HttpComponents HttpClient

External

• http://hc.apache.org/httpcomponents-client-ga/
• tutorial http://hc.apache.org/httpcomponents-client-ga/tutorial/html/index.html

Internal

• Apache Foundation

Overview

Simplest GET usage pattern:

...

HttpMethod method = new GetMethod("http://localhost:8080/");

try {

    int responseCode = httpClient.executeMethod(method);

    if (responseCode != HttpStatus.SC_OK) {

        throw new Exception("HTTP invocation failed: " + method.getStatusLine());
    }

    byte[] body = method.getResponseBody();

    ...
}
finally {

    method.releaseConnection();
}

Configuring Retry Count in Presence of Network Errors

Before starting the client:

HttpClient httpClient = ...;
int retryCount = 1;
httpClient.getParams().setParameter(
    HttpMethodParams.RETRY_HANDLER, new DefaultHttpMethodRetryHandler(retryCount , false));

Setting Socket Connect Timeout

The socket connect timeout is specified in milliseconds and it is configured using "http.connection.timeout" system property (declared as org.apache.http.params.CoreConnectionPNames.CONNECTION_TIMEOUT):

HttpClient httpClient = ...;
httpClient.getParams().setIntParameter("http.connection.timeout", 5555);

Setting Socket SO_TIMEOUT

The socket SO_TIMEOUT is specified in milliseconds and it is configured using "http.socket.timeout" system property (declared as org.apache.http.params.CoreConnectionPNames.SO_TIMEOUT):

HttpClient httpClient = ...;
httpClient.getParams().setIntParameter("http.socket.timeout", 5555);

Also see

Socket SO_TIMEOUT

Apache HTTP Components Fluent Adapter

http://hc.apache.org/httpcomponents-client-ga/tutorial/html/fluent.html

Maven

<dependency>
      <groupId>org.apache.httpcomponents</groupId>
      <artifactId>httpclient</artifactId>
      <version>4.5.1</version>
</dependency>

Multithreaded Execution

http://hc.apache.org/httpcomponents-client-ga/tutorial/html/connmgmt.html#d5e405

In order to allow execution of multiple HTTP requests concurrently on multiple threads, httpclient must be equipped with a pooling connection manager such as PoolingClientConnectionManager.

Redirect Handling

http://hc.apache.org/httpcomponents-client-4.5.x/tutorial/html/fundamentals.html#d5e334

http://hc.apache.org/httpclient-3.x/redirects.html

Turn it off:

RedirectStrategy redirectStrategy = new RedirectStrategy() {
    @Override
    public boolean isRedirected(HttpRequest request, HttpResponse response, HttpContext context) throws ProtocolException {
        return false;
    }

    @Override
    public HttpUriRequest getRedirect(HttpRequest request, HttpResponse response, HttpContext context) throws ProtocolException {
        throw new RuntimeException("getRedirect() NOT YET IMPLEMENTED");
    }
};

... HttpClients.custom().setRedirectStrategy(redirectStrategy).build();

Troubleshooting

httpclient Automatically Follows Redirects

Sometimes this is not the behavior you want, for example when you try to get the OAuth token which is embedded in the redirect Location that you are supposed to parse. See Redirect Handling above.