I'm trying to create a feed management system. I have created a simple get and post request for the servlet. I'm able to store the data in the datastore successfully as milliseconds.
But when I retrieve it
long milliseconds = entity.getProperty("timestamp");
I get some error like this
java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long
What will be the reason for this issue?
Well, apparently in
long milliseconds = entity.getProperty("timestamp");
entity returns a String, which you assign to a long. This requires a typecast.
Note that Entity (or its superclass, PropertyContainer) explicitly states
The value returned may not be the same type as originally set via setProperty
So - what to do? If you know that you're getting a String, and you want to interpret it as a long: Use the proper conversion method (which is not a typecast).
long longValue = Long.parseLong(stringValue);
...but prepare for NumberFormatExceptions in cases where you convert actual, non-numeric Strings.
Apparently, you are trying to retrieve a String of number format which you want to cast to a long value. The first thing you will have to do is to check whether the value obtained from entity.getProperty("timestamp") returns a number. There's is a special library called Apache Commons Lang 3 that allows to check if your string is of numeric format. If it's the case, then it's a simple implicit cast to long value that you should do. Your code should look as follows,ASSUMING ENTITY IS NOT NULL:
import org.apache.commons.lang3.math.NumberUtils;
if(NumberUtils.isCreatable(entity.getProperty("timestamp")){
long milliseconds = Long.parseLong(entity.getProperty("timestamp"));
}
else{
//print the information you want to identify the value of the property
//for example:
System.out.println("The following value cannot be parsed to long : " +
entity.getProperty("timestamp"));
}
NumberUtils.isCreatable returns true, you need to call NumberUtils.create(...).