How to Convert HashSet of Integers to Comma Separated String in Java

Question

I want to convert a HashSet of Integer to Comma Separated String,

so I can use the same in where clause of a MySQL query.

//[MySQL - Sample table Schema]
my_table
state_id INTEGER
shop_id INTEGER

Set<Integer> uniqueShopIds = shopService.GetShopIds(); // This returns HashSet<Integer>
String inClause = ; // **How do i convert the uniqueShopIds to comma separated String**
String selectQuery = String.format("SELECT DISTINCT(state_id) FROM my_table WHERE shop_id IN (%s);", inClause);

If there's any other way, I can use the HashSet directly in IN CLAUSE of the PreparedStatment, please share.

@azro thanks, but i want to convert set of integers to comma separated string, for set of strings, i had worked it out already. — Manikandaraj Srinivasan, May 27 '20 at 21:23

score 7 · Accepted Answer · answered May 27 '20 at 21:13

7

Set<Integer> s = new HashSet<>(Arrays.asList(1, 2, 3));
String str = s.stream().map(Object::toString).collect(Collectors.joining(","));
System.out.println(str); // prints 1,2,3

answered May 27 '20 at 21:13

Mark Bramnik

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Thank you @Mark Bramnik – Manikandaraj Srinivasan May 27 '20 at 21:21

score 0 · Answer 2 · answered May 28 '20 at 01:15

Then there is this.

Set<Integer> s = new HashSet<>(Arrays.asList(1, 2, 3));

The default toString for a collection is a csv surrounded by []

So skip the first one and remove the last one

String str = s.toString().substring(1).replace("]","");

Or just take the substring in between

String str = s.toString();
str = str.substring(1,str.length()-1);

System.out.println(str);

Both would result in

1, 2, 3

How to Convert HashSet of Integers to Comma Separated String in Java

2 Answers2