Forward a servlet request to another server - http

Question

Java Servlet API can forward requests to another path within the same server (identical host:port). But, forwarding to a different host:port — like proxy do — is another story.
I've tried to do that with Jersey Client, adapting the ServletRequest — method, headers, mediatype and body — to a Jersey ClientRequest (with a different base uri), making the call, and adapting back the Jersey ClientResponse — method, headers, mediatype and body — to the ServletResponse.
Adapting those manually seems wrong to me.
Isn't there a pure Servlet API solution?
Or an HTTP client capable of adapting requests back and forth when changing the host:port?

Answer 1

HTTP-Proxy-Servlet does exactly what you need.
Quick configuration
pom.xml
<dependency>
<groupId>org.mitre.dsmiley.httpproxy</groupId>
<artifactId>smiley-http-proxy-servlet</artifactId>
<version>1.7</version>
</dependency>
web.xml
<servlet>
<servlet-name>solr</servlet-name>
<servlet-class>org.mitre.dsmiley.httpproxy.ProxyServlet</servlet-class>
<init-param>
<param-name>targetUri</param-name>
<param-value>http://solrserver:8983/solr</param-value>
</init-param>
<init-param>
<param-name>log</param-name>
<param-value>true</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>solr</servlet-name>
<url-pattern>/solr/*</url-pattern>
</servlet-mapping>
Spring Integration
see also: HTTP-Proxy-Servlet Issue #15
pom.xml
<dependency>
<groupId>org.mitre.dsmiley.httpproxy</groupId>
<artifactId>smiley-http-proxy-servlet</artifactId>
<version>1.7</version>
</dependency>
ServletWrappingControllerExt.java
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.ServletWrappingController;
public class ServletWrappingControllerExt extends ServletWrappingController
{
private String pathToStrip;
public void setPathToStrip(String pathToStrip)
{
this.pathToStrip = pathToStrip;
}
#Override
protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
throws Exception
{
final HttpServletRequest wrapper = new HttpServletRequestWrapper(request)
{
#Override
public String getPathInfo()
{
//Please note that getPathInfo returns null if DispatcherServlet is configured to track url-pattern "/"
//It should be configured to track url-pattern "/*". Below is a sample DispatcherServlet configuration
/*
<servlet>
<servlet-name>spring</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>spring</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
*/
String path = super.getPathInfo();
if (path.startsWith(pathToStrip))
{
final int length = pathToStrip.length();
path = path.substring(length);
}
return path;
}
#Override
public String getServletPath()
{
return super.getServletPath();
}
};
return super.handleRequestInternal(wrapper, response);
}
}
Beans configuration
<bean id="myServletWrapper" class="ServletWrappingControllerExt">
<property name="pathToStrip" value="/solr"/>
<property name="servletClass" value="org.mitre.dsmiley.httpproxy.ProxyServlet" />
<property name="servletName" value="solr" />
<property name="initParameters">
<props>
<prop key="targetUri">http://solrserver:8983/solr</prop>
<prop key="log">true</prop>
</props>
</property>
</bean>
<bean id="myServletUrlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="urlMap">
<map>
<entry key="/solr/**" value-ref="myServletWrapper" />
</map>
</property>
<property name="order" value="1" />
</bean>

Answer 2

You should use javax.net.HttpURLConnection
Here is the psuedo code for that:
URL url = new URL("http://otherserver:otherport/url");
HttpURLConnection connection = (HttpURLConnection)url.openConnection();
// set http method if required
connection.setRequestMethod("POST");
// set request header if required
connection.setRequestProperty("header1", "value1");
// check status code
if(connection.getResponseCode() == 200) {
InputStream is = connection.getInputStream();
//transfer is to the required output stream
} else {
//write error
}

Answer 3

As far as I understand You need to send requests from Servlet and get response from other server into yours, may be you need a HTTP Client (Overview) for that.
This question might also help you.