java.math.BigInteger cannot be cast to java.lang.L

问题:

I've got List<Long> dynamics. And I want to get max result using Collections. This is my code:

List<Long> dynamics=spyPathService.getDynamics();
        Long max=((Long)Collections.max(dynamics)).longValue(); 

This is my getDynamics:

public List<Long> getDynamics() {

        Session session = null;

        session = this.sessionFactory.getCurrentSession();
        Query query = session
                .createSQLQuery("SELECT COUNT(*) FROM SpyPath WHERE DATE(time)>=DATE_SUB(CURDATE(),INTERVAL 6 DAY) GROUP BY DATE(time) ORDER BY time;");

        List<Long> result = query.list();
        return result;

    }

Now I'm getting java.math.BigInteger cannot be cast to java.lang.Long. What's wrong?

回答1:

Your error might be in this line:

List<Long> result = query.list();

where query.list() is returning a BigInteger List instead of Long list. Try to change it to.

List<BigInteger> result = query.list();

回答2:

Better option is use SQLQuery#addScalar than casting to Long or BigDecimal.

Here is modified query that returns count column as Long

Query query = session
             .createSQLQuery("SELECT COUNT(*) as count
                             FROM SpyPath 
                             WHERE DATE(time)>=DATE_SUB(CURDATE(),INTERVAL 6 DAY) 
                             GROUP BY DATE(time) 
                             ORDER BY time;")
             .addScalar("count", LongType.INSTANCE);

Then

List<Long> result = query.list(); //No ClassCastException here  

Related link

• Hibernate javadocs
• Scalar queries
• Hibernate.LONG, remember it has been deprecated since Hibernate version 3.6.X
  here is the deprecated document, so you have to use LongType.INSTANCE
• My previous answer

回答3:

Try to convert the BigInteger to a long like this

Long longNumber= bigIntegerNumber.longValue();

回答4:

I'm lacking context, but this is working just fine:

List<BigInteger> nums = new ArrayList<BigInteger>();
Long max = Collections.max(nums).longValue(); // from BigInteger to Long...

回答5:

You need to add an alias for the count to your query and then use the addScalar() method as the default for list() method in Hibernate seams to be BigInteger for numeric SQL types. Here is an example:

List<Long> sqlResult = session.createSQLQuery("SELECT column AS num FROM table")
    .addScalar("num", StandardBasicTypes.LONG).list();

回答6:

Are you sure dynamics is a List<Long> and not List<BigInteger> ?

If dynamics is a List<Long> you don't need to do a cast to (Long)

回答7:

Imagine d.getId is a Long, then wrap like this:

BigInteger l  = BigInteger.valueOf(d.getId());