[BAEL-11597] Move and update Etags article

* Moved etags article related code
* Fixed existing etag Ignored test
* Added etag scentsio adding etag support to a single endpoint
* Added tests for single endpoint etag scenario
* Cleaned now unused code in spring-rest-full module

spring-boot-rest/src/main/java/com/baeldung/persistence/model/Foo.java

@@ -7,6 +7,7 @@ import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.GenerationType;
 import javax.persistence.Id;
+import javax.persistence.Version;
 
 import com.thoughtworks.xstream.annotations.XStreamAlias;
 
@@ -20,6 +21,9 @@ public class Foo implements Serializable {
 
     @Column(nullable = false)
     private String name;
+    
+    @Version
+    private long version;
 
     public Foo() {
         super();
@@ -49,6 +53,14 @@ public class Foo implements Serializable {
         this.name = name;
     }
 
+    public long getVersion() {
+        return version;
+    }
+
+    public void setVersion(long version) {
+        this.version = version;
+    }
+    
     //
 
     @Override

spring-boot-rest/src/main/java/com/baeldung/spring/WebConfig.java

@@ -9,6 +9,7 @@ import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 import org.springframework.http.converter.xml.MarshallingHttpMessageConverter;
 import org.springframework.oxm.xstream.XStreamMarshaller;
+import org.springframework.web.filter.ShallowEtagHeaderFilter;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
 
 @Configuration
@@ -45,5 +46,15 @@ public class WebConfig implements WebMvcConfigurer {
 //
 //        return xmlConverter;
 //    }
+    
+    
+    // Etags
+    
+    // If we're not using Spring Boot we can make use of
+    // AbstractAnnotationConfigDispatcherServletInitializer#getServletFilters
+    @Bean
+    public ShallowEtagHeaderFilter shallowEtagHeaderFilter() {
+        return new ShallowEtagHeaderFilter();
+    }
 
 }

spring-boot-rest/src/main/java/com/baeldung/web/controller/FooController.java

@@ -9,6 +9,7 @@ import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.DeleteMapping;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
@@ -45,6 +46,18 @@ public class FooController {
     }
 
     // API
+    
+    // Note: the global filter overrides the ETag value we set here. We can still analyze its behaviour in the Integration Test.
+    @GetMapping(value = "/{id}/custom-etag")
+    public ResponseEntity<Foo> findByIdWithCustomEtag(@PathVariable("id") final Long id,
+        final HttpServletResponse response) {
+        final Foo resourceById = RestPreconditions.checkFound(service.findOne(id));
+
+        eventPublisher.publishEvent(new SingleResourceRetrievedEvent(this, response));
+        return ResponseEntity.ok()
+            .eTag(Long.toString(resourceById.getVersion()))
+            .body(resourceById);
+    }
 
     // read - one
 

spring-boot-rest/src/main/resources/WEB-INF/web.xml

@@ -0,0 +1,18 @@
+<!--  NOTE: web.xml is not used in Spring Boot. This is just for guidance, showing how an Etag Filter would be implemented using XML-based configs  -->
+
+<!-- <?xml version="1.0" encoding="UTF-8"?> -->
+<!-- <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" -->
+<!--     xsi:schemaLocation=" -->
+<!--       http://java.sun.com/xml/ns/javaee -->
+<!--       http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0" -->
+<!-- > -->
+
+<!--     <filter> -->
+<!--         <filter-name>etagFilter</filter-name> -->
+<!--         <filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class> -->
+<!--     </filter> -->
+<!--     <filter-mapping> -->
+<!--         <filter-name>etagFilter</filter-name> -->
+<!--         <url-pattern>/*</url-pattern> -->
+<!--     </filter-mapping> -->
+<!-- </web-app> -->