Allow child contexts to configure server properties

Previously, HttpMessageConvertersAutoConfiguration registered
ServerProperties. When this happened in a parent context, any child
contexts would skip registering ServerProperties due to its presence
in the parent context. This prevents the child contexts from
configuring their own server properties.

This commit updates HttpMessageConvertersAutoConfiguration to
bind server.servlet.encoding directly instead of enabling
ServerProperties. With ServerProperties no longer enabled in a parent
context, child contexts are now able to configure their own server
properties.

Fixes gh-21789

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfiguration.java

@@ -30,12 +30,13 @@ import org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration;
 import org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration.NotReactiveWebApplicationCondition;
 import org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration;
 import org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration;
-import org.springframework.boot.autoconfigure.web.ServerProperties;
-import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.boot.context.properties.bind.Binder;
+import org.springframework.boot.web.servlet.server.Encoding;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
+import org.springframework.core.env.Environment;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
 
@@ -71,14 +72,13 @@ public class HttpMessageConvertersAutoConfiguration {
 
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(StringHttpMessageConverter.class)
-	@EnableConfigurationProperties(ServerProperties.class)
 	protected static class StringHttpMessageConverterConfiguration {
 
 		@Bean
 		@ConditionalOnMissingBean
-		public StringHttpMessageConverter stringHttpMessageConverter(ServerProperties serverProperties) {
-			StringHttpMessageConverter converter = new StringHttpMessageConverter(
-					serverProperties.getServlet().getEncoding().getCharset());
+		public StringHttpMessageConverter stringHttpMessageConverter(Environment environment) {
+			Encoding encoding = Binder.get(environment).bindOrCreate("server.servlet.encoding", Encoding.class);
+			StringHttpMessageConverter converter = new StringHttpMessageConverter(encoding.getCharset());
 			converter.setWriteAcceptCharset(false);
 			return converter;
 		}

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/http/HttpMessageConvertersAutoConfigurationTests.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.autoconfigure.http;
 
+import java.nio.charset.StandardCharsets;
+
 import javax.json.bind.Jsonb;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -28,6 +30,7 @@ import org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration;
 import org.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfiguration.MappingJackson2HttpMessageConverterConfiguration;
 import org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration;
 import org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.ServerProperties;
 import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
@@ -237,6 +240,38 @@ class HttpMessageConvertersAutoConfigurationTests {
 				.run((context) -> assertThat(context).doesNotHaveBean(HttpMessageConverters.class));
 	}
 
+	@Test
+	void whenEncodingCharsetIsNotConfiguredThenStringMessageConverterUsesUtf8() {
+		new WebApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(HttpMessageConvertersAutoConfiguration.class))
+				.run((context) -> {
+					assertThat(context).hasSingleBean(StringHttpMessageConverter.class);
+					assertThat(context.getBean(StringHttpMessageConverter.class).getDefaultCharset())
+							.isEqualTo(StandardCharsets.UTF_8);
+				});
+	}
+
+	@Test
+	void whenEncodingCharsetIsConfiguredThenStringMessageConverterUsesSpecificCharset() {
+		new WebApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(HttpMessageConvertersAutoConfiguration.class))
+				.withPropertyValues("server.servlet.encoding.charset=UTF-16").run((context) -> {
+					assertThat(context).hasSingleBean(StringHttpMessageConverter.class);
+					assertThat(context.getBean(StringHttpMessageConverter.class).getDefaultCharset())
+							.isEqualTo(StandardCharsets.UTF_16);
+				});
+	}
+
+	@Test // gh-21789
+	void whenAutoConfigurationIsActiveThenServerPropertiesConfigurationPropertiesAreNotEnabled() {
+		new WebApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(HttpMessageConvertersAutoConfiguration.class))
+				.run((context) -> {
+					assertThat(context).hasSingleBean(HttpMessageConverters.class);
+					assertThat(context).doesNotHaveBean(ServerProperties.class);
+				});
+	}
+
 	private ApplicationContextRunner allOptionsRunner() {
 		return this.contextRunner.withConfiguration(AutoConfigurations.of(GsonAutoConfiguration.class,
 				JacksonAutoConfiguration.class, JsonbAutoConfiguration.class));