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HttpClient java.net.UnknownHostException exception when the CURL command passes

I am trying to use httpclient to make make a call to Jenkins to get a list of jobs.
When I run my code, I get an UnknownHostException.
I tried to make the same request using curl and I was able to get the result. I am not sure how to interpret this.
void nwe() throws ClientProtocolException, IOException {
HttpHost target = new HttpHost("https://<JENKINS_URL>/api");
CredentialsProvider credsProvider = new BasicCredentialsProvider();
credsProvider.setCredentials(
new AuthScope(target.getHostName(), target.getPort()),
new UsernamePasswordCredentials("username", "password"));
CloseableHttpClient httpclient = HttpClients.custom().setDefaultCredentialsProvider(credsProvider).build();
HttpGet httpGet = new HttpGet("/json");
httpGet.setHeader("Content-type", "application/json");
BasicScheme basicAuth = new BasicScheme();
HttpClientContext localContext = HttpClientContext.create();
CloseableHttpResponse response1 = httpclient.execute(target, httpGet, localContext);
System.out.println(response1.getStatusLine());
}
The CURL command on the same URL gives me the expected output
Thanks,
Amar

Read the JavaDoc for HttpHost:
Parameters: hostname - the hostname (IP or DNS name)
So you should use just (omit the protocol and context):
HttpHost target = new HttpHost( "<JENKINS_URL>" );
and then HttpGet the /api/json part.
Cheers,

Why does an HttpGet works without timeouts but with timeouts causes an internal server error?

I don't know how the HttpClient works exactly but I find it quite strange that I get an internal server error if I initialise the httpclient with new DefaultHttpClient(httpParameters) but everythings works fine if I initialise it with new DefaultHttpClient(). I should additionally mention that the error does not occur on the first request. Here's a piece of my code, are there any errors?
HttpParams httpParameters = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(httpParameters, 3000);
HttpConnectionParams.setSoTimeout(httpParameters, 5000);
HttpClient httpclient = new DefaultHttpClient(httpParameters);
HttpResponse response = httpclient.execute(new HttpGet(url));
int statusCode = response.getStatusLine().getStatusCode();

Try to change
HttpClient httpclient
to
DefaultHttpClient httpclient

java- unknown host exception when using apache http client

I am trying to make a simple GET request for a website, but I am getting unknown host exception.
Given below is my code--
DefaultHttpClient client = new DefaultHttpClient();
HttpHost targetHost=null;
targetHost= new HttpHost("google.com/", 80, "http");
HttpGet httpget = new HttpGet("about-us.html");
BasicHttpContext localcontext = new BasicHttpContext();
try {
HttpResponse response = client.execute(targetHost, httpget, localcontext);

It looks like you have a simple problem here.
The URL for your 'HttpHost' object is malformed. You need to drop the '/' from "google.com/".
It should work after that. I used your code with that single modification & it worked.
DefaultHttpClient client = new DefaultHttpClient();
HttpHost targetHost = new HttpHost("google.com", 80, "http");
HttpGet httpget = new HttpGet("about-us.html");
BasicHttpContext localContext = new BasicHttpContext();
HttpResponse response = null;
try { response = client.execute(targetHost, httpget, localContext);
System.out.println(response.getStatusLine()
}
catch(Exception e){
// Enter error-handling code here.
}

How to Handle the Session in Apache HttpClient 4.1

I am using the HttpClient 4.1.1 to test my server's REST API.
I can manage to login seem to work fine but when I try to do anything else I am failing.
Most likely I have a problem setting the cookie in the next request.
Here is my code currently:
HttpGet httpGet = new HttpGet(<my server login URL>);
httpResponse = httpClient.execute(httpGet)
sessionID = httpResponse.getFirstHeader("Set-Cookie").getValue();
httpGet.addHeader("Cookie", sessionID);
httpClient.execute(httpGet);
Is there a better way to manage the session/cookies setting in the HttpClient package?

The correct way is to prepare a CookieStore which you need to set in the HttpContext which you in turn pass on every HttpClient#execute() call.
HttpClient httpClient = new DefaultHttpClient();
CookieStore cookieStore = new BasicCookieStore();
HttpContext httpContext = new BasicHttpContext();
httpContext.setAttribute(HttpClientContext.COOKIE_STORE, cookieStore);
// ...
HttpResponse response1 = httpClient.execute(method1, httpContext);
// ...
HttpResponse response2 = httpClient.execute(method2, httpContext);
// ...

Apache HttpComponents HttpClient timeout

How do I set the connection timeout in httpcomponents httpclient? I have found the documentation at: http://hc.apache.org/httpcomponents-client-ga/tutorial/html/connmgmt.html but it is not clear how these parameters are actually set.
Also, an explanation of the difference between SO_TIMEOUT and CONNECTION_TIMEOUT would be helpful.

In version 4.3 of Apache Http Client the configuration was refactored (again). The new way looks like this:
RequestConfig.Builder requestBuilder = RequestConfig.custom();
requestBuilder.setConnectTimeout(timeout);
requestBuilder.setConnectionRequestTimeout(timeout);
HttpClientBuilder builder = HttpClientBuilder.create();
builder.setDefaultRequestConfig(requestBuilder.build());
HttpClient client = builder.build();

In HttpClient 4.3 version you can use below example.. let say for 5 seconds
int timeout = 5;
RequestConfig config = RequestConfig.custom()
.setConnectTimeout(timeout * 1000)
.setConnectionRequestTimeout(timeout * 1000)
.setSocketTimeout(timeout * 1000).build();
CloseableHttpClient client =
HttpClientBuilder.create().setDefaultRequestConfig(config).build();
HttpGet request = new HttpGet("http://localhost:8080/service"); // GET Request
response = client.execute(request);

The answer from #jontro is correct, but it's always nice to have a code snippet on how to do this. There are two ways to do this:
Version 1: Set a 10 second timeout for each of these parameters:
HttpClient httpclient = new DefaultHttpClient();
// this one causes a timeout if a connection is established but there is
// no response within 10 seconds
httpclient.getParams().setParameter(CoreConnectionPNames.SO_TIMEOUT, 10 * 1000);
// this one causes a timeout if no connection is established within 10 seconds
httpclient.getParams().setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, 10 * 1000);
// now do the execute:
HttpGet httpget = new HttpGet(URL);
HttpResponse response = httpclient.execute(httpget);
Version 2: Also set a 10 second timeout for each of these parameters:
HttpParams params = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(params, 10 * 1000);
HttpConnectionParams.setSoTimeout(params, 10 * 1000);
HttpClient httpclient = new DefaultHttpClient(params);
HttpGet httpget = new HttpGet(URL);
HttpResponse response = httpclient.execute(httpget);

In section 2.5 you see an example of how to set the CONNECTION_TIMEOUT parameter.
CONNECTION_TIMEOUT is the time waiting for the initial connection and SO_TIMEOUT is the timeout that you wait for when reading a packet after the connection is established.

I set a hard timeout for the entire request to workaround the java.net.SocketInputStream.socketRead0 problem.
private static final ScheduledExecutorService SCHEDULED_EXECUTOR = Executors.newSingleThreadScheduledExecutor()
HttpGet request = new HttpGet("http://www.example.com")
final Runnable delayedTask = new Runnable() {
#Override
public void run() {
request.abort()
}
}
SCHEDULED_EXECUTOR.schedule(delayedTask, 100000, TimeUnit.MILLISECONDS)