我如何在JDBC中从resultSet读取可能为空的double值？ [英] How do I in JDBC read a possibly null double value from resultSet?

问题描述

我的数据库中有一列，键入 double ，我想使用JDBC ResultSet读取它的值，但可能为null。这样做最好的方法是什么？我可以想到三个选项，其中没有一个似乎非常好。

选项1：因为异常处理冗长和臭味

  double d; 
 try {
 d = rs.getDouble（1）; 
 //做某事
} catch（SQLException ex）{
 if（rs.wasNull（））{
 // do something else 
} else {
 throw ex; 
} 
} 
  

选项2：由于两次提取

  s = rs.getString（1）; //或getObject（）
 if（s == null）{
 // do something else 
} else {
 double d = rs.getDouble（1）; 
 //做某事
} 
  

选项3：错误，因为Java而不是SQL转换

  s = rs.getString（1）; //或getObject（）
 if（s == null）{
 // do something else 
} else {
 double d = Double.parseDouble（s）; 
 //做某事
} 
  

任何建议，哪种方式更好，还是有另一个优越的方式？请不要说使用Hibernate，我仅限于JDBC代码。

解决方案

选项1最接近：

  double d = rs.getDouble（1）; 
 if（rs.wasNull（））{
 // do something 
} else {
 // use d 
} 
  

这不是很好，但这是JDBC。如果列为空，则双重值被认为是坏，所以每次读取数据库中为空的原语时，应该使用 wasNull（） / p>

I have a column in my database that is typed double and I want to read the value from it using a JDBC ResultSet, but it may be null. What is the best way of doing this? I can think of three options none of which seem very good.

Option 1: Bad because exception handling verbose and smelly

double d;
try {
   d = rs.getDouble(1);
   // do something
} catch(SQLException ex) {
   if(rs.wasNull()) {
      // do something else
   } else {
     throw ex;
   }
}

Option 2: Bad because two fetches

s = rs.getString(1); // or getObject()
if(s == null) {
  // do something else
} else {
  double d = rs.getDouble(1);
  // do something
}

Option 3: Bad because Java rather than SQL conversion

s = rs.getString(1); // or getObject()
if(s == null) {
  // do something else
} else {
  double d = Double.parseDouble(s);
  // do something
}

Any suggestions on which way is better, or is there another superior way? And please don't say "Use Hibernate", I'm restricted to JDBC code only here.

解决方案

Option 1 is closest:

double d = rs.getDouble(1);
if (rs.wasNull()) {
  // do something
} else {
  // use d
}

It's not very nice, but that's JDBC. If the column was null, the double value is considered "bad", so you should check using wasNull() every time you read a primitive that is nullable in the database.

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