How to convert List

Question

I am getting list of Address objects from the DB call.

ArrayList<Address> addresses = new ArrayList<>();

Each Address has an int addressId property.

I am writing an update query where in the IN clause I am sending this whole list of Address objects and I am getting ibatis TypeException. How can I convert List<Address> to a comma separated string which can be sent to update query?

My update query looks like:::

Update tablename set postcode = #{postCode} where id in #{addressID}.

Consider this approach again. In particular, read about SQL injection. — Henry, Feb 04 '18 at 05:53
@Henry Converting into string and sending in IN clause will not solve the problem?I dont know how to pass list in update query.. — user9193174, Feb 04 '18 at 06:22
It will solve this problem but create a new one (a security vulnerability). — Henry, Feb 04 '18 at 06:24
@Henry Creating a new one means.Sorry i did not understood.. — user9193174, Feb 04 '18 at 07:43
I don't see how SQL injection is possible in this case. There is no user input that can affect the creation of the `addressID` string in any way, and `addressId` field has an integer type. — Kirill Simonov, Feb 06 '18 at 07:01

score 57 · Answer 1 · answered Feb 04 '18 at 05:51

57

Using Java 8 you could do it in one line:

String addressID = addresses
           .stream()
           .map(a -> String.valueOf(a.addressId))
           .collect(Collectors.joining(","));

answered Feb 04 '18 at 05:51

Kirill Simonov

8,257
3
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4

a non "List" example!! Thank you ! – granadaCoder Apr 05 '19 at 16:31
and if `addresses` is null? – Johnny Dec 07 '21 at 22:14

mohsenJsh · Answer 2 · 2020-06-08T10:21:42.293

16

for converting to comma seperated String use something like this:

String commaSeparatedStr = addresses
        .stream()
        .map(String::valueOf)
        .collect(Collectors.joining(","));

edited Jun 08 '20 at 10:21

answered Feb 04 '18 at 05:51

mohsenJsh

2,048
3
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49

3

In case someone need a comma separated of variable inside Address object, use the getter inside map `.map(c -> String.valueOf(c.getName()))` – Roy Ryando Jan 10 '20 at 04:26

score 8 · Answer 3 · answered Feb 04 '18 at 05:58

String#join, which accepts delimiter String and Iterable elements (which is List in your case)

 List<String> strings = new LinkedList<>();
 strings.add("Java");
 strings.add("is");
 strings.add("cool");
 String message = String.join(",", strings); //pass delimiter and List
 //message returned is: "Java,is,cool"

score 3 · Answer 4 · answered Feb 04 '18 at 05:51

3

Iterate over the address objects, retrieve their ID and create a String. Something like this:

StringBuilder sb = new StringBuilder();

for (Address a: adresses) {
  sb.append(a.getId());
  sb.append(", ");
}

String ids = sb.toString();

answered Feb 04 '18 at 05:51

Marit

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score 2 · Answer 5 · answered May 08 '20 at 04:52

2

String.join(", ", addresses) ;

answered May 08 '20 at 04:52

Usman

949
9
12

Super simple. Super good. – chendu Oct 20 '22 at 14:01

score 1 · Answer 6 · answered Feb 04 '18 at 05:51

StringBuilder addressIds = new StringBuilder("");
for(Address address : addresses){
  if (addressIds.length() > 1)  
    addressIds.append(", ");
  addressIds.append("'").append(address.id()).append("'");
}

//in this method you can directly send the string in Update tablename + set postcode + where id in <String>.
methodOfUpdateInQuery(addressIds.toString());

score 1 · Answer 7 · answered Feb 04 '18 at 07:04

1

The format required can be obtained using toString() and replaceAll() methods (using regular Expressions).

String addressString = addresses.toString().replaceAll("[ \\[ \\] ]", "");

answered Feb 04 '18 at 07:04

Nithin

748
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27

score 1 · Answer 8 · answered Sep 10 '19 at 21:42

1

List of int - let Java do it:

String tmp = addresses.toString();
String csList = tmp.substring(1, tmp.length()-1);

answered Sep 10 '19 at 21:42

xavierz

335
1
11

8 Answers8