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Multiple tomcats on host, how to redirect requests so that client only knows about one tomcat

I have deployed two tomcats on my host on different ports. one is listening on port A and one on port B. There are webapps hosted on both the tomcats.
I need to make sure that the client which calls APIS on those webapps on both tomcats doesn't need to know both the ports. The client (angularJS) should be able to call just one tomcat and internally that tomcat should be able to redirect the request for proper service to another tomcat and pass the response back to the client.
That way I will be able to handle same origin policy also as the angularjs webapp is also deployed on the tomcat where I want to send the requests and cookies can also be used with this as there will be only one server where the cookies will be coming from.
Is there any way to achieve that? Is there any configuration that I can do on the first tomcat itself to redirect some request based on the URI to the second tomcat? or any other tool that I can deploy to support that? I heard somewhere of port redirection using iptables. Can that be used here?

The client does a request to port A, and inside the java code does a http request to http://localhost:B
To do a http request just search "java http request" and chose one of hundreds of examples. One possible way from here: How do I do a HTTP GET in Java?
public static String getHTML(String urlToRead) throws Exception {
StringBuilder result = new StringBuilder();
URL url = new URL(urlToRead);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
String line;
while ((line = rd.readLine()) != null) {
result.append(line);
}
rd.close();
return result.toString();
}

Java simple code: java.net.SocketException: Unexpected end of file from server

I wrote some simple code in Java, the method should connect to the website and return the BufferedReader.
private BufferedReader getConnection(String url_a) {
URL url;
try {
System.out.println("getting connection");
url = new URL(url_a);
HttpURLConnection urlConnection = (HttpURLConnection)
url.openConnection();
urlConnection.addRequestProperty("User-Agent",
"Mozilla/5.0 (X11; U; Linux i586; en-US; rv:1.7.3) Gecko/20040924"
+ "Epiphany/1.4.4 (Ubuntu)");
inStream = new InputStreamReader(urlConnection.getInputStream());
return new BufferedReader(inStream);
} catch (Exception ex) {
Logger.getLogger(Reader.class.getName()).log(Level.SEVERE, null, ex);
}
return null;
}
When I use it on my PC, it works fine but when I put .jar file on the server I get this error:
java.net.SocketException: Unexpected end of file from server
at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:718)
at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:579)
at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:715)
at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:579)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1322)
at dataconverter.Reader.getConnection(Reader.java.260)
Problem is quite strange because the exception isn't thrown each time, sometimes everything is OK and program works fine.
Has anybody got any ideas?

"Unexpected end of file" implies that the remote server accepted and closed the connection without sending a response. It's possible that the remote system is too busy to handle the request, or that there's a network bug that randomly drops connections.
It's also possible there is a bug in the server: something in the request causes an internal error, and the server simply closes the connection instead of sending a HTTP error response like it should. Several people suggest this is caused by missing headers or invalid header values in the request.
With the information available it's impossible to say what's going wrong. If you have access to the servers in question you can use packet sniffing tools to find what exactly is sent and received, and look at logs to of the server process to see if there are any error messages.

Summary
This exception is encountered when you are expecting a response, but the socket has been abruptly closed.
Detailed Explanation
Java's HTTPClient, found here, throws a SocketException with message "Unexpected end of file from server" in a very specific circumstance.
After making a request, HTTPClient gets an InputStream tied to the socket associated with the request. It then polls that InputStream repeatedly until it either:
Finds the string "HTTP/1."
The end of the InputStream is reached before 8 characters are read
Finds a string other than "HTTP/1."
In case of number 2, HTTPClient will throw this SocketException if any of the following are true:
The HTTP method is CONNECT
The HTTP method is POST and the client is set to streaming mode
Why would this happen
This indicates that the TCP socket has been closed before the server was able to send a response. This could happen for any number of reasons, but some possibilities are:
Network connection was lost
The server decided to close the connection
Something in between the client and the server (nginx, router, etc) terminated the request
Note: When Nginx reloads its config, it forcefully closes any in-flight HTTP Keep-Alive connections (even POSTs), causing this exact error.

I do get this error when I do not set the Authentication header or I set wrong credentials.

I would suggest using wire shark to trace packets. If you are using Ubuntu, sudo-apt get wireshark. Like Joni stated the only way to figure out whats going wrong is to follow the GET requests and their associated responses.
http://www.wireshark.org/download.html

In my case it was solved just passing proxy to connection. Thanks to #Andreas Panagiotidis.
Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("<YOUR.HOST>", 80)));
HttpsURLConnection con = (HttpsURLConnection) url.openConnection(proxy);

In my case url contained wrong chars like spaces . Overall log your url and in some cases use browser.

Most likely the headers you are setting is incorrect or not acceptable.
Example:
connnection.setRequestProperty("content-type", "application/json");

I got this exception too. MY error code is below
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod(requestMethod);
connection.setRequestProperty("Content-type", "JSON");
I found "Content-type" should not be "JSON",is wrong!
I solved this exception by update this line to below
connection.setRequestProperty("Content-type", "application/json");
you can check up your "Content-type"

Response code 401 when accesing rest based web services with correct credentials

I am getting Unauthorized error when accessing restful web services. My sample program looks like this.
public static void main(String[] args){
// Use apache commons-httpclient to create the request/response
HttpClient client = new HttpClient();
Credentials defaultcreds = new UsernamePasswordCredentials("aaa", "cdefg");
client.getState().setCredentials(AuthScope.ANY, defaultcreds);
GetMethod method = new GetMethod(
"http://localhost:8080/userService/usersByID/1234");
try {
client.executeMethod(method);
InputStream in = method.getResponseBodyAsStream();
// Use dom4j to parse the response and print nicely to the output stream
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
StringBuilder out = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
out.append(line);
}
System.out.println(out.toString());
} catch (IOException e) {
e.printStackTrace();
}
}
My credentials are correct. My web services will consume Basic Http Authentication.
I have doubt at scope of authentication.
client.getState().setCredentials(AuthScope.ANY, defaultcreds);
My credentials are correct.
Can any one help to resolve this issue.
Thanks.

First check your url via browser and verify ?? as mentioned here
Fixing 401 errors - general
Each Web Server manages user authentication in its own way. A security officer (e.g. a Web Master) at the site typically decides which users are allowed to access the URL. This person then uses Web server software to set up those users and their passwords. So if you need to access the URL (or you forgot your user ID or password), only the security officer at that site can help you. Refer any security issues direct to them.
If you think that the URL Web page *should* be accessible to all and sundry on the Internet, then a 401 message indicates a deeper problem. The first thing you can do is check your URL via a Web browser. This browser should be running on a computer to which you have never previously identified yourself in any way, and you should avoid authentication (passwords etc.) that you have used previously. Ideally all this should be done over a completely different Internet connection to any you have used before (e.g. a different ISP dial-up connection). In short, you are trying to get the same behaviour a total stranger would get if they surfed the Internet to the Web page.
If this type of browser check indicates no authority problems, then it is possible that the Web server (or surrounding systems) have been configured to disallow certain patterns of HTTP traffic. In other words, HTTP communication from a well-known Web browser is allowed, but automated communication from other systems is rejected with an 401 error code. This is unusual, but may indicate a very defensive security policy around the Web server.
Manual Fix
Hit the url from the browser and record the HTTP traffic (Headers,body)
Run the Java client code and record the HTTP traffic (Headers,body)
Analyze and fix the differences

How to disable checking for WWW-Authenticate header on 401 in HttpUrlConnection on Android?

I'm working with a web service that returns 401 when my auth cookie expires, which causes HttpUrlConnection to throw this error:
java.io.IOException: No authentication challenges found
at libcore.net.http.HttpURLConnectionImpl.getAuthorizationCredentials(HttpURLConnectionImpl.java:427)
at libcore.net.http.HttpURLConnectionImpl.processAuthHeader(HttpURLConnectionImpl.java:407)
at libcore.net.http.HttpURLConnectionImpl.processResponseHeaders(HttpURLConnectionImpl.java:356)
at ...
I know this is happening because the server isn't returning a WWW-Authenticate header, but that's out of my control. It's nice that HttpUrlConnection does this checking for me, but this is the real world and we don't always get to work with servers that perfectly follow the HTTP spec. I can't move away from HttpUrlConnection because of other code dependencies, so how do I disable the check so I can actually make use of the response?

you could try and catch the error.
try{
//code that causes error
}
catch(IOException ex){
if(ex.getMessage().equals("No authentication challenges found")){
//handle error
}
}

NTLM authentication with httpclient 4.2.1

I need to do a HTTP GET to a URL that needs NTLM authentication. I can access the URL using Firefox or Chrome on a MacBook Pro. The browser asks for the username/password combo and it works. I am now trying to do the same from Groovy using HttpClient. I followed the NTLM support guide, but I always get a 401 Unauthorized back. There is also this sentence in the response:
You do not have permission to view this directory or page using the
credentials that you supplied because your Web browser is sending a
WWW-Authenticate header field that the Web server is not configured to
accept.
I tried all kinds of combinations for the servername and domain (the remote windows pc is not on a domain) in this piece of code, but I always get the same response.
httpclient.getCredentialsProvider().setCredentials(
new AuthScope("myserver", -1),
new NTCredentials("username", "password", "MYSERVER", "MYDOMAIN"));
Anybody had the same problem and managed to solve it? Note that this is an external program that uses IIS under the hood, so I don't think I can change any settings there.
EDIT:
Unlike what I have said, I managed to change the security settings in IIS to accept BASIC authentation, so I don't have the problem anymore.

EDIT:
In my experience with setting up Kerberos or NTLM (both are single sign on), you don't have to enter username/password at all when you are already logged in to your system.
I am pretty sure that when the browser asked for username/password combo, that's not an NTLM authentication at all. Most likely the server side application has a fallback scheme to HTTP Basic Digest (that why it displayed the username/password combo). With NTLM you'll never have to enter your username/password (principal/credentials) at all, as the server will recognize who you are through the negotiation mechanism between your browser, your operating system, server and Active Directory server.
If your MacBook Pro is running on OS/X, you also need to add your OS/X to the domain.
Your server also needs to be in the same domain where the client OS/X being added.
This may not be a trivial case. Some external tools/driver may be needed. This one may be a good candidate (but I haven't tried that).
NTLM needs both the client to be a member of the same domain as the server, hence both needs to be registered in the Active Directory domain. If your server is not in the domain, than that will be another set of problem.
In order to get your browser works with NTLM, you need to install plugin (ntlmauth-plugin?). But I have never try that on MacOS/X yet. Even in Windows you still need a plugin in order to run Firefox successfully with NTLM.

HttpClient did not work for me but finally the code below worked.
Reference - http://docs.oracle.com/javase/7/docs/technotes/guides/net/http-auth.html
For quick reference -
public static String getResponse(String url, String userName, String password) throws IOException {
Authenticator.setDefault(new Authenticator() {
#Override
public PasswordAuthentication getPasswordAuthentication() {
System.out.println(getRequestingScheme() + " authentication");
return new PasswordAuthentication(userName, password.toCharArray());
}
});
URL urlRequest = new URL(url);
HttpURLConnection conn = (HttpURLConnection) urlRequest.openConnection();
conn.setDoOutput(true);
conn.setDoInput(true);
conn.setRequestMethod("GET");
StringBuilder response = new StringBuilder();
InputStream stream = conn.getInputStream();
BufferedReader in = new BufferedReader(new InputStreamReader(stream));
String str = "";
while ((str = in.readLine()) != null) {
response.append(str);
}
in.close();
return response.toString();
}