是否可以将基本的JDBC SQL类型映射到Java类? [英] Is it possible to map basic JDBC SQL types to a Java class?

问题描述

使用getObject方法从ResultSet对象检索列时，该类由JDBC驱动程序选择.我正在寻找一种选择在运行时检索列的类的方法.

When retrieving a column from a ResultSet object using the getObject method, the class is chosen by the JDBC driver. I am looking for a way to choose which class the column is retrieved as at runtime.

在下面的示例中，使用变量T作为整数创建类型Class1.

In the example below type Class1 is created with variable T as an Integer.

Class Class1<T>
{
  public T getColumn(DataSource ds)
  {
    T value = null;
    Connection con = null;

    try
    {
      con = ds.getConnection();
      Statement st = con.createStatement();
      ResultSet rs = st.executeQuery("select 1 from dual");
      rs.next();
      Object o = rs.getObject(1); // I want an Integer but a BigDecimal is created!
      value = (T) o; // ClassCastException here!
      rs.close();
      st.close();
    }
    finally
    {
      if (con != null) { con.close(); }
    }

    return i;
  }
}

ResultSet类提供了一个名为getObject的方法，该方法接受列参数和Map类型的参数.映射类型仅用于UDT(用户定义类型).我还需要将此功能应用于基本SQL类型.我知道我可以使用switch/case语句来实现此目的的解决方案，但我正努力避免这种情况.这可能吗?

The ResultSet class provides a method called getObject that accepts a column argument and a type Map argument. This type Map is only used for UDT (user defined types). I need this functionality applied to basic SQL types as well. I know I can implement a solution to this using a switch/case statement but I'm trying to avoid that. Is this possible?

编辑

我应该提到我在Java 1.6上.看来这可能已在1.7中解决.感谢JB Nizet提供参考.

I should've mentioned I am on Java 1.6. It looks like this may have been solved in 1.7. Thanks JB Nizet for the reference.

推荐答案

JB Nizet提供了Java 1.7的答案:

JB Nizet has provided the answer for Java 1.7: http://docs.oracle.com/javase/8/docs/api/java/sql/ResultSet.html#getObject-int-java.lang.Class-

对于Java的早期版本，DolphinJava是正确的.我将不得不编写自己的代码.

For earlier versions of Java, DolphinJava is correct. I will have to write my own code.

我如何解决

使用上面的示例使用 Class1 ，我创建了扩展 Class1 的子类，其中T是所需的类型，然后制作了特定于类型的方法来调用getColumn Class1 中的方法:

Keeping with my example above using Class1, I created sub-classes that extend Class1 with T being the type needed and then made type-specific methods that call the getColumn method in Class1:

public Class1<T>
{
  public Object getColumn(DataSource ds)
  {
    Object o        = null;
    Connection con  = null;

    try
    {
      con           = ds.getConnection();
      Statement st  = con.createStatement();
      ResultSet rs  = st.executeQuery("select 1 from dual");
      rs.next();
      Object o      = rs.getObject(1);
      rs.close();
      st.close();
    }
    finally
    {
      if (con != null) { con.close(); }
    }

    return o;
  }
}

Class1Integer extends Class1<Integer>
{
  public Integer getIntegerColumn()
  {
    Object o  = getColumn(datasource);
    Integer i = new Integer(o);
    return i;
  }
}

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