Exclude Jackson XML from String encoding/decoding

Closes gh-36775

Author: rstoyanchev

spring-web/src/main/java/org/springframework/http/codec/json/JacksonJsonDecoder.java

@@ -104,9 +104,10 @@ public JacksonJsonDecoder(JsonMapper mapper, MimeType... mimeTypes) {
 		super(mapper, mimeTypes);
 	}
 
+
 	@Override
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		return super.canDecode(elementType, mimeType) && !CharSequence.class.isAssignableFrom(elementType.toClass());
+		return (super.canDecode(elementType, mimeType) && String.class != elementType.toClass());
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/http/codec/json/JacksonJsonEncoder.java

@@ -123,7 +123,7 @@ private static PrettyPrinter initSsePrettyPrinter() {
 
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		return super.canEncode(elementType, mimeType) && !String.class.isAssignableFrom(elementType.toClass());
+		return (super.canEncode(elementType, mimeType) && String.class != elementType.toClass());
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/http/codec/xml/JacksonXmlDecoder.java

@@ -102,6 +102,11 @@ public JacksonXmlDecoder(XmlMapper mapper, MimeType... mimeTypes) {
 	}
 
 
+	@Override
+	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
+		return (super.canDecode(elementType, mimeType) && String.class != elementType.toClass());
+	}
+
 	@Override
 	public Flux<Object> decode(Publisher<DataBuffer> input, ResolvableType elementType, @Nullable MimeType mimeType,
 			@Nullable Map<String, Object> hints) {

spring-web/src/main/java/org/springframework/http/codec/xml/JacksonXmlEncoder.java

@@ -97,6 +97,11 @@ public JacksonXmlEncoder(XmlMapper mapper, MimeType... mimeTypes) {
 	}
 
 
+	@Override
+	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
+		return (super.canEncode(elementType, mimeType) && String.class != elementType.toClass());
+	}
+
 	@Override
 	public Flux<DataBuffer> encode(Publisher<?> inputStream, DataBufferFactory bufferFactory, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

spring-web/src/test/java/org/springframework/http/codec/json/JacksonJsonEncoderTests.java

@@ -90,6 +90,7 @@ protected void canEncode() {
 
 		// SPR-15910
 		assertThat(this.encoder.canEncode(ResolvableType.forClass(Object.class), APPLICATION_OCTET_STREAM)).isFalse();
+		assertThat(this.encoder.canEncode(ResolvableType.forClass(String.class), null)).isFalse();
 
 		assertThatThrownBy(() -> this.encoder.canEncode(ResolvableType.forClass(MappingJacksonValue.class), APPLICATION_JSON))
 				.isInstanceOf(UnsupportedOperationException.class);

spring-web/src/test/java/org/springframework/http/codec/xml/JacksonXmlDecoderTests.java

@@ -59,7 +59,7 @@ protected void canDecode() {
 		assertThat(decoder.canDecode(ResolvableType.forClass(Pojo.class), MediaType.TEXT_XML)).isTrue();
 		assertThat(decoder.canDecode(ResolvableType.forClass(Pojo.class), new MediaType("application", "soap+xml"))).isTrue();
 		assertThat(decoder.canDecode(ResolvableType.forClass(Pojo.class), null)).isTrue();
-		assertThat(decoder.canDecode(ResolvableType.forClass(String.class), null)).isTrue();
+		assertThat(decoder.canDecode(ResolvableType.forClass(String.class), null)).isFalse();
 		assertThat(decoder.canDecode(ResolvableType.forClass(Pojo.class), MediaType.APPLICATION_JSON)).isFalse();
 	}
 

spring-web/src/test/java/org/springframework/http/codec/xml/JacksonXmlEncoderTests.java

@@ -52,7 +52,7 @@ void canEncode() {
 		assertThat(this.encoder.canEncode(pojoType, MediaType.TEXT_XML)).isTrue();
 		assertThat(this.encoder.canEncode(pojoType, new MediaType("application", "soap+xml"))).isTrue();
 		assertThat(this.encoder.canEncode(pojoType, null)).isTrue();
-		assertThat(this.encoder.canEncode(ResolvableType.forClass(String.class), null)).isTrue();
+		assertThat(this.encoder.canEncode(ResolvableType.forClass(String.class), null)).isFalse();
 		assertThat(this.encoder.canEncode(ResolvableType.NONE, null)).isTrue();
 		assertThat(this.encoder.canEncode(ResolvableType.forClass(Pojo.class), MediaType.APPLICATION_JSON)).isFalse();
 	}