String getNullableResult(ResultSet rs, int columnIndex) throws SQLException {

    return rs.getString(columnIndex);

  }

  @Override

  public String getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {

    return cs.getString(columnIndex);

  }

}

然后，就该配置我们的自定义TypeHandler了：

<configuration>

  <typeHandlers>

      <!-- 由于自定义的TypeHandler在定义时已经通过注解指定了jdbcType, 所以此处不用再配置jdbcType -->

      <typeHandler handler="ExampleTypeHandler"/>

  </typeHandlers>

  ......

</configuration>

也就是说，我们在自定义TypeHandler的时候，可以在TypeHandler通过@MappedJdbcTypes指定jdbcType, 通过 @MappedTypes 指定javaType, 如果没有使用注解指定，那么我们就需要在配置文件中配置。

巴特西

深入浅出Mybatis系列（七）---TypeHandler简介

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