How to get List<String> from List<Object[]> by converting first element of array to String

Question

How to get List<String> from List<Object[]> by converting the first element of array to String?

I tried writing like below but casting is not happening,

List<String> results = query.getResultList()
.stream()
.map(result ->{
 Object[]  temp =  (Object[]) result;
 return temp[0].toString();
})
.collect(Collectors.toList());

Below image shows type of results list I am getting Error:java: incompatible types: java.lang.Object cannot be converted to java.util.List. How to do this correctly using Java 8?

Back up two steps here. First, what is the precise result of getResultList()? Second, what framework are you using to do these queries (JPA, Hibernate), and can you use a type-safe approach? — Makoto
– Makoto, Commented Jan 21, 2016 at 19:06
If you want a list why are you returning only the first element? Groovy? — kpie
– kpie, Commented Jan 21, 2016 at 19:06
What do you mean "casting is not happening"? What is happening? — Tunaki
– Tunaki, Commented Jan 21, 2016 at 19:06
Why do you query multiple fields if you just want one? What's the query? — JB Nizet
– JB Nizet, Commented Jan 21, 2016 at 19:10

Mrinal · Accepted Answer · 2016-01-21 20:04:07Z

16

query.getResultList() returns raw List. As mentioned by @Makoto in comment, try to use type-safe API. But if you intend to use the current API, add type casting (which will generate warning though).

List<String> results = ((List<Object[]>) query.getResultList())
.stream()
.map(result -> result[0].toString())
.collect(Collectors.toList());

answered Jan 21, 2016 at 20:04

Mrinal

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