Ensure default mime mappings are applied

Fixes gh-40860

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java

@@ -120,7 +120,7 @@ public class ServerProperties {
 	/**
 	 * Custom MIME mappings in addition to the default MIME mappings.
 	 */
-	private final MimeMappings mimeMappings = MimeMappings.lazyCopy(MimeMappings.DEFAULT);
+	private final MimeMappings mimeMappings = new MimeMappings();
 
 	@NestedConfigurationProperty
 	private final Http2 http2 = new Http2();

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryCustomizer.java

@@ -95,7 +95,7 @@ public class ServletWebServerFactoryCustomizer
 		map.from(() -> this.cookieSameSiteSuppliers)
 			.whenNot(CollectionUtils::isEmpty)
 			.to(factory::setCookieSameSiteSuppliers);
-		map.from(this.serverProperties::getMimeMappings).to(factory::setMimeMappings);
+		map.from(this.serverProperties::getMimeMappings).to(factory::addMimeMappings);
 		this.webListenerRegistrars.forEach((registrar) -> registrar.register(factory));
 	}
 

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/ServerPropertiesTests.java

@@ -187,13 +187,12 @@ class ServerPropertiesTests {
 
 	@Test
 	void testDefaultMimeMapping() {
-		assertThat(this.properties.getMimeMappings())
-			.containsExactly(MimeMappings.DEFAULT.getAll().toArray(new Mapping[0]));
+		assertThat(this.properties.getMimeMappings()).isEmpty();
 	}
 
 	@Test
 	void testCustomizedMimeMapping() {
-		MimeMappings expectedMappings = MimeMappings.lazyCopy(MimeMappings.DEFAULT);
+		MimeMappings expectedMappings = new MimeMappings();
 		expectedMappings.add("mjs", "text/javascript");
 		bind("server.mime-mappings.mjs", "text/javascript");
 		assertThat(this.properties.getMimeMappings())

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryCustomizerTests.java

@@ -22,6 +22,7 @@ import java.util.Map;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentCaptor;
 
 import org.springframework.boot.autoconfigure.web.ServerProperties;
 import org.springframework.boot.context.properties.bind.Bindable;
@@ -29,6 +30,7 @@ import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySource;
 import org.springframework.boot.context.properties.source.MapConfigurationPropertySource;
 import org.springframework.boot.web.server.Cookie;
+import org.springframework.boot.web.server.MimeMappings;
 import org.springframework.boot.web.server.Shutdown;
 import org.springframework.boot.web.server.Ssl;
 import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
@@ -74,10 +76,25 @@ class ServletWebServerFactoryCustomizerTests {
 	}
 
 	@Test
-	void testCustomMimeMappings() {
+	void withNoCustomMimeMappingsThenEmptyMimeMappingsIsAdded() {
 		ConfigurableServletWebServerFactory factory = mock(ConfigurableServletWebServerFactory.class);
 		this.customizer.customize(factory);
-		then(factory).should().setMimeMappings(this.properties.getMimeMappings());
+		ArgumentCaptor<MimeMappings> mimeMappingsCaptor = ArgumentCaptor.forClass(MimeMappings.class);
+		then(factory).should().addMimeMappings(mimeMappingsCaptor.capture());
+		MimeMappings mimeMappings = mimeMappingsCaptor.getValue();
+		assertThat(mimeMappings.getAll()).isEmpty();
+	}
+
+	@Test
+	void withCustomMimeMappingsThenPopulatedMimeMappingsIsAdded() {
+		this.properties.getMimeMappings().add("a", "alpha");
+		this.properties.getMimeMappings().add("b", "bravo");
+		ConfigurableServletWebServerFactory factory = mock(ConfigurableServletWebServerFactory.class);
+		this.customizer.customize(factory);
+		ArgumentCaptor<MimeMappings> mimeMappingsCaptor = ArgumentCaptor.forClass(MimeMappings.class);
+		then(factory).should().addMimeMappings(mimeMappingsCaptor.capture());
+		MimeMappings mimeMappings = mimeMappingsCaptor.getValue();
+		assertThat(mimeMappings.getAll()).hasSize(2);
 	}
 
 	@Test

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/servlet/server/AbstractServletWebServerFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -178,6 +178,11 @@ public abstract class AbstractServletWebServerFactory extends AbstractConfigurab
 		this.mimeMappings = new MimeMappings(mimeMappings);
 	}
 
+	@Override
+	public void addMimeMappings(MimeMappings mimeMappings) {
+		mimeMappings.forEach((mapping) -> this.mimeMappings.add(mapping.getExtension(), mapping.getMimeType()));
+	}
+
 	/**
 	 * Returns the document root which will be used by the web context to serve static
 	 * files.

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/servlet/server/ConfigurableServletWebServerFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -82,6 +82,13 @@ public interface ConfigurableServletWebServerFactory
 	 */
 	void setMimeMappings(MimeMappings mimeMappings);
 
+	/**
+	 * Adds mime-type mappings.
+	 * @param mimeMappings the mime type mappings to add
+	 * @since 3.3.0
+	 */
+	void addMimeMappings(MimeMappings mimeMappings);
+
 	/**
 	 * Sets the document root directory which will be used by the web context to serve
 	 * static files.

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/servlet/server/AbstractServletWebServerFactoryTests.java

@@ -34,6 +34,7 @@ import java.security.NoSuchAlgorithmException;
 import java.security.cert.CertificateException;
 import java.security.cert.X509Certificate;
 import java.time.Duration;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Date;
@@ -1010,6 +1011,23 @@ public abstract class AbstractServletWebServerFactoryTests {
 		assertThat(configuredMimeMappings).containsExactlyInAnyOrderElementsOf(expectedMimeMappings);
 	}
 
+	@Test
+	void additionalMimeMappingsCanBeConfigured() {
+		AbstractServletWebServerFactory factory = getFactory();
+		MimeMappings additionalMimeMappings = new MimeMappings();
+		additionalMimeMappings.add("a", "alpha");
+		additionalMimeMappings.add("b", "bravo");
+		factory.addMimeMappings(additionalMimeMappings);
+		this.webServer = factory.getWebServer();
+		Collection<MimeMappings.Mapping> configuredMimeMappings = getActualMimeMappings().entrySet()
+			.stream()
+			.map((entry) -> new MimeMappings.Mapping(entry.getKey(), entry.getValue()))
+			.toList();
+		List<MimeMappings.Mapping> expectedMimeMappings = new ArrayList<>(MimeMappings.DEFAULT.getAll());
+		expectedMimeMappings.addAll(additionalMimeMappings.getAll());
+		assertThat(configuredMimeMappings).containsExactlyInAnyOrderElementsOf(expectedMimeMappings);
+	}
+
 	@Test
 	void rootServletContextResource() {
 		AbstractServletWebServerFactory factory = getFactory();