[Java知识库] Mybatis类型处理器

开发: C++知识库 Java知识库 JavaScript Python PHP知识库人工智能区块链大数据移动开发嵌入式开发工具数据结构与算法开发测试游戏开发网络协议系统运维
教程: HTML教程 CSS教程 JavaScript教程 Go语言教程 JQuery教程 VUE教程 VUE3教程 Bootstrap教程 SQL数据库教程 C语言教程 C++教程 Java教程 Python教程 Python3教程 C#教程
数码: 电脑笔记本显卡显示器固态硬盘硬盘耳机手机 iphone vivo oppo 小米华为单反装机图拉丁

-> Java知识库 -> Mybatis类型处理器 -> 正文阅读

[Java知识库]Mybatis类型处理器

一、TypeHandler

Mybatis版本3.5.4

在项目开发中经常会遇到一个问题

当我们在javabean中自定义了枚举类型或者其它某个类型，但是在数据库中存储时往往需要转换成数据库对应的类型，并且在从数据库中取出来时也需要将数据库类型转换为javabean中的对应类型。比如：javabean中字段类型为Date，数据库中存储的是varchar类型；javabean中字段类型是Enum，数据库中存储的是String或者Integer。

因为有大量类似数据的转换，手动转换类型进行存储和查询已经过于麻烦。MyBatis为我们提供了解决办法：TypeHandler类型处理器。

public interface TypeHandler<T> {
  
   将参数从java数据类型转化成jdbc数据类型，然后绑定到sql上
  void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;
  
  //从数据库中读取的列数据转换成java数据类型
  T getResult(ResultSet rs, String columnName) throws SQLException;
  T getResult(ResultSet rs, int columnIndex) throws SQLException;
  T getResult(CallableStatement cs, int columnIndex) throws SQLException;
}

如果我想自定义我们自己的类型处理器，可以继续他的子类BaseTypeHandler，目前常用的类型处理器都继承于TypeHandler的子类BaseTypeHandler

public abstract class BaseTypeHandler<T> extends TypeReference<T> implements TypeHandler<T> {

  @Deprecated
  protected Configuration configuration;

  @Deprecated
  public void setConfiguration(Configuration c) {
    this.configuration = c;
  }


  public abstract void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;

  public abstract T getNullableResult(ResultSet rs, String columnName) throws SQLException;

  public abstract T getNullableResult(ResultSet rs, int columnIndex) throws SQLException;

  public abstract T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException;
  
  @Override
  public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
    if (parameter == null) {
      if (jdbcType == null) {
        throw new TypeException("");
      }
      try {
        //处理把null映射成数据库类型的情况
        ps.setNull(i, jdbcType.TYPE_CODE);
      } catch (SQLException e) {
        throw new TypeException(" ");
      }
    } else {
      try {
        //穿参不为空时，怎么把null映射成数据库类型
        setNonNullParameter(ps, i, parameter, jdbcType);
      } catch (Exception e) {
        throw new TypeException("" );
      }
    }
  }

  @Override
  public T getResult(ResultSet rs, String columnName) throws SQLException {
    try {
      return getNullableResult(rs, columnName);
    } catch (Exception e) {
      throw new ResultMapException(" " + e, e);
    }
  }

  @Override
  public T getResult(ResultSet rs, int columnIndex) throws SQLException {
    try {
      return getNullableResult(rs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException(" " + e, e);
    }
  }

  @Override
  public T getResult(CallableStatement cs, int columnIndex) throws SQLException {
    try {
      return getNullableResult(cs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException(" " + e, e);
    }
  }
}

二、类型处理器注册源码分析

在纯Mybatis环境中，Mybatis通从这段代码开始获取我们注册的类型处理器信息

private void typeHandlerElement(XNode parent) {
    if (parent != null) {
      for (XNode child : parent.getChildren()) {
        if ("package".equals(child.getName())) {
          String typeHandlerPackage = child.getStringAttribute("name");
          typeHandlerRegistry.register(typeHandlerPackage);
        } else {
          String javaTypeName = child.getStringAttribute("javaType");
          String jdbcTypeName = child.getStringAttribute("jdbcType");
          String handlerTypeName = child.getStringAttribute("handler");
          Class<?> javaTypeClass = resolveClass(javaTypeName);
          JdbcType jdbcType = resolveJdbcType(jdbcTypeName);
          Class<?> typeHandlerClass = resolveClass(handlerTypeName);
          if (javaTypeClass != null) {
            if (jdbcType == null) {
              typeHandlerRegistry.register(javaTypeClass, typeHandlerClass);
            } else {
              typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass);
            }
          } else {
            typeHandlerRegistry.register(typeHandlerClass);
          }
        }
      }
    }
  }

目前常见类型处理器注册方式有2种

2.1 package注册方式源码分析

public final class TypeHandlerRegistry {

	   // 记录JdbcType和TypeHandler之间的对应关系，其中JdbcType是一个枚举类型，它定义对应的JDBC类型
	  // 该集合主要用于从结果集读取数据时，将数据从Jdbc类型转换成Java类型
	  private final Map<JdbcType, TypeHandler<?>>  jdbcTypeHandlerMap = new EnumMap<>(JdbcType.class);
	  
	  // 记录了Java类型向指定的JdbcType转换时，需要使用的TypeHandler对象。例如：Java类型中的String可能
	  // 转换成数据库的char、varchar等多种类型，所以存在一对多的关系，所以值要用Map来存储
	  private final Map<Type, Map<JdbcType, TypeHandler<?>>> typeHandlerMap = new ConcurrentHashMap<>();
	  
	  // 未知类型对象的TypeHandler
	  private final TypeHandler<Object> unknownTypeHandler = new UnknownTypeHandler(this);
	  
	  // 记录了全部TypeHandler的类型以及该类型相应的TypeHandler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;


	 public void register(String packageName) {
	    ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<>();
	    //获取packageName包下类型是TypeHandler的类
	    resolverUtil.find(new ResolverUtil.IsA(TypeHandler.class), packageName);
	    Set<Class<? extends Class<?>>> handlerSet = resolverUtil.getClasses();
	    for (Class<?> type : handlerSet) {
	      //类不是匿名类   类不是接口     类不是抽象类
	      if (!type.isAnonymousClass() && !type.isInterface() && !Modifier.isAbstract(type.getModifiers())) {
	        register(type);
	      }
	    }
	  }

	 public void register(Class<?> typeHandlerClass) {
	    boolean mappedTypeFound = false;
	    //类上是否标注了@MappedTypes注解，其用于指定当前类型处理器处理的java类
	    MappedTypes mappedTypes = typeHandlerClass.getAnnotation(MappedTypes.class);
	    if (mappedTypes != null) {
	      for (Class<?> javaTypeClass : mappedTypes.value()) {
	        //将其注册到typeHandlerMap类型处理器池中，
	        //我们可以使用@MappedJdbcTypes注解，表明其该TypeHandler把java类型变成那种jdbctype
	        register(javaTypeClass, typeHandlerClass);
	        mappedTypeFound = true;
	      }
	    }
	    //
	    if (!mappedTypeFound) {
	       //1、判断其是否是TypeReference<T>类型，如果是，获取其T的类型，将其作为该TypeHandler的javaType
	       //如果不是TypeReference<T>类型，那么就不会把其注册到typeHandlerMap中，只会注册到allTypeHandlersMap
	      register(getInstance(null, typeHandlerClass));
	    }
	  }
}

结论：
1、当我们使用package方式注册TypeHandler时，如果我们的TypeHandler没有继承TypeReference<T>类，那么我们就要使用@MappedTypes注解，标准其用于指定处理的java类。否则会报错，如果我们想指定其jdbcType,我们可以使用@MappedJdbcTypes注解
2、当我们使用package方式注册TypeHandler时，如果我们的TypeHandler继承了TypeReference<T>类，那么其处理的java类就是T,如果我们想改变其指定处理的java类，我们可以使用@MappedTypes注解，如果我们想指定其jdbcType,我们可以使用@MappedJdbcTypes注解

案例

  <typeHandlers>
    <package name="com.clyu.config"/>
  </typeHandlers>

Mybatis中有2种枚举类型处理器是他们分别是EnumTypeHandler（用来存储枚举的名称）和EnumOrdinalTypeHandler（用来存储枚举的序数值），其默认枚举类型处理器是EnumTypeHandler

//如果MyEnumCodeTypeHandler只TypeHandler，那么，必须显示用@MappedTypes注解指定javaType
public class MyEnumCodeTypeHandler extends BaseTypeHandler<MyEnum> {
  
  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, MyEnum parameter, JdbcType jdbcType) throws SQLException {
    if (jdbcType == null) {
      ps.setString(i, parameter.getCode());
    } else {
      ps.setObject(i, parameter.getCode(), jdbcType.TYPE_CODE); // see r3589
    }
  }

  @Override
  public MyEnum getNullableResult(ResultSet rs, String columnName) throws SQLException {
    String s = rs.getString(columnName);
    return MyEnum.getMyEnum(s);
  }

  @Override
  public MyEnum getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
    String s = rs.getString(columnIndex);
    return MyEnum.getMyEnum(s);
  }

  @Override
  public MyEnum getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
    String s = cs.getString(columnIndex);
    return MyEnum.getMyEnum(s);
  }
}

2.2 typeHandler注册方式源码分析

typeHandler注册方式有2中情况，一是javaType和handler为空，

<typeHandlers>
    <typeHandler handler="com.clyu.config.MyEnumCodeTypeHandler" javaType="com.clyu.config.MyEnum" jdbcType="int"/>
</typeHandlers>

其原理如下

public final class TypeHandlerRegistry {
  
  public void register(Class<?> javaTypeClass, Class<?> typeHandlerClass) {
    register(javaTypeClass, getInstance(javaTypeClass, typeHandlerClass));
  }
  
  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) {
    MappedJdbcTypes mappedJdbcTypes = typeHandler.getClass().getAnnotation(MappedJdbcTypes.class);
    //从这里可以看出@MappedJdbcTypes注解值会覆盖xml中的jdbcType
    if (mappedJdbcTypes != null) {
      for (JdbcType handledJdbcType : mappedJdbcTypes.value()) {
        register(javaType, handledJdbcType, typeHandler);
      }
      if (mappedJdbcTypes.includeNullJdbcType()) {
        register(javaType, null, typeHandler);
      }
    } else {
     //这里忽略了xml中的jdbcType
      register(javaType, null, typeHandler);
    }
  }
 }

<typeHandlers>
    <typeHandler handler="com.clyu.config.MyEnumCodeTypeHandler"  jdbcType="int"/>
</typeHandlers>

这种方式必须使用@MappedTypes注解指定javaType

其原理如下

public final class TypeHandlerRegistry {
  
 public void register(Class<?> typeHandlerClass) {
	    boolean mappedTypeFound = false;
	    //类上是否标注了@MappedTypes注解，其用于指定当前类型处理器处理的java类
	    MappedTypes mappedTypes = typeHandlerClass.getAnnotation(MappedTypes.class);
	    if (mappedTypes != null) {
	      for (Class<?> javaTypeClass : mappedTypes.value()) {
	        //将其注册到typeHandlerMap类型处理器池中，
	        //我们可以使用@MappedJdbcTypes注解，表明其该TypeHandler把java类型变成那种jdbctype
	        register(javaTypeClass, typeHandlerClass);
	        mappedTypeFound = true;
	      }
	    }
	    //
	    if (!mappedTypeFound) {
	       //1、判断其是否是TypeReference<T>类型，如果是，获取其T的类型，将其作为该TypeHandler的javaType
	       //如果不是TypeReference<T>类型，那么就不会把其注册到typeHandlerMap中，只会注册到allTypeHandlersMap
	      register(getInstance(null, typeHandlerClass));
	    }
}

<typeHandlers>
    <typeHandler handler="com.clyu.config.MyEnumCodeTypeHandler" javaType="com.clyu.config.MyEnum"/>
</typeHandlers>

其原理如下

public final class TypeHandlerRegistry {
  
   public void register(Class<?> javaTypeClass, Class<?> typeHandlerClass) {
   //getInstance方法是获取TypeHandler的对象
    register(javaTypeClass, getInstance(javaTypeClass, typeHandlerClass));
  }
  
  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) {
    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);
    }
  }

 }

三、默认注册的TypeHandler

public final class TypeHandlerRegistry {

  //这里指定了默认的枚举处理器EnumTypeHandler
  private Class<? extends TypeHandler> defaultEnumTypeHandler = EnumTypeHandler.class;

  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(Reader.class, new ClobReaderTypeHandler());
    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 StringTypeHandler());
    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 StringTypeHandler());
    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(InputStream.class, new BlobInputStreamTypeHandler());
    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, unknownTypeHandler);
    register(Object.class, JdbcType.OTHER, unknownTypeHandler);
    register(JdbcType.OTHER, unknownTypeHandler);

    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());

    register(String.class, JdbcType.SQLXML, new SqlxmlTypeHandler());

    register(Instant.class, new InstantTypeHandler());
    register(LocalDateTime.class, new LocalDateTimeTypeHandler());
    register(LocalDate.class, new LocalDateTypeHandler());
    register(LocalTime.class, new LocalTimeTypeHandler());
    register(OffsetDateTime.class, new OffsetDateTimeTypeHandler());
    register(OffsetTime.class, new OffsetTimeTypeHandler());
    register(ZonedDateTime.class, new ZonedDateTimeTypeHandler());
    register(Month.class, new MonthTypeHandler());
    register(Year.class, new YearTypeHandler());
    register(YearMonth.class, new YearMonthTypeHandler());
    register(JapaneseDate.class, new JapaneseDateTypeHandler());

    // issue #273
    register(Character.class, new CharacterTypeHandler());
    register(char.class, new CharacterTypeHandler());
  }
}

Java知识库最新文章

计算距离春节还有多长时间

系统开发系列之WebService（spring框架+ma

springBoot+Cache(自定义有效时间配置)

SpringBoot整合mybatis实现增删改查、分页查

spring教程

SpringBoot+Vue实现美食交流网站的设计与实

加:2021-07-17 11:46:11 更:2021-07-17 11:47:18

360图书馆购物三丰科技阅读网日历万年历 2024年5日历

-2024/5/8 5:34:08-

图片自动播放器
↓图片自动播放器↓

TxT小说阅读器
↓语音阅读,小说下载,古典文学↓

一键清除垃圾
↓轻轻一点,清除系统垃圾↓

图片批量下载器
↓批量下载图片,美女图库↓

网站联系: qq:121756557 email:121756557@qq.com IT数码