'+' (plus sign) not encoded with RestTemplate using String url, but interpreted as ' ' (space)

Gregor Eesmaa :

We are moving from Java 8 to Java 11, and thus, from Spring Boot 1.5.6 to 2.1.2. We noticed, that when using RestTemplate, the '+' sign is not encoded to '%2B' anymore (changes by SPR-14828). This would be okay, because RFC3986 doesn't list '+' as a reserved character, but it is still interpreted as a ' ' (space) when received in a Spring Boot endpoint.

We have a search query which can take optional timestamps as query parameters. The query looks something like http://example.com/search?beforeTimestamp=2019-01-21T14:56:50%2B00:00.

We can't figure out how to send an encoded plus sign, without it being double-encoded. Query parameter 2019-01-21T14:56:50+00:00 would be interpreted as 2019-01-21T14:56:50 00:00. If we were to encode the parameter ourselves (2019-01-21T14:56:50%2B00:00), then it would be received and interpreted as 2019-01-21T14:56:50%252B00:00.

An additional constraint is, that we want to set the base url elsewhere, when setting up the restTemplate, not where the query is being executed.

Alternatively, is there a way to force '+' not to be interpreted as ' ' by the endpoint?

I have written a short example demonstrating some ways of achieving stricter encoding with their drawbacks explained as comments:

package com.example.clientandserver;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
import org.springframework.web.util.DefaultUriBuilderFactory;
import org.springframework.web.util.UriComponentsBuilder;
import org.springframework.web.util.UriUtils;

import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Map;

@SpringBootApplication
@RestController
public class ClientAndServerApp implements CommandLineRunner {

    public static void main(String[] args) {
        SpringApplication.run(ClientAndServerApp.class, args);
    }

    @Override
    public void run(String... args) {
        String beforeTimestamp = "2019-01-21T14:56:50+00:00";

        // Previously - base url and raw params (encoded automatically). 
        // This worked in the earlier version of Spring Boot
        {
            RestTemplate restTemplate = new RestTemplateBuilder()
               .rootUri("http://localhost:8080").build();
            UriComponentsBuilder b = UriComponentsBuilder.fromPath("/search");
            if (beforeTimestamp != null) {
                b.queryParam("beforeTimestamp", beforeTimestamp);
            }
            restTemplate.getForEntity(b.toUriString(), Object.class);
            // Received: 2019-01-21T14:56:50 00:00
            //       Plus sign missing here ^
        }

        // Option 1 - no base url and encoding the param ourselves.
        {
            RestTemplate restTemplate = new RestTemplate();
            UriComponentsBuilder b = UriComponentsBuilder
                .fromHttpUrl("http://localhost:8080/search");
            if (beforeTimestamp != null) {
                b.queryParam(
                    "beforeTimestamp",
                    UriUtils.encode(beforeTimestamp, StandardCharsets.UTF_8)
                );
            }
            restTemplate.getForEntity(
                b.build(true).toUri(), Object.class
            ).getBody();
            // Received: 2019-01-21T14:56:50+00:00
        }

        // Option 2 - with templated base url, query parameter is not optional.
        {
            RestTemplate restTemplate = new RestTemplateBuilder()
                .rootUri("http://localhost:8080")
                .uriTemplateHandler(new DefaultUriBuilderFactory())
                .build();
            Map<String, String> params = new HashMap<>();
            params.put("beforeTimestamp", beforeTimestamp);
            restTemplate.getForEntity(
                "/search?beforeTimestamp={beforeTimestamp}",
                Object.class,
                params);
            // Received: 2019-01-21T14:56:50+00:00
        }
    }

    @GetMapping("/search")
    public void search(@RequestParam String beforeTimestamp) {
        System.out.println("Received: " + beforeTimestamp);
    }
}

Gregor Eesmaa :

We realized the URL can be modified in an interceptor after the encoding is done. So a solution would be to use an interceptor, that encodes the plus sign in the query params.

RestTemplate restTemplate = new RestTemplateBuilder()
        .rootUri("http://localhost:8080")
        .interceptors(new PlusEncoderInterceptor())
        .build();

A shortened example:

public class PlusEncoderInterceptor implements ClientHttpRequestInterceptor {

    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
        return execution.execute(new HttpRequestWrapper(request) {
            @Override
            public URI getURI() {
                URI u = super.getURI();
                String strictlyEscapedQuery = StringUtils.replace(u.getRawQuery(), "+", "%2B");
                return UriComponentsBuilder.fromUri(u)
                        .replaceQuery(strictlyEscapedQuery)
                        .build(true).toUri();
            }
        }, body);
    }
}