mybatis-type 类型包解析

概述

类型包是mybatis提供类型转换处理的包，mybatis提供了许多基本类型处理器的实现。在javaType和jdbcType之间转换时所用到。

TypeHandler

本包的重点类，类型处理器

public interface TypeHandler<T> {

  // 往Statement中设置参数，javaType 转 jdbcType
  void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;

  // 返回值转换，jdbcType 转 javaType
  T getResult(ResultSet rs, String columnName) throws SQLException;

  // 返回值转换，jdbcType 转 javaType
  T getResult(ResultSet rs, int columnIndex) throws SQLException;

  // 返回值转换，jdbcType 转 javaType（存储过程）
  T getResult(CallableStatement cs, int columnIndex) throws SQLException;

}

TypeHandler这里的type指的是javaType，你需要对一个指定的一个javaType编写TypeHandler。

BaseTypeHandler

Base类，典型的模板方法模式，实现了TypeHandler的方法，将异常捕获、null值处理的通用逻辑做了处理，具体真正的转换逻辑留给子类实现。

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

  @Override
  public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
    //处理参数为null
    if (parameter == null) {
      if (jdbcType == null) {
        throw new TypeException("JDBC requires that the JdbcType must be specified for all nullable parameters.");
      }
      try {
        ps.setNull(i, jdbcType.TYPE_CODE);
      } catch (SQLException e) {
        throw new TypeException("Error setting null for parameter #" + i + " with JdbcType " + jdbcType + " . "
              + "Try setting a different JdbcType for this parameter or a different jdbcTypeForNull configuration property. "
              + "Cause: " + e, e);
      }
    } else {
      // 参数不为null 留给子类实现
      try {
        setNonNullParameter(ps, i, parameter, jdbcType);
      } catch (Exception e) {
        throw new TypeException("Error setting non null for parameter #" + i + " with JdbcType " + jdbcType + " . "
              + "Try setting a different JdbcType for this parameter or a different configuration property. "
              + "Cause: " + e, e);
      }
    }
  }

  /**
   * 通过columnName从resultSet中取值，
   * 转换的类型根据子类来实现转换
   * @param rs
   * @param columnName Colunm name, when configuration useColumnLabel is false
   * @return
   * @throws SQLException
   */
  @Override
  public T getResult(ResultSet rs, String columnName) throws SQLException {
    try {
      return getNullableResult(rs, columnName);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column '" + columnName + "' from result set.  Cause: " + e, e);
    }
  }

  @Override
  public T getResult(ResultSet rs, int columnIndex) throws SQLException {
    try {
      return getNullableResult(rs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column #" + columnIndex + " from result set.  Cause: " + e, e);
    }
  }
  
  @Override
  public T getResult(CallableStatement cs, int columnIndex) throws SQLException {
    try {
      return getNullableResult(cs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column #" + columnIndex + " from callable statement.  Cause: " + e, e);
    }
  }

  // 抽象方法，子类实现
  
  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;

}

TypeReference

为了获取泛型类的真实类型，通过ParameterizedType.getActualTypeArguments()[0]的方式获取<>中的类型。

public abstract class TypeReference<T> {

  private final Type rawType;

  protected TypeReference() {
    rawType = getSuperclassTypeParameter(getClass());
  }

  Type getSuperclassTypeParameter(Class<?> clazz) {

    //获取父类的type
    Type genericSuperclass = clazz.getGenericSuperclass();

    //如果父类是Class类型，则继续往上递归
    if (genericSuperclass instanceof Class) {
      // try to climb up the hierarchy until meet something useful
      if (TypeReference.class != genericSuperclass) {
        return getSuperclassTypeParameter(clazz.getSuperclass());
      }

      throw new TypeException("'" + getClass() + "' extends TypeReference but misses the type parameter. "
        + "Remove the extension or add a type parameter to it.");
    }

    // 当父类的类型是ParameterizedType（泛型类）时，通过getActualTypeArguments获取泛型的类型
    Type rawType = ((ParameterizedType) genericSuperclass).getActualTypeArguments()[0];
    // TODO remove this when Reflector is fixed to return Types
    if (rawType instanceof ParameterizedType) {
      rawType = ((ParameterizedType) rawType).getRawType();
    }

    return rawType;
  }

  public final Type getRawType() {
    return rawType;
  }

  @Override
  public String toString() {
    return rawType.toString();
  }
}

有关ParameterizedType的知识，ParameterizedType详解

IntegerTypeHandler

看一个类型的真实实现类。

public class IntegerTypeHandler extends BaseTypeHandler<Integer> {

  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, Integer parameter, JdbcType jdbcType)
      throws SQLException {
    ps.setInt(i, parameter);
  }

  @Override
  public Integer getNullableResult(ResultSet rs, String columnName)
      throws SQLException {
    int result = rs.getInt(columnName);
    return result == 0 && rs.wasNull() ? null : result;
  }

  @Override
  public Integer getNullableResult(ResultSet rs, int columnIndex)
      throws SQLException {
    int result = rs.getInt(columnIndex);
    return result == 0 && rs.wasNull() ? null : result;
  }

  @Override
  public Integer getNullableResult(CallableStatement cs, int columnIndex)
      throws SQLException {
    int result = cs.getInt(columnIndex);
    return result == 0 && cs.wasNull() ? null : result;
  }
}

Integer实现类，够简单直接把。typeHandler就这么easy。

TypeHandlerRegistry

类型处理器说完了，该怎么用呢?这就要靠类型处理器注册器了，提前把类型处理器放进去，需要使用的时候从里面拿就可以了。

public final class TypeHandlerRegistry {

  /**
   * jdbc类型处理器容器
   */
  private final Map<JdbcType, TypeHandler<?>>  jdbcTypeHandlerMap = new EnumMap<>(JdbcType.class);

  /**
   * java 类型处理器容器
   key:javaType
   value:Map
   * 这里为什么value还是个map，jdbctype和typehandler的映射，
   * 因为mybatis提供了MappedJdbcTypes注解，对TypeHandler指定jdbcType
   * 因此在注册javaType的TypeHandler时也需考虑jdbcType的指定，不过一般情况通常是null
   * 即 Map这里的jdbcType为null
   */
  private final Map<Type, Map<JdbcType, TypeHandler<?>>> typeHandlerMap = new ConcurrentHashMap<>();
  /**
  * 位置类型处理器
  */
  private final TypeHandler<Object> unknownTypeHandler;
  /**
  *  key:  TypeHandler的class
  *  value:TypeHandler 
  */
  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;
}

TypeHandlerRegistry的属性主要是不同维度的HashMap。

可以通过jdbcType查找、也可以通过javaType查找。

public TypeHandlerRegistry(Configuration configuration) {
  this.unknownTypeHandler = new UnknownTypeHandler(configuration);

  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());
}

构造函数内默认注册了 基本类型的类型处理器，基本上也够用了。

Alias

mybatis的别名机制也放在type包下，首先是Alias注解

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Alias {
  /**
   * Return the alias name.
   *
   * @return the alias name
   */
  String value();
}

没什么特别，value代表别名

TypeAliasRegistry

先说结论

private final Map<String, Class<?>> typeAliases = new HashMap<>();

key：别名

value：Class对象

public TypeAliasRegistry() {
  registerAlias("string", String.class);

  registerAlias("byte", Byte.class);
  registerAlias("long", Long.class);
  registerAlias("short", Short.class);
  registerAlias("int", Integer.class);
  registerAlias("integer", Integer.class);
  registerAlias("double", Double.class);
  registerAlias("float", Float.class);
  registerAlias("boolean", Boolean.class);

  registerAlias("byte[]", Byte[].class);
  registerAlias("long[]", Long[].class);
  registerAlias("short[]", Short[].class);
  registerAlias("int[]", Integer[].class);
  registerAlias("integer[]", Integer[].class);
  registerAlias("double[]", Double[].class);
  registerAlias("float[]", Float[].class);
  registerAlias("boolean[]", Boolean[].class);

  registerAlias("_byte", byte.class);
  registerAlias("_long", long.class);
  registerAlias("_short", short.class);
  registerAlias("_int", int.class);
  registerAlias("_integer", int.class);
  registerAlias("_double", double.class);
  registerAlias("_float", float.class);
  registerAlias("_boolean", boolean.class);

  registerAlias("_byte[]", byte[].class);
  registerAlias("_long[]", long[].class);
  registerAlias("_short[]", short[].class);
  registerAlias("_int[]", int[].class);
  registerAlias("_integer[]", int[].class);
  registerAlias("_double[]", double[].class);
  registerAlias("_float[]", float[].class);
  registerAlias("_boolean[]", boolean[].class);

  registerAlias("date", Date.class);
  registerAlias("decimal", BigDecimal.class);
  registerAlias("bigdecimal", BigDecimal.class);
  registerAlias("biginteger", BigInteger.class);
  registerAlias("object", Object.class);

  registerAlias("date[]", Date[].class);
  registerAlias("decimal[]", BigDecimal[].class);
  registerAlias("bigdecimal[]", BigDecimal[].class);
  registerAlias("biginteger[]", BigInteger[].class);
  registerAlias("object[]", Object[].class);

  registerAlias("map", Map.class);
  registerAlias("hashmap", HashMap.class);
  registerAlias("list", List.class);
  registerAlias("arraylist", ArrayList.class);
  registerAlias("collection", Collection.class);
  registerAlias("iterator", Iterator.class);

  registerAlias("ResultSet", ResultSet.class);
}

内置别名，在编写mybatis的动态sql时都可以使用。

public void registerAlias(Class<?> type) {
  String alias = type.getSimpleName();
  Alias aliasAnnotation = type.getAnnotation(Alias.class);
  if (aliasAnnotation != null) {
    alias = aliasAnnotation.value();
  }
  registerAlias(alias, type);
}

 public void registerAlias(String alias, Class<?> value) {
    if (alias == null) {
      throw new TypeException("The parameter alias cannot be null");
    }
    // issue #748
    String key = alias.toLowerCase(Locale.ENGLISH);
    if (typeAliases.containsKey(key) && typeAliases.get(key) != null && !typeAliases.get(key).equals(value)) {
      throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + typeAliases.get(key).getName() + "'.");
    }
    typeAliases.put(key, value);
  }

如果是直接通过类型注册，那么别名就取类的名字的小写。知道一下就好。

总结

Type包很纯粹，就是为了处理类型转换，为了类型查找、使用方便增加了别名机制。顺道复习了一下模板方式模式。

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That’s All