HTTP Header
In this chapter you will learn:
- How to get HTTP header properties from URLConnection
- How to read HTTP connnection header fields
- How to get field and get value using a for loop
HTTP header properties from URLConnection
The following code calls the methods from URLConnection to
find out the HTTP header properties.
import java.net.URL;
import java.net.URLConnection;
import java.util.Date;
//from j av a2s .c o m
public class Main {
public static void main(String args[]) throws Exception {
URL u = new URL("http://www.java2s.com");
URLConnection uc = u.openConnection();
System.out.println("Content-type: " + uc.getContentType());
System.out.println("Content-encoding: " + uc.getContentEncoding());
System.out.println("Date: " + new Date(uc.getDate()));
System.out.println("Last modified: " + new Date(uc.getLastModified()));
System.out.println("Expiration date: " + new Date(uc.getExpiration()));
System.out.println("Content-length: " + uc.getContentLength());
}
}
The code above generates the following result.
Get HTTP connnection header fields
The following code reads out the http header.
It creates a URL pointing to java2s.com frist. And then
create URLConnection from the URL. After that
it calls the getHeaderFields() method. getHeaderFields() method
returns a map. In that map the key is the HTTP header key
and the value is a List<String> which is the HTTP header value.
import java.net.URL;
import java.net.URLConnection;
import java.util.List;
import java.util.Map;
import java.util.Set;
/*from ja va 2 s . c o m*/
public class Main {
public static void main(String[] args) throws Exception {
URL url = new URL("http://www.java2s.com/");
URLConnection urlConnection = url.openConnection();
Map<String, List<String>> headers = urlConnection.getHeaderFields();
Set<Map.Entry<String, List<String>>> entrySet = headers.entrySet();
for (Map.Entry<String, List<String>> entry : entrySet) {
String headerName = entry.getKey();
System.out.println("Header Name:" + headerName);
List<String> headerValues = entry.getValue();
for (String value : headerValues) {
System.out.print("Header value:" + value);
}
System.out.println();
}
}
}
The code above generates the following result.
The following code uses Iterator to get the
HTTP header values.
import java.net.URL;
import java.net.URLConnection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/*from j a v a2s . c o m*/
public class Main {
public static void main(String[] args) throws Exception {
URL url = new URL("http://www.java2s.com/index.html");
URLConnection connection = url.openConnection();
Map responseMap = connection.getHeaderFields();
for (Iterator iterator = responseMap.keySet().iterator(); iterator.hasNext();) {
String key = (String) iterator.next();
System.out.println(key + " = ");
List values = (List) responseMap.get(key);
for (int i = 0; i < values.size(); i++) {
Object o = values.get(i);
System.out.println(o + ", ");
}
}
}
}
The code above generates the following result.
Get field and get value
The following code finds out the HTTP header by calling
getHeaderFieldKey and getHeaderField.
import java.net.URL;
import java.net.URLConnection;
//from j ava 2s .com
public class Main {
public static void main(String[] argv) throws Exception {
URL url = new URL("http://java2s.com");
URLConnection conn = url.openConnection();
for (int i = 0;; i++) {
String headerName = conn.getHeaderFieldKey(i);
String headerValue = conn.getHeaderField(i);
System.out.println(headerName);
System.out.println(headerValue);
if (headerName == null && headerValue == null) {
System.out.println("No more headers");
break;
}
}
}
}
Next chapter...
What you will learn in the next chapter:
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