RESTful call in Java

Question

I am going to make a RESTful call in Java  However  I don t know how to make the call  Do I need to use the URLConnection or others  Can anyone help me  thank you

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This is very complicated in java  which is why I would suggest using Spring s RestTemplate abstraction   String result    restTemplate getForObject       http   example com hotels  hotel  bookings  booking        String class  42    21       Reference    Spring Blog  Rest in Spring 3  RestTemplate  Spring Reference  Accessing RESTful services on the Client JavaDoc  RestTemplate

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If you just need to make a simple call to a REST service from java you use something along these line        Stolen from http   xml nig ac jp tutorial rest index html    and http   www dr-chuck com csev-blog 2007 09 calling-rest-web-services-from-java     import java io    import java net     public class Rest        public static void main String   args  throws IOException           URL url   new URL INSERT HERE YOUR URL           String query   INSERT HERE YOUR URL PARAMETERS             make connection         URLConnection urlc   url openConnection               use post mode         urlc setDoOutput true           urlc setAllowUserInteraction false              send query         PrintStream ps   new PrintStream urlc getOutputStream             ps print query           ps close               get result         BufferedReader br   new BufferedReader new InputStreamReader urlc              getInputStream              String l   null          while   l br readLine     null                System out println l                     br close

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If you are calling a RESTful service from a Service Provider  e g Facebook  Twitter   you can do it with any flavour of your choice   If you don t want to use external libraries  you can use java net HttpURLConnection or javax net ssl HttpsURLConnection  for SSL   but that is call encapsulated in a Factory type pattern in java net URLConnection  To receive the result  you will have to connection getInputStream   which returns you an InputStream  You will then have to convert your input stream to string and parse the string into it s representative object  e g  XML  JSON  etc    Alternatively  Apache HttpClient  version 4 is the latest   It s more stable and robust than java s default URLConnection and it supports most  if not all  HTTP protocol  as well as it can be set to Strict mode   Your response will still be in InputStream and you can use it as mentioned above     Documentation on HttpClient  http   hc apache org httpcomponents-client-ga tutorial html index html

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Most Easy Solution will be using Apache http client library  refer following sample code   this code uses basic security for authenticating   Add following Dependency     lt dependency gt   lt groupId gt org apache httpcomponents lt  groupId gt   lt artifactId gt httpclient lt  artifactId gt   lt version gt 4 4 lt  version gt   lt  dependency gt     CredentialsProvider credentialsProvider   new BasicCredentialsProvider    Credentials credentials   new UsernamePasswordCredentials  username    password    credentialsProvider setCredentials AuthScope ANY  credentials   HttpClient client   HttpClientBuilder create   setDefaultCredentialsProvider credentialsProvider  build    HttpPost request   new HttpPost  https   api plivo com v1 Account MAYNJ3OT Message    HttpResponse response   client execute request          Get the response     BufferedReader rd   new BufferedReader new InputStreamReader response getEntity   getContent          String line           while   line   rd readLine       null            textView   textView   line            System out println textView

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There are several RESTful APIs around  I would recommend Jersey   https   jersey java net   Client API documentation is here   https   jersey java net documentation latest index html  Update Location for the OAuth docs in the comment below is a dead link and has moved to  https   jersey java net nonav documentation latest security html d0e12334

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You can check out the CXF  You can visit the JAX-RS Article here  Calling is as simple as this  quote    BookStore store   JAXRSClientFactory create  http   bookstore com   BookStore class       1  remote GET call to http   bookstore com bookstore Books books   store getAllBooks        2  no remote call BookResource subresource   store getBookSubresource 1       3  remote GET call to http   bookstore com bookstore 1 Book b   subresource getDescription

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I see many answers  here s what we are using in 2020 WebClient  and BTW RestTemplate is going to get deprecated   can check this  RestTemplate going to be deprecated

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Indeed  this is  very complicated in Java    From  https   jersey java net documentation latest client html  Client client   ClientBuilder newClient    WebTarget target   client target  http   foo   path  bar    Invocation Builder invocationBuilder   target request MediaType TEXT PLAIN TYPE   Response response   invocationBuilder get

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Update  It   s been almost 5 years since I wrote the answer below  today I have a different perspective   99  of the time when people use the term REST  they really mean HTTP  they could care less about    resources        representations        state transfers        uniform interfaces        hypermedia     or any other constraints or aspects of the REST architecture style identified by Fielding  The abstractions provided by various REST frameworks are therefore confusing and unhelpful   So  you want to send HTTP requests using Java in 2015  You want an API that is clear  expressive  intuitive  idiomatic  simple  What to use  I no longer use Java  but for the past few years the Java HTTP client library that has seemed the most promising and interesting is OkHttp  Check it out     You can definitely interact with RESTful web services by using URLConnection or HTTPClient to code HTTP requests   However  it s generally more desirable to use a library or framework which provides a simpler and more semantic API specifically designed for this purpose  This makes the code easier to write  read  and debug  and reduces duplication of effort  These frameworks generally implement some great features which aren t necessarily present or easy to use in lower-level libraries  such as content negotiation  caching  and authentication   Some of the most mature options are Jersey  RESTEasy  and Restlet    I m most familiar with Restlet  and Jersey  let s look at how we d make a POST request with both APIs   Jersey Example  Form form   new Form    form add  x    foo    form add  y    bar     Client client   ClientBuilder newClient     WebTarget resource   client target  http   localhost 8080 someresource     Builder request   resource request    request accept MediaType APPLICATION JSON    Response response   request get     if  response getStatusInfo   getFamily      Family SUCCESSFUL        System out println  Success      response getStatus         System out println response getEntity       else       System out println  ERROR      response getStatus             System out println response getEntity         Restlet Example  Form form   new Form    form add  x    foo    form add  y    bar     ClientResource resource   new ClientResource  http   localhost 8080 someresource     Response response   resource post form getWebRepresentation      if  response getStatus   isSuccess          System out println  Success      response getStatus         System out println response getEntity   getText       else       System out println  ERROR      response getStatus         System out println response getEntity   getText         Of course  GET requests are even simpler  and you can also specify things like entity tags and Accept headers  but hopefully these examples are usefully non-trivial but not too complex   As you can see  Restlet and Jersey have similar client APIs  I believe they were developed around the same time  and therefore influenced each other   I find the Restlet API to be a little more semantic  and therefore a little clearer  but YMMV   As I said  I m most familiar with Restlet  I ve used it in many apps for years  and I m very happy with it  It s a very mature  robust  simple  effective  active  and well-supported framework  I can t speak to Jersey or RESTEasy  but my impression is that they re both also solid choices

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I want to share my personal experience  calling a REST WS with Post JSON call  import java io BufferedReader  import java io IOException  import java io InputStreamReader  import java io PrintStream  import java net URL  import java net URLConnection   public class HWS        public static void main String   args  throws IOException           URL url   new URL  quot INSERT YOUR SERVER REQUEST quot              Insert your JSON query request         String query    quot   PARAM1    VALUE   PARAM2    VALUE   PARAM3    VALUE   PARAM4    VALUE   quot             It change the apostrophe char to double quote char  to form a correct JSON string         query query replace  quot   quot    quot   quot  quot             try                make connection             URLConnection urlc   url openConnection                  It Content Type is so important to support JSON call             urlc setRequestProperty  quot Content-Type quot    quot application xml quot                Msj  quot Conectando   quot    url toString                   use post mode             urlc setDoOutput true               urlc setAllowUserInteraction false                      send query             PrintStream ps   new PrintStream urlc getOutputStream                 ps print query               Msj  quot Consulta   quot    query               ps close                       get result             BufferedReader br   new BufferedReader new InputStreamReader urlc getInputStream                  String l   null              while   l br readLine     null                    Msj l                             br close              catch  Exception e               Msj  quot Error ocurrido quot                Msj e toString                              private static void Msj String texto           System out println texto

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You can use Async Http Client  The library also supports the WebSocket Protocol  like that       String clientChannel   UriBuilder fromPath  http   localhost 8080 api  id    build id  toString         try  AsyncHttpClient asyncHttpClient   new AsyncHttpClient                  BoundRequestBuilder postRequest   asyncHttpClient preparePost clientChannel           postRequest setHeader HttpHeaders CONTENT TYPE  MediaType APPLICATION JSON           postRequest setBody message toString        returns JSON         postRequest execute   get

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