ETag Easy With RESTEasy

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ETag Easy With RESTEasy

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RESTEasy is a JBoss project that provides various frameworks to help you build RESTful Web Services and RESTful Java applications. It comprises of frameworks for mock, embeddable server, rest client, proxy servers, logging and so on. In this article, we will walk-through ETag implementation and show the behaviour related to ETag done by rest easy framework. Example is developed using RESTEasy 3.7 and deployed in tomcat as RESTEasy framework is portable.

This article is a continuation of previous article

RESTEasy - A guide to implement CRUD Rest API

RESTEasy Advanced Guide - Filters and Interceptors

ETag:

ETag is an identifier passed in HTTP header for web cache validation and conditional requests for GET and PUT. There are two HTTP request header parameters like If-Match and If-None-Match to accomplish the functionalities of ETag. Read wiki for more info about ETag.

If-Match header ETag value matches in GET/PUT request it will produce/update the response otherwise preconditions failed message with status code 412
If-None-Match header ETag value doesn't match in GET/PUT request, it produces/update the response otherwise it returns the 304(Not modified)

Maven Dependency:

Start a maven web application project and add the following dependencies for rest easy framework:

<properties>
    <resteasy-version>3.7<resteasy-version>
</properties> 

<dependency>
    <groupId>org.jboss.resteasy</groupId>
    <artifactId>resteasy-jaxrs</artifactId>
    <version>${resteasy-version}</version>
</dependency>
<dependency>
    <groupId>org.jboss.resteasy</groupId>
    <artifactId>resteasy-servlet-initializer</artifactId>
    <version>${resteasy-version}</version>
</dependency>

To marshall and unmarshall Java entity, jettison provider need to be include in the dependency list.

<dependency>
   <groupId>org.jboss.resteasy</groupId>
   <artifactId>resteasy-jettison-provider</artifactId>
   <version>${resteasy-version}</version>
</dependency>

Create Service:

Let's create a employee model and rest service for create and update and see how it works.

  @XmlRootElement
  public class Employee {

      private int employeeId;
      private String employeeName;
      private long mobileNumber;
      private Date lastModifiedDate;

      public Employee() {
         this.lastModifiedDate = new Date();
      }

      public Employee(int employeeId, String employeeName, Long mobileNumber) {
         this.employeeId = employeeId;
         this.employeeName = employeeName;
         this.mobileNumber = mobileNumber;
         this.lastModifiedDate = new Date();
     }

      public int getEmployeeId() {
         return employeeId;
      }

      public void setEmployeeId(int employeeId) {
          this.employeeId = employeeId;
      }

      public String getEmployeeName() {
         return employeeName;
      }

      public void setEmployeeName(String employeeName) {
          this.employeeName = employeeName;
      }

      public long getMobileNumber() {
         return mobileNumber;
      }

      public void setMobileNumber(long mobileNumber) {
         this.mobileNumber = mobileNumber;
      }

      public Date getLastModifiedDate() {
         return this.lastModifiedDate;
      }

      public void updateDate() {
         this.lastModifiedDate = new Date();
      }
}

Employee rest service to get employee by id and patch request to update the mobile number for the employee. ETag has been generated using modified date field in employee model and evaluatePreconditions will do the magic of ETag validation. Add this EmployeeService class also singletons in ApplicationMain class.

 @Path("employees")
 public class EmployeeService {
 private static Map<Integer, Employee> employees = new HashMap<Integer, Employee>();
 static {
   employees.put(1, new Employee(1, "Nagappan", 9600030004));
 }

 @GET
 @Path("/{id}")
 @Produces({MediaType.APPLICATION_JSON})
 public Response getUserById(@PathParam("id") int id, @Context Request req) {
      CacheControl cc = new CacheControl();
      cc.setMaxAge(10);
      System.out.println(employees.get(id).getLastModifiedDate());

      EntityTag etag = new EntityTag(employees.get(id).getLastModifiedDate().hashCode()+"");
      Response.ResponseBuilder resp = req.evaluatePreconditions(etag);
      if (resp != null) {
           /* response code 412 for precondition failed.. */
           return resp.cacheControl(cc).tag(etag).build();
      } else {
         System.out.println("Pre-conditon matched");
      }

      System.out.println("generating response");
      return Response.status(200).entity(employees.get(id)).cacheControl(cc).tag(etag).build();
 }

 @PATCH
 @Path("/{id}/mobilenumber/{mobilenumber}")
 @Produces({MediaType.APPLICATION_JSON})
 public Response updateUserById(@PathParam("id") int id, @PathParam("mobilenumber") String mobilenumber, @Context Request req) {
       CacheControl cc = new CacheControl();
       cc.setMaxAge(1000);
       cc.setMustRevalidate(true);
       EntityTag etag = new EntityTag(employees.get(id).getLastModifiedDate().hashCode()+"");
       Response.ResponseBuilder resp = req.evaluatePreconditions(etag);
       if (resp!=null) {
           return resp.tag(etag).build();
       }
       employees.get(id).setMobileNumber(Long.parseLong(mobilenumber));
       employees.get(id).updateDate();
       return Response.status(200).entity("mobile number updated successfully").cacheControl(cc).build();
 }
}

Register service

Rest service registered to standalone Servlet container 3.0 ServletContainerInitializer by extending jax-rs Application class. ServletContainerInitializer is a programmatic way of registering servlets and services at the startup phase of webapplication

  @ApplicationPath("/rest")
  public class ApplicationMain extends Application {
  private Set<Object> singletons = new HashSet<>();

  public ApplicationMain() {
      singletons.add(new EmployeeService());
  }

  @Override
  public Set<Object> getSingletons() {
     return singletons;
   }
 }

Now when we hit the employee get request, it responds with ETag value.

curl -i -X GET http://localhost:8080/resteasyexamples/rest/employees/1
HTTP/1.1 200 
Cache-Control: no-transform, max-age=10
ETag: "-396822946"
Content-Type: application/json
Transfer-Encoding: chunked
Date: Fri, 24 May 2019 05:38:50 GMT

{"employee":{"employeeId":1,"employeeName":"Nagappan","mobileNumber":9600030004}}

Update the employee record only if it matches the ETag value

curl --header 'If-Match: -396822946' -i -X PATCH http://localhost:8080/resteasyexamples/rest/employees/1/mobilenumber/9000050002
HTTP/1.1 200 
Content-Type: application/json
Content-Length: 34
Date: Fri, 24 May 2019 05:43:37 GMT

mobile number updated successfully

Then get the employee record to see the change has been affected. Here If-None-Match header has been used because previous update request would have changed the ETag so it should not be that value. Returned response has the change in Mobile number.

curl --header 'If-None-Match: -396822946' -i -X GET http://localhost:8080/resteasyexamples/rest/employees/1
HTTP/1.1 200 
Cache-Control: no-transform, max-age=10
ETag: "-396510836"
Content-Type: application/json
Transfer-Encoding: chunked
Date: Fri, 24 May 2019 05:44:46 GMT

{"employee":{"employeeId":1,"employeeName":"Nagappan","mobileNumber":9000050002}}

If we give the above returned tag with header tag, if none match value, for get request we will get status code 304 resource not modified.

curl --header 'If-None-Match: -396510836' -i -X GET http://localhost:8080/resteasyexamples/rest/employees/1
HTTP/1.1 304 
Cache-Control: no-transform, max-age=10
ETag: "-396510836"
Date: Fri, 24 May 2019 05:46:17 GMT

Likewise incorrect resource ETag given in if-match header, it will return precondition failed saying the resource with that ETag is not available.

curl --header 'If-Match: -396510835' -i -X GET http://localhost:8080/resteasyexamples/rest/employees/1
HTTP/1.1 412 
Cache-Control: no-transform, max-age=10
ETag: "-396510836"
Content-Length: 0
Date: Fri, 24 May 2019 05:49:48 GMT

Reference:

RESTEasy Framework - https://resteasy.github.io/index.html

Code samples - https://github.com/nagappan080810/resteasy_workbook

Nagappan Subramanian

Nagappan is a techie-geek and a full-stack senior developer having 10+ years of experience in both front-end and back-end. He has experience on front-end web technologies like HTML, CSS, JAVASCRIPT, Angular and expert in Java and related frameworks like Spring, Struts, EJB and RESTEasy framework. He hold bachelors degree in computer science and he is very passionate in learning new technologies.

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