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REST - Download list of users

Context:
I want to write an endpoint that will return a Collection of users based on their usernames. How should those username be passed to the REST endpoint - note that I can (potentially) have a lot of usernames (say > 5000)?
Solution #1:
Use a GET endpoint, concatenate the usernames on client side and pass them as a single request parameter. Split the request parameter on server side to get the list of usernames.
#RestController
public class UserController {
#GetMapping
// able to deserialize `filename1,filename2` to List out of the box
public Collection<User> getUser(#RequestParam List<String> usernames) {
return userService.getUsersByUsername(usernames);
}
}
Solution #2:
Use a POST endpoint and pass the list of usernames as request body. Although cleaner form a coding perspective, I end up using a POST to fetch data.
#RestController
public class UserController {
#PostMapping
public Collection<User> getUser(#RequestBody List<String> usernames) {
return userService.getUsersByUsername(usernames);
}
}
Questions:
Which of the two solutions would be the better approach?
Do you have a better approach to pass the list of usernames into the endpoint?
Edits:
I've updated the signature of the first solution based on suggestions from answers. Spring is able to deserialize filename1,filename2 to List out of the box for #RequestParam.

POST looks like a cleaner approach in this case because -
Sending a huge string in a URL is not a good idea and there is scope for error
You need to write additional code (logic) to create the string on frontend and split it on backend.
Sending a huge string in a URL is not scalable as there are limits on the length of URL.

Get approach might result into an issue since URL length is limited and then you have to limit your query parameters.
Though its not a post request but in your case i think post is the only way out.

I would agree with all the answers given above. I would like to specify one more point , if you are going with post request you might have to increase the payload capacity a server can receive , the default post capacity(The maximum size in bytes) of spring boot is 2mb (based on your server). While testing your code might work fine with 1000-2000 usernames but make sure to change the property to accept more bytes in request.

GET is not limited, yet the browser is. Your server client does not seem to be the browser, so I would say GET is the way to go.
P.S GET can receive a body (not so great, but POST is not also the best match).
You don need to concatenated the string and add extra computation on server server, GET can receive a list of separate strings.
UPDATE with example:
#RestController
public class MyController {
#GetMapping(value = "/test")
public List<String> getTestParams(#RequestParam List<String> params) {
return params;
}
}
The test with 3000 params
#RunWith(SpringRunner.class)
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class TestMyController {
#Autowired
private TestRestTemplate restTemplate;
#Test
public void testRequestWithParamsList() {
List<String> params = new ArrayList<>();
for (int i = 0; i < 3000; i++) {
params.add(String.valueOf(i));
}
List<String> result = restTemplate.getForObject(buildUrl(params),
List.class);
assertEquals(params, result);
}
private String buildUrl(List<?> params) {
return "/test?params=" + getUrlParameter(params);
}
private String getUrlParameter(List<?> params) {
return params.stream()
.map(Object::toString)
.collect(Collectors.joining(","));
}
}
If you are using tomcat you must specify also the max http header property in application.properties
server.max-http-header-size=30000

Validating Query Params in REST API

I have a REST API which accepts query parameters. The query parameters are valid if and only if at a time only one query parameter is passed and it is among the list of valid query parameters.
Currently my logic for this is:
I am collecting the query params in a map. And then checking it's size. If size > 1 function throwing an error. If that is not the case then iterating through the map and if find a parameter other than valid ones the function throwing an error.
For example:
if(queryParam.size()>1) {
throw new FailureResponse();
}
queryParam.forEach(e->{
String key = e.getKey();
if(!key.equalsIgnoreCase("p1") && !key.equalsIgnoreCase("p2")) {
throw new FailureResponse();
}
});
But I think in this way I am violating the SOLID design principle which says a class should be open for extension but closed for modification.
I also thought of creating a file and then reading the acceptable params from it but that would add to the response time of the API as it involves reading a file.
Is there some way I can keep and read the valid query-params and it does not violate the design principles?

You could maintain an Enum of valid params and extend the enums as and when applicable like
public enum QueryParams{
PARAM_1("param1"),
PARAM_2("param2"),
private String paramValue;
QueryParams(String paramName){
this.paramValue = paramValue();
}
public void getParamValue(){
return this.value;
}
}
and then you could iterate over the set of values of this enum to filter out invalid values
List<String> validParams = Arrays.asList(QueryParams.values()).stream().map(QueryParams::getParamValue).collect(Collectors.toList());
queryParams.removeAll(validParams);
if(queryParams.size()!=0) {
throw new FailureResponse();
}
}
This helps you maintain the API class without any changes, whenever a new parameter is added, just extend the enum and all the rest is automatically extended as it all depends upon the value in the enum.

Validate if one field is present and valid

I just wanted to know how custom validation or any other solution would be implemented on a POJO. My POJO has been used in many ways where i do not need any kind of validation such as #NotBlank etc. However there is a scenario if i want to update at least one field inside it. Then validate it.
My POJO is provided in the request body and i want to validate if one of the field is provided then accept the request else don't. So far i have implemented it in a hard coded way. But i would like something which spring boot provides.
My pojo is below
public class Person {
private String name;
private String age;
private String email;
//etc .etc. getters and setters
}
Now if i want to update a person i want to validate if a single field is provided in the Request Body then accept the payload else throw constraint violation.
So far i have done it hard coded ie
private boolean isInValid(Person per) {
if (per == null) {
return true;
}
int changes = 0;
changes = changes + (StringUtils.isBlank(per.getName()) ? 0 : 1);
changes = changes + (StringUtils.isBlank(per.getEmail()) ? 0 : 1);
//etc etc...
return changes == 0;
}
I would like something that spring boot provides.
thanks

If it is not enough standard Hibernate Validator checks, you can implement your own validators using your custom logic

Is there a simple class that encapsulates a Boolean and a String?

It is so common in UI logic that you have a method to checkValid(something). Its primary use is to return a Boolean. But in case of invalid (or false), we may want to provide an additional user message about what is being invalid, after all the checkValid() method might have checked 20 different things. By simply responding with "not valid" to the user is not very helpful.
So is there a built-in Java class or some from Apache commons that does just that? I understand it is so simple to build my own, but my sense tells me this is so common I must missed it somewhere in common packages.

Status codes have long been used to return "Success" (often 0) or "Failure" responses, with failures further identified by distinct non-zero values. The Enum class is a friendlier way of doing this.
enum Status {
SUCCESS("Success"),
BAD_PATH("The directory does not contain the required file"),
HAS_THE_LETTER_C("The directory must not contain the letter C");
private final String message;
private Status(String _message) {
message = _message;
};
#Override
public String toString() {
return message;
}
}
Status status = checkValid(something);
if (status != Status.SUCCESS) {
// Inform user of specific failure reason
}

Apache commons has a Pair class, so you could use a Pair<Boolean, String>. Alternatively, you could just return a String with the validation failure, and treat a null as non-error (i.e., the validation either returns the reason of a failure or null if there's no failure).

Java Jersey REST Request Parameter Sanitation

I'm trying to make sure my Jersey request parameters are sanitized.
When processing a Jersey GET request, do I need to filter non String types?
For example, if the parameter submitted is an integer are both option 1 (getIntData) and option 2 (getStringData) hacker safe? What about a JSON PUT request, is my ESAPI implementation enough, or do I need to validate each data parameter after it is mapped? Could it be validated before it is mapped?
Jersey Rest Example Class:
public class RestExample {
//Option 1 Submit data as an Integer
//Jersey throws an internal server error if the type is not Integer
//Is that a valid way to validate the data?
//Integer Data, not filtered
#Path("/data/int/{data}/")
#GET
#Produces(MediaType.TEXT_HTML)
public Response getIntData(#PathParam("data") Integer data){
return Response.ok("You entered:" + data).build();
}
//Option 2 Submit data as a String, then validate it and cast it to an Integer
//String Data, filtered
#Path("/data/string/{data}/")
#GET
#Produces(MediaType.TEXT_HTML)
public Response getStringData(#PathParam("data") String data) {
data = ESAPI.encoder().canonicalize(data);
if (ESAPI.validator().isValidInteger("data", data, 0, 999999, false))
{
int intData = Integer.parseInt(data);
return Response.ok("You entered:" + intData).build();
}
return Response.status(404).entity("404 Not Found").build();
}
//JSON data, HTML encoded
#Path("/post/{requestid}")
#POST
#Consumes({MediaType.APPLICATION_FORM_URLENCODED, MediaType.APPLICATION_JSON})
#Produces(MediaType.TEXT_HTML)
public Response postData(String json) {
json = ESAPI.encoder().canonicalize(json);
json = ESAPI.encoder().encodeForHTML(json);
//Is there a way to iterate through each JSON KeyValue and filter here?
ObjectMapper mapper = new ObjectMapper();
DataMap dm = new DataMap();
try {
dm = mapper.readValue(json, DataMap.class);
} catch (Exception e) {
e.printStackTrace();
}
//Do we need to validate each DataMap object value and is there a dynamic way to do it?
if (ESAPI.validator().isValidInput("strData", dm.strData, "HTTPParameterValue", 25, false, true))
{
//Is Integer validation needed or will the thrown exception be good enough?
return Response.ok("You entered:" + dm.strData + " and " + dm.intData).build();
}
return Response.status(404).entity("404 Not Found").build();
}
}
Data Map Class:
public class DataMap {
public DataMap(){}
String strData;
Integer intData;
}

The short answer is yes, though by "filter" I interpret it as "validate," because no amount of "filtering" will EVER provide you with SAFE data. You can still run into integer overflows in Java, and while those may not have immediate security concerns, they could still put parts of your application in an unplanned for state, and hacking is all about perturbing the system in ways you can control.
You packed waaaaay too many questions into one "question," but here we go:
First off, the lines
json = ESAPI.encoder().canonicalize(json);
json = ESAPI.encoder().encodeForHTML(json);
Aren't doing what you think they're doing. If your JSON is coming in as a raw String right here, these two calls are going to be applying mass rules across the entire string, when you really need to handle these with more surgical precision, which you seem to at least be subconsciously aware of in the next question.
//Is there a way to iterate through each JSON KeyValue and filter
here?
Partial duplicate of this question.
While you're in the loop discussed here, you can perform any data transformations you want, but what you should really be considering is using the JSONObject class referenced in that first link. Then you'll have JSON parsed into an object where you'll have better access to JSON key/value pairs.
//Do we need to validate each DataMap object value and is there a
dynamic way to do it?
Yes, we validate everything that comes from a user. All users are assumed to be trained hackers, and smarter than you. However if you handled filtering before you do your data mapping transformation, you don't need to do it a second time. Doing it dynamically?
Something like:
JSONObject json = new JSONObject(s);
Iterator iterator = json.keys();
while( iterator.hasNext() ){
String data = iterator.next();
//filter and or business logic
}
^^That syntax is skipping typechecks but it should get you where you need to go.
/Is Integer validation needed or will the thrown exception be good
enough?
I don't see where you're throwing an exception with these lines of code:
if (ESAPI.validator().isValidInput("strData", dm.strData, "HTTPParameterValue", 25, false, true))
{
//Is Integer validation needed or will the thrown exception be good enough?
return Response.ok("You entered:" + dm.strData + " and " + dm.intData).build();
}
Firstly, in java we have autoboxing which means this:
int foo = 555555;
String bar = "";
//the code
foo + bar;
Will be cast to a string in any instance. The compiler will promote the int to an Integer and then silently call the Integer.toString() method. Also, in your Response.ok( String ); call, THIS is where you're going to want to encodeForHTML or whatever the output context may be. Encoding methods are ALWAYS For outputting data to user, whereas canonicalize you want to call when receiving data. Finally, in this segment of code we also have an error where you're assuming that you're dealing with an HTTPParameter. NOT at this point in the code. You'll validate http Parameters in instances where you're calling request.getParameter("id"): where id isn't a large blob of data like an entire JSON response or an entire XML response. At this point you should be validating for things like "SafeString"
Usually there are parsing libraries in Java that can at least get you to the level of Java objects, but on the validation side you're always going to be running through every item and punting whatever might be malicious.
As a final note, while coding, keep these principles in mind your code will be cleaner and your thought process much more focused:
user input is NEVER safe. (Yes, even if you've run it through an XSS filter.)
Use validate and canonicalize methods whenever RECEIVING data, and encode methods whenever transferring data to a different context, where context is defined as "Html field. Http attribute. Javascript input, etc...)
Instead of using the method isValidInput() I'd suggest using getValidInput() because it will call canonicalize for you, making you have to provide one less call.
Encode ANY time your data is going to be passed to another dynamic language, like SQL, groovy, Perl, or javascript.