Add support for form data in MockHttpServletRequestBuilder

Closes gh-32757

spring-test/src/main/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,8 +17,10 @@
 package org.springframework.test.web.servlet.request;
 
 import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.OutputStream;
 import java.net.URI;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
@@ -40,6 +42,7 @@
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpInputMessage;
 import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpOutputMessage;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.FormHttpMessageConverter;
 import org.springframework.lang.Nullable;
@@ -121,6 +124,8 @@ public class MockHttpServletRequestBuilder
 
 	private final MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<>();
 
+	private final MultiValueMap<String, String> formFields = new LinkedMultiValueMap<>();
+
 	private final List<Cookie> cookies = new ArrayList<>();
 
 	private final List<Locale> locales = new ArrayList<>();
@@ -422,6 +427,30 @@ public MockHttpServletRequestBuilder queryParams(MultiValueMap<String, String> p
 		return this;
 	}
 
+	/**
+	 * Appends the given value(s) to the given form field and also add to the
+	 * {@link #param(String, String...) request parameters} map.
+	 * @param name the field name
+	 * @param values one or more values
+	 * @since 6.1.7
+	 */
+	public MockHttpServletRequestBuilder formField(String name, String... values) {
+		param(name, values);
+		this.formFields.addAll(name, Arrays.asList(values));
+		return this;
+	}
+
+	/**
+	 * Variant of {@link #formField(String, String...)} with a {@link MultiValueMap}.
+	 * @param formFields the form fields to add
+	 * @since 6.1.7
+	 */
+	public MockHttpServletRequestBuilder formFields(MultiValueMap<String, String> formFields) {
+		params(formFields);
+		this.formFields.addAll(formFields);
+		return this;
+	}
+
 	/**
 	 * Add the given cookies to the request. Cookies are always added.
 	 * @param cookies the cookies to add
@@ -629,6 +658,12 @@ public Object merge(@Nullable Object parent) {
 				this.queryParams.put(paramName, entry.getValue());
 			}
 		}
+		for (Map.Entry<String, List<String>> entry : parentBuilder.formFields.entrySet()) {
+			String paramName = entry.getKey();
+			if (!this.formFields.containsKey(paramName)) {
+				this.formFields.put(paramName, entry.getValue());
+			}
+		}
 		for (Cookie cookie : parentBuilder.cookies) {
 			if (!containsCookie(cookie)) {
 				this.cookies.add(cookie);
@@ -744,6 +779,24 @@ public final MockHttpServletRequest buildRequest(ServletContext servletContext)
 			}
 		});
 
+		if (!this.formFields.isEmpty()) {
+			if (this.content != null && this.content.length > 0) {
+				throw new IllegalStateException("Could not write form data with an existing body");
+			}
+			Charset charset = (this.characterEncoding != null
+					? Charset.forName(this.characterEncoding) : StandardCharsets.UTF_8);
+			MediaType mediaType = (request.getContentType() != null
+					? MediaType.parseMediaType(request.getContentType())
+					: new MediaType(MediaType.APPLICATION_FORM_URLENCODED, charset));
+			if (!mediaType.isCompatibleWith(MediaType.APPLICATION_FORM_URLENCODED)) {
+				throw new IllegalStateException("Invalid content type: '" + mediaType
+						+ "' is not compatible with '" + MediaType.APPLICATION_FORM_URLENCODED + "'");
+			}
+			request.setContent(writeFormData(mediaType, charset));
+			if (request.getContentType() == null) {
+				request.setContentType(mediaType.toString());
+			}
+		}
 		if (this.content != null && this.content.length > 0) {
 			String requestContentType = request.getContentType();
 			if (requestContentType != null) {
@@ -820,6 +873,32 @@ private void addRequestParams(MockHttpServletRequest request, MultiValueMap<Stri
 		}));
 	}
 
+	private byte[] writeFormData(MediaType mediaType, Charset charset) {
+		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		HttpOutputMessage message = new HttpOutputMessage() {
+			@Override
+			public OutputStream getBody() {
+				return out;
+			}
+
+			@Override
+			public HttpHeaders getHeaders() {
+				HttpHeaders headers = new HttpHeaders();
+				headers.setContentType(mediaType);
+				return headers;
+			}
+		};
+		try {
+			FormHttpMessageConverter messageConverter = new FormHttpMessageConverter();
+			messageConverter.setCharset(charset);
+			messageConverter.write(this.formFields, mediaType, message);
+			return out.toByteArray();
+		}
+		catch (IOException ex) {
+			throw new IllegalStateException("Failed to write form data to request body", ex);
+		}
+	}
+
 	private MultiValueMap<String, String> parseFormData(MediaType mediaType) {
 		HttpInputMessage message = new HttpInputMessage() {
 			@Override

spring-test/src/test/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilderTests.java

@@ -29,6 +29,7 @@
 
 import jakarta.servlet.ServletContext;
 import jakarta.servlet.http.Cookie;
+import org.assertj.core.api.ThrowingConsumer;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.http.HttpHeaders;
@@ -47,6 +48,8 @@
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+import static org.assertj.core.api.Assertions.entry;
 import static org.springframework.http.HttpMethod.GET;
 import static org.springframework.http.HttpMethod.POST;
 
@@ -288,6 +291,70 @@ void queryParameterList() {
 		assertThat(request.getParameter("foo[1]")).isEqualTo("baz");
 	}
 
+	@Test
+	void formField() {
+		this.builder = new MockHttpServletRequestBuilder(POST, "/");
+		this.builder.formField("foo", "bar");
+		this.builder.formField("foo", "baz");
+
+		MockHttpServletRequest request = this.builder.buildRequest(this.servletContext);
+
+		assertThat(request.getParameterMap().get("foo")).containsExactly("bar", "baz");
+		assertThat(request).satisfies(hasFormData("foo=bar&foo=baz"));
+	}
+
+	@Test
+	void formFieldMap() {
+		this.builder = new MockHttpServletRequestBuilder(POST, "/");
+		MultiValueMap<String, String> formFields = new LinkedMultiValueMap<>();
+		List<String> values = new ArrayList<>();
+		values.add("bar");
+		values.add("baz");
+		formFields.put("foo", values);
+		this.builder.formFields(formFields);
+
+		MockHttpServletRequest request = this.builder.buildRequest(this.servletContext);
+
+		assertThat(request.getParameterMap().get("foo")).containsExactly("bar", "baz");
+		assertThat(request).satisfies(hasFormData("foo=bar&foo=baz"));
+	}
+
+	@Test
+	void formFieldsAreEncoded() {
+		MockHttpServletRequest request = new MockHttpServletRequestBuilder(POST, "/")
+				.formField("name 1", "value 1").formField("name 2", "value A", "value B")
+				.buildRequest(new MockServletContext());
+		assertThat(request.getParameterMap()).containsOnly(
+				entry("name 1", new String[] { "value 1" }),
+				entry("name 2", new String[] { "value A", "value B" }));
+		assertThat(request).satisfies(hasFormData("name+1=value+1&name+2=value+A&name+2=value+B"));
+	}
+
+	@Test
+	void formFieldWithContent() {
+		this.builder = new MockHttpServletRequestBuilder(POST, "/");
+		this.builder.content("Should not have content");
+		this.builder.formField("foo", "bar");
+		assertThatIllegalStateException().isThrownBy(() -> this.builder.buildRequest(this.servletContext))
+				.withMessage("Could not write form data with an existing body");
+	}
+
+	@Test
+	void formFieldWithIncompatibleMediaType() {
+		this.builder = new MockHttpServletRequestBuilder(POST, "/");
+		this.builder.contentType(MediaType.TEXT_PLAIN);
+		this.builder.formField("foo", "bar");
+		assertThatIllegalStateException().isThrownBy(() -> this.builder.buildRequest(this.servletContext))
+				.withMessage("Invalid content type: 'text/plain' is not compatible with 'application/x-www-form-urlencoded'");
+	}
+
+	private ThrowingConsumer<MockHttpServletRequest> hasFormData(String body) {
+		return request -> {
+			assertThat(request.getContentAsString()).isEqualTo(body);
+			assertThat(request.getContentType()).isEqualTo("application/x-www-form-urlencoded;charset=UTF-8");
+		};
+	}
+
 	@Test
 	void requestParameterFromQueryWithEncoding() {
 		this.builder = new MockHttpServletRequestBuilder(GET, "/?foo={value}", "bar=baz");