http-client-java, skip xml property of required and constant, on de-s…

…erialization (#5369)

fix #5332

The property is required, and can have only 1 value. Therefore it is not
settable (as there is only 1 value to set), and de-serialization does
not need to set the value as well.

e2e test at Azure/autorest.java#2997

packages/http-client-java/generator/http-client-generator-core/src/main/java/com/microsoft/typespec/http/client/generator/core/template/StreamSerializationModelTemplate.java

@@ -2312,10 +2312,20 @@ private void writeFromXmlDeserialization(JavaBlock methodBlock) {
 
                     // Loop over all properties and generate their deserialization handling.
                     AtomicReference<JavaIfBlock> ifBlockReference = new AtomicReference<>(ifBlock);
-                    propertiesManager.forEachSuperXmlElement(
-                        element -> handleXmlPropertyDeserialization(element, whileBlock, ifBlockReference, true));
-                    propertiesManager.forEachXmlElement(
-                        element -> handleXmlPropertyDeserialization(element, whileBlock, ifBlockReference, false));
+                    propertiesManager.forEachSuperXmlElement(element -> {
+                        if (element.isRequired() && element.isConstant()) {
+                            return;
+                        }
+                        handleXmlPropertyDeserialization(element, whileBlock, ifBlockReference, true);
+                    });
+                    propertiesManager.forEachXmlElement(element -> {
+                        if (element.isRequired() && element.isConstant()) {
+                            // the element is element of a constant, which can only have one value
+                            // skip de-serialize
+                            return;
+                        }
+                        handleXmlPropertyDeserialization(element, whileBlock, ifBlockReference, false);
+                    });
 
                     ifBlock = ifBlockReference.get();