Mybatis之TypeHandler | 易学教程

mybatis-3.4.6.release.

TypeHandler在mybatis中是个重要的组件，对statement设置参数还是从Resultset中取值，都会用到它。

List-1

public interface TypeHandler<T> {

  void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;

  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List-1中所示，setParameter方法在ParameterHandler中使用到，其它三个getResult方法在ResultSetHandler中使用到，为什么会有三个getResult方法是因为从ResultSet中获取值，可以通过下标或列名称获取，此外存储过程的处理方式不同。

图1

BaseTypeHandler的类继承图如图1所示，先来看下TypeReferernce，其作用主要是获取类上的泛型，在TypeReferernce的构造方法中实现的，如下List-2所示，getRawType的结果是BigDecimal.

List-2

public class BigDecimalTypeHandler extends BaseTypeHandler<BigDecimal>

BaseTypeHandler中使用了模板模式，具体实现由子类来实现，如下List-3:

List-3

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 {
      ...
      如果parameter是null，则直接调用PreparedStatement的setNull方法
      ps.setNull(i, jdbcType.TYPE_CODE);
      ...
      setNonNullParameter(ps, i, parameter, jdbcType);
      ...
  }

  @Override
  public T getResult(ResultSet rs, String columnName) throws SQLException {
      ...
      result = getNullableResult(rs, columnName);
      ...
  }

  @Override
  public T getResult(ResultSet rs, int columnIndex) throws SQLException {
      ...
      result = getNullableResult(rs, columnIndex);
      ...
  }

  @Override
  public T getResult(CallableStatement cs, int columnIndex) throws SQLException {
      ...
      result = getNullableResult(cs, columnIndex);
      ...
  }

  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;

}

来看个例子BooleanTypeHandler:

List-4

public class BooleanTypeHandler extends BaseTypeHandler<Boolean> {

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

  @Override
  public Boolean getNullableResult(ResultSet rs, String columnName)
      throws SQLException {
    return rs.getBoolean(columnName);
  }

  @Override
  public Boolean getNullableResult(ResultSet rs, int columnIndex)
      throws SQLException {
    return rs.getBoolean(columnIndex);
  }

  @Override
  public Boolean getNullableResult(CallableStatement cs, int columnIndex)
      throws SQLException {
    return cs.getBoolean(columnIndex);
  }
}

Reference

https://github.com/mybatis/mybatis-3/tree/3.4.x

来源：oschina

链接：https://my.oschina.net/u/2518341/blog/3119789

标签

外存

MyBatis