2017年9月15日 星期五

Principle of Jersey


1. Basci principle
REST is an architectural style which is based on web-standards and the HTTP protocol.

REST allows that resources have different representations, e.g., text, XML, JSON etc. The REST client can ask for a specific representation via the HTTP protocol (content negotiation


The PUTGETPOST and DELETE methods are typical used in REST based architectures. The following table gives an explanation of these operations.
  • GET defines a reading access of the resource without side-effects. The resource is never changed via a GET request, e.g., the request has no side effects (idempotent).
  • PUT creates a new resource. It must also be idempotent.
  • DELETE removes the resources. The operations are idempotent. They can get repeated without leading to different results.
  • POST updates an existing resource or creates a new resource.

Reference:  article




2. About jersey 

Jersey  is
2.1. JAX-RS
Java defines REST support via the Java Specification Request (JSR) 311. This specification is called JAX-RS (The Java API for RESTful Web Services). JAX-RS uses annotations to define the REST relevance of Java classes.

2.2. Jersey

The Jersey implementation provides a library to implement Restful webservices in a Java servlet container. It is the reference implementation for the JSR 311 specification.
Jersey provides a servlet implementation which scans predefined classes to identify RESTful resources. You use annotations in the class and methods to define their responsibility.

2.3 Histroy
Biggest difference between Jersey 1 and Jersey 2 in this regard is used namespace. Jersey 1 uses prefix com.sun.jersey (even for property names) which is not true for the namespace of Jersey 2 that starts with org.glassfish.jersey. Besides that Jersey 2 does NOT support properties from Jersey 1 and you need to use specific ones (from Jersey 2) to make things work. ref


3. Jersey annotation

Annotation:J2SE 5.0 中對 metadata 提出的功能是 Annotation,metadata 就是「資料的資料」(Data about data),突然看到這樣的解釋會覺得奇怪,但以表格為例,表格中呈現的就是資料,但有時候還會有額外的資料用來說明表格的作用,從這個角度來看,metadata 就不這麼的奇怪。
在 J2SE 5.0 中,Annotation 的主要目的介於原始碼與 API 文件說明之間,Annotation 對程式碼作出一些說明與解釋,Class 中可以包含這些解釋,編譯器或其它程式分析工作可以使用 Annotation 來作分析,您可以從 java.lang.Override、java.lang.Deprecated、java.lang.SuppressWarnings 這三個 J2SE 5.0 中標準的 Annotation 型態開始瞭解 Annotation 的作用。 ref

AnnotationDescription
@PATH(your_path)
Sets the path to base URL + /your_path. The base URL is based on your application name (the context root), the servlet and the URL pattern from the web.xml configuration file.
@POST
Indicates that the following method will answer to an HTTP POST request.
@GET
Indicates that the following method will answer to an HTTP GET request.
@PUT
Indicates that the following method will answer to an HTTP PUT request.
@DELETE
Indicates that the following method will answer to an HTTP DELETE request.
@Produces(MediaType.TEXT_PLAIN[, more-types])
@Produces defines which MIME type is delivered by a method annotated with @GET. In the example text ("text/plain") is produced. Other examples would be "application/xml" or "application/json".
@Consumes(type[, more-types])
@Consumes defines which MIME type is consumed by this method.
@PathParam
Used to inject values from the URL into a method parameter. This way you inject, for example, the ID of a resource into the method to get the correct object.
Reference: article.html



4. Return  code 
  • 1xx: Informational - Communicates transfer protocol-level information
  • 2xx: Success -Indicates that the client’s request was accepted successfully.
  • 3xx: Redirection - Indicates that the client must take some additional action in order to complete their request.
  • 4xx: Client Error - This category of error status codes points the finger at clients.
  • 5xx: Server Error - The server takes responsibility for these error status codes.






T. Jersey Example 

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