Extracting a Cookie from the HTTP Response
As stated earlier, a cookie is marked by the Set-Cookie header, which you place into the HTTP response. To write a Java app that extracts cookies from an HTTP response, you must detect this header, from which you will extract the name=value pairs. This can be done in at least two ways:
- The first method is to use the
getHeaderFieldKey and getHeaderField methods from the HttpURLConnection class:
-
public String getHeaderFieldKey(int n): This method returns the key (the name) for the nth header field, where n>=0.
-
public String getHeaderField(int n): This method returns the value for the nth header field, where n>=0.
Listing 1 shows the HttpURLConnection class in an application that extracts cookies from a HTTP response.
- The second method is to use a
java.util.Map object with the URLConnection.getHeaderFields method. Obviously, using java.util.Map is very convenient because it facilitates an easy way to store key=value pairs. In fact, the getHeaderFields method returns a java.util.Map object:
public Map<String,List<String>> getHeaderFields()
Listing 2 demonstrates the alternate method of extracting cookies from an HTTP response.
Extracting a Cookie from the HTTP Response
The easiest way to place a cookie in an HTTP request is to call the URLConnection.setRequestProperty method:
public void setRequestProperty(String key, String value)
This method places a new "entry" in the HTTP request header. In this case, the key argument will be Cookie and the value argument will be a string of type name=value pairs separated by ";".
Listing 3 shows you how to send a cookie to the server using the setRequestProperty method.
Remember if the above solution fails, it's better to use a socket base connection.
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