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okhttp_practices.md

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okhttp practices

1. use okhttp to send sorts of requests.

  • instantiate a OkHttpClient object which provides methods to execute a request.
  • A builder object provides various methods to construct a real Request object
    • HttpUrl.Builder for http get request.
    • MultipartBody.Builder for multipart/form request.
    • FormBody.Builder for urlencoded form post request.
    • Request.Builder a basic builder, all other type of builder object will be passed to the method of this builder to construct the final request object.
  • A Request object to save a request built by the builder and passed to the method newCall() of OkHttpClient
  httpResponse = client.newCall(this.httpRequest).execute();
  • A Response object to save the response, which provides access to headers and body.
  if(this.httpResponse.header("Content-Type")!=null && \
  this.httpResponse.header("Content-Type").startsWith("multipart/form-data"))
    this.responseBytes=this.httpResponse.body().bytes();
  else
    this.responseString=this.httpResponse.body().string();
  this.httpResponse.close(); // must be closed after the function body() is called.

A full demo codes are as follows:

  this.client=new OkHttpClient.Builder()
            .connectTimeout(2000, TimeUnit.MILLISECONDS)
            .writeTimeout(2000, TimeUnit.MILLISECONDS)
            .readTimeout(2000, TimeUnit.MILLISECONDS)
            .build();
  MultipartBody.Builder multipartBuilder=new MultipartBody.Builder().setType(MultipartBody.FORM);              
  RequestBody bodypart=RequestBody.create(okhttp3.MediaType.get(content_type.replace("Content-Type:", "")), value);    
  Headers.Builder headerBuilder=new Headers.Builder();      
  headerBuilder.add(header);
  multipartBuilder.addPart(headerBuilder.build(), bodypart);
   
  MultipartBody tempbody=multipartBuilder.build();
  this.httpRequest=requestBuilder
      .header("Content-Type", "multipart/form-data; boundary=\""+  tempbody.boundary()+"\"")
      .header("Content-Length", String.valueOf(tempbody.contentLength()))
      .url(this.baseUrl+endpoint).post(tempbody).build();
      
  httpResponse = client.newCall(this.httpRequest).execute();
  if(this.httpResponse.header("Content-Type")!=null && this.httpResponse.header("Content-Type").startsWith("multipart/form-data"))
      this.responseBytes=this.httpResponse.body().bytes();
  else
      this.responseString=this.httpResponse.body().string();
  this.httpResponse.close();

2. construct GET request with query parameters

use HttpUrl.Builder to construct the request, common methods are as follows:

 // for adding part in URL
 public Builder addPathSegment(String pathSegment)
 // for adding query parameters
 public Builder addQueryParameter(String name, @Nullable String value)

examples:

  URL baseUrl=new URL(this.baseUrl);
  String defaultPort=baseUrl.getProtocol().equals("http")?"80":"443";
  this.getUrlBuilder.scheme(baseUrl.getProtocol())
    .host(baseUrl.getHost())
    .port(baseUrl.getPort()==-1?Integer.valueOf(defaultPort):baseUrl.getPort());
  this.getUrlBuilder.addQueryParameter(queryPair[0], value);        
  this.getUrlBuilder.addPathSegment(endpoint);
  HttpUrl getUrl=this.getUrlBuilder.build();
  this.httpRequest=requestBuilder.url(getUrl).get().build();

3. construct POST request with urlencoded form data.

use FormBody.Builder object to build the form body.

  FormBody.Builder formBodyBuilder=new FormBody.Builder();
  formBodyBuilder.add(formParam[0],value);
  FormBody formbody=this.formBodyBuilder.build();
  this.httpRequest=requestBuilder.header("Content-Type", "application/x-www-form-urlencoded")
          .header("Content-Length", String.valueOf(formbody.contentLength())).url(this.baseUrl+endpoint)
          .post(formbody).build();
  httpResponse = client.newCall(this.httpRequest).execute();