MyBatis 插入空值时，需要指定JdbcType

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看一看 org.apache.ibatis.type.BaseTypeHandler

@Override  public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {    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 {      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);      }    }  }

子类 BigIntegerTypeHandler 对 setNonNullParameter 的实现如下：

@Override  public void setNonNullParameter(PreparedStatement ps, int i, BigInteger parameter, JdbcType jdbcType) throws SQLException {    ps.setBigDecimal(i, new BigDecimal(parameter));  }

可以看出，当参数的值为 NULL，且没有指定 jdbcType 时，mybatis会抛出 “JDBC requires that the JdbcType must be specified for all nullable parameters.” 异常。

而当参数不为 NULL 时，Mybatis 会针对参数自身的类型调用 PreparedStatement 上不同的方法，此时 JdbcType 则是可以省略的。

再看 JDBC 中PreparedStatement 的 setNull 方法就不难明白，JDBC 要求我们设置 NULL 参数时必须指定 JDBC 类型，Mybatis 只是照章办事而已。

void setNull(int parameterIndex,             int sqlType)             throws SQLExceptionSets the designated parameter to SQL NULL.Note: You must specify the parameter's SQL type.Parameters:parameterIndex - the first parameter is 1, the second is 2, ...sqlType - the SQL type code defined in java.sql.TypesThrows:SQLException - if parameterIndex does not correspond to a parameter marker in the SQL statement; if a database access error occurs or this method is called on a closed PreparedStatementSQLFeatureNotSupportedException - if sqlType is a ARRAY, BLOB, CLOB, DATALINK, JAVA_OBJECT, NCHAR, NCLOB, NVARCHAR, LONGNVARCHAR, REF, ROWID, SQLXML or STRUCT data type and the JDBC driver does not support this data type

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