Stackoverflow question related Test https://stackoverflow.com/questions/54294843/plus-sign-not-encoded-with-resttemplate-using-string-url-but-interpreted

PlusEncoderInterceptor.java

package com.example.company.interceptors;

import java.io.IOException;
import java.net.URI;
import lombok.NonNull;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpRequest;
import org.springframework.http.client.ClientHttpRequestExecution;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.http.client.support.HttpRequestWrapper;
import org.springframework.util.StringUtils;
import org.springframework.web.util.UriComponentsBuilder;

/**
 * RestTemplate, the '+' sign is not encoded to '%2B' anymore (changes by SPR-14828).
 * <a href="https://stackoverflow.com/questions/54294843/plus-sign-not-encoded-with-resttemplate-using-string-url-but-interpreted">SO + interpreted as space</a>
 * RFC3986 doesn't list '+' as a reserved character,
 * but it is still interpreted as a ' ' (space) when received in a Spring Boot endpoint
 */
@Slf4j
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 @NonNull URI getURI() {
                URI u = super.getURI();
                String rawQuery = u.getRawQuery();
                String strictlyEscapedQuery = StringUtils
                        .replace(rawQuery, "+", "%2B");
                if (log.isDebugEnabled() && !strictlyEscapedQuery.equals(rawQuery)) {
                    log.debug("Plus intercept> {} => {}", rawQuery, strictlyEscapedQuery);
                }
                return UriComponentsBuilder.fromUri(u)
                        .replaceQuery(strictlyEscapedQuery)
                        .build(true).toUri();
            }
        }, body);
    }
}

PlusEncoderInterceptorTest.java

import static org.junit.jupiter.api.Assertions.*;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

import java.net.URI;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.ArgumentCaptor;
import org.springframework.http.HttpRequest;
import org.springframework.http.client.ClientHttpRequestExecution;
import org.springframework.http.client.ClientHttpResponse;

class PlusEncoderInterceptorTest {
    private PlusEncoderInterceptor interceptor;
    private HttpRequest request;
    private ClientHttpRequestExecution execution;
    @BeforeEach
    public void setUp() {
        interceptor = new PlusEncoderInterceptor();
        request = mock(HttpRequest.class);
        execution = mock(ClientHttpRequestExecution.class);
    }

    @Test
    void testPlusCharacterEncoding() throws Exception {
        String originalQuery = "param1=value1+value2";
        URI originalUri = URI.create("http://example.com/api?" + originalQuery);
        when(request.getURI()).thenReturn(originalUri);

        ClientHttpResponse response = mock(ClientHttpResponse.class);
        when(execution.execute(any(), any())).thenReturn(response);

        // WHEN
        interceptor.intercept(request, new byte[0], execution);

        ArgumentCaptor<HttpRequest> requestCaptor = ArgumentCaptor.forClass(HttpRequest.class);
        verify(execution).execute(requestCaptor.capture(), any());

        URI capturedUri = requestCaptor.getValue().getURI();
        String capturedQuery = capturedUri.getRawQuery();

        // check '+' has been replaced by '%2B'
        assertEquals("param1=value1%2Bvalue2", capturedQuery);
    }
}