How do I in JDBC read a possibly null double value from resultSet?

问题

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.

回答1:

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.

回答2:

Depending on your JDBC driver and database, you may be able to use a boxed type and cast:

Double doubleValueOrNull = (Double)rs.getObject(1); // or .getObject("columnName")

It will be null if the column was NULL.

Be careful to check this still works if you change database.

回答3:

Use:

rs.getObject(1)==null?null:rs.getBigDecimal(1).doubleValue()

回答4:

Or with java 8 you can do this:

Double dVal = Optional.ofNullable(resultSet.getBigDecimal("col_name"))
                .map(BigDecimal::doubleValue).orElse(null));

回答5:

Kotlin version to retrieve a nullable field:

val parentId = resultSet.getObject("parent_id") as Double?

来源：https://stackoverflow.com/questions/1103460/how-do-i-in-jdbc-read-a-possibly-null-double-value-from-resultset

标签

java

jdbc

null

double