How do I get servlet request URL information?

In the example below we extract information about the request object path information. We extract the protocol user, server and and its assigned port number. We extract our application context path, servlet path, path info and the query string information. If we combaine all the information below we’ll get someting equals to the request.getRequestURL().

package org.kodejava.example.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class ServletUrlInformation extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request,
                          HttpServletResponse response)
            throws ServletException, IOException {
        // Getting servlet request URL
        String url = request.getRequestURL().toString();

        // Getting servlet request query string.
        String queryString = request.getQueryString();

        // Getting request information without the hostname.
        String uri = request.getRequestURI();

        // Below we extract information about the request object path
        // information.
        String scheme = request.getScheme();
        String serverName = request.getServerName();
        int portNumber = request.getServerPort();
        String contextPath = request.getContextPath();
        String servletPath = request.getServletPath();
        String pathInfo = request.getPathInfo();
        String query = request.getQueryString();

        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();
        pw.print("Url: " + url + "<br/>");
        pw.print("Uri: " + uri + "<br/>");
        pw.print("Scheme: " + scheme + "<br/>");
        pw.print("Server Name: " + serverName + "<br/>");
        pw.print("Port: " + portNumber + "<br/>");
        pw.print("Context Path: " + contextPath + "<br/>");
        pw.print("Servlet Path: " + servletPath + "<br/>");
        pw.print("Path Info: " + pathInfo + "<br/>");
        pw.print("Query: " + query);
    }
}

Register the servlet in the web.xml file and define the url-pattern to urlinfo in the servlet-mapping. When you access this servlet using the following url http://localhost:8080/urlinfo?x=1&y=1, you’ll get the following output on your browser:

Url: http://localhost:8080/urlinfo
Uri: /urlinfo
Scheme: http
Server Name: localhost
Port: 8080
Context Path: 
Servlet Path: /urlinfo
Path Info: null
Query: x=1&y=1

How do I send a response status in servlet?

package org.kodejava.example.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ResponseStatus extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // All response status is defined in the HttpServletResponse class. We
        // can then use these constants value to return process status to the
        // browser.
        response.setContentType("text/html");

        // Let say this servlet only handle request for page name inputForm. So
        // when user request for other page name error page not found 404 will
        // be returned, other wise it will be 200 which mean OK.
        String page = request.getParameter("page");
        if (page != null && page.equals("inputForm")) {
            response.setStatus(HttpServletResponse.SC_OK);
        } else {
            response.sendError(HttpServletResponse.SC_NOT_FOUND, "The requested page ["
                    + page + "] not found.");
        }
    }
}

Here is a list of all available status code that are defined in the HttpServletResponse class.

STATUS CODE DESCRIPTION
SC_ACCEPTED Status code (202) indicating that a request was accepted for processing, but was not completed
SC_BAD_GATEWAY Status code (502) indicating that the HTTP server received an invalid response from a server it consulted when acting as a proxy or gateway
SC_BAD_REQUEST Status code (400) indicating the request sent by the client was syntactically incorrect
SC_CONFLICT Status code (409) indicating that the request could not be completed due to a conflict with the current state of the resource
SC_CONTINUE Status code (100) indicating the client can continue
SC_CREATED Status code (201) indicating the request succeeded and created a new resource on the server
SC_EXPECTATION_FAILED Status code (417) indicating that the server could not meet the expectation given in the Expect request header
SC_FORBIDDEN Status code (403) indicating the server understood the request but refused to fulfill it
SC_FOUND Status code (302) indicating that the resource reside temporarily under a different URI
SC_GATEWAY_TIMEOUT Status code (504) indicating that the server did not receive a timely response from the upstream server while acting as a gateway or proxy
SC_GONE Status code (410) indicating that the resource is no longer available at the server and no forwarding address is known
SC_HTTP_VERSION_NOT_SUPPORTED Status code (505) indicating that the server does not support or refuses to support the HTTP protocol version that was used in the request message
SC_INTERNAL_SERVER_ERROR Status code (500) indicating an error inside the HTTP server which prevented it from fulfilling the request
SC_LENGTH_REQUIRED Status code (411) indicating that the request cannot be handled without a defined Content-Length
SC_METHOD_NOT_ALLOWED Status code (405) indicating that the method specified in the Request-Line is not allowed for the resource identified by the Request-URI
SC_MOVED_PERMANENTLY Status code (301) indicating that the resource has permanently moved to a new location, and that future references should use a new URI with their requests
SC_MOVED_TEMPORARILY Status code (302) indicating that the resource has temporarily moved to another location, but that future references should still use the original URI to access the resource
SC_MULTIPLE_CHOICES Status code (300) indicating that the requested resource corresponds to any one of a set of representations, each with its own specific location
SC_NO_CONTENT Status code (204) indicating that the request succeeded but that there was no new information to return
SC_NON_AUTHORITATIVE_INFORMATION Status code (203) indicating that the meta information presented by the client did not originate from the server
SC_NOT_ACCEPTABLE Status code (406) indicating that the resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request
SC_NOT_FOUND Status code (404) indicating that the requested resource is not available
SC_NOT_IMPLEMENTED Status code (501) indicating the HTTP server does not support the functionality needed to fulfill the request
SC_NOT_MODIFIED Status code (304) indicating that a conditional GET operation found that the resource was available and not modified
SC_OK Status code (200) indicating the request succeeded normally
SC_PARTIAL_CONTENT Status code (206) indicating that the server has fulfilled the partial GET request for the resource
SC_PAYMENT_REQUIRED Status code (402) reserved for future use
SC_PRECONDITION_FAILED Status code (412) indicating that the precondition given in one or more of the request-header fields evaluated to false when it was tested on the server
SC_PROXY_AUTHENTICATION_REQUIRED Status code (407) indicating that the client MUST first authenticate itself with the proxy
SC_REQUEST_ENTITY_TOO_LARGE Status code (413) indicating that the server is refusing to process the request because the request entity is larger than the server is willing or able to process
SC_REQUEST_TIMEOUT Status code (408) indicating that the client did not produce a request within the time that the server was prepared to wait
SC_REQUEST_URI_TOO_LONG Status code (414) indicating that the server is refusing to service the request because the Request-URI is longer than the server is willing to interpret
SC_REQUESTED_RANGE_NOT_SATISFIABLE Status code (416) indicating that the server cannot serve the requested byte range
SC_RESET_CONTENT Status code (205) indicating that the agent SHOULD reset the document view which caused the request to be sent
SC_SEE_OTHER Status code (303) indicating that the response to the request can be found under a different URI
SC_SERVICE_UNAVAILABLE Status code (503) indicating that the HTTP server is temporarily overloaded, and unable to handle the request
SC_SWITCHING_PROTOCOLS Status code (101) indicating the server is switching protocols according to Upgrade header
SC_TEMPORARY_REDIRECT Status code (307) indicating that the requested resource resides temporarily under a different URI
SC_UNAUTHORIZED Status code (401) indicating that the request requires HTTP authentication
SC_UNSUPPORTED_MEDIA_TYPE Status code (415) indicating that the server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method
SC_USE_PROXY Status code (305) indicating that the requested resource MUST be accessed through the proxy given by the Location field

How do I read servlet init parameter?

When configuring a servlet in the web.xml file we can define some init parameters in the servlet configuration section. This init parameter can be used to define where a configuration file of our application is stored. This simple servlet below shows how to obtain these init parameters value.

package org.kodejava.example.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class InitParameterServlet extends javax.servlet.http.HttpServlet
        implements javax.servlet.Servlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        // Get application configuration path
        String configPath = getInitParameter("configPath");

        System.out.println("Configuration Path: " + configPath);
    }
}

How do I read cookie in Servlet?

package org.kodejava.example.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class ReadCookieExample extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter writer = response.getWriter();

        Cookie[] cookies = request.getCookies();
        for (int i = 0; i < cookies.length; i++) {
            writer.println("Name: " + cookies[i].getName() + "; Value: " + cookies[i].getValue());            
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

An example result of the servlet above is:

Name: JSESSIONID; Value: A1BF9D70A238CB3359946ABA8FC3212D

How do I send a cookie in Servlet?

A cookie is a piece of information sent to a browser by a Web Server. The browser then returns that information to the Web server. This is how some Web pages remember your previous visits; for example, an E-Commerce site might use a cookie to remember which items you’ve placed in your online shopping cart. Cookies can also store user preference information, log-in data, etc.

Here is an example to send a cookie in the HTTP response object to the client browser.

package org.kodejava.example.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class WriteCookieExample extends HttpServlet {

    protected void doGet(HttpServletRequest request, 
            HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");

        // Send a cookie named username to the client. There are some others
        // properties that we can set before we send the cookie, such as comments,
        // domain name, max age, path, a secure flag, etc.
        Cookie cookie = new Cookie("username", "jduke");
        response.addCookie(cookie);
    }
}

How do I read text file in Servlet?

This example show you how to read a text file in a servlet. Using the ServletContext.getResourceAsStream() method will enable you to read a file whether the web application is deployed in an exploded format or in a war file archive.

The following servlet read the configuration.properties file from the /WEB-INF directory in our web application. The configuration.properties file is just a regular text file with the following contents.

app.appname=Servlet Examples
app.version=1.0
app.copyright=2007

Here is our ReadTextFileServlet servlet class.

package org.kodejava.example.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;

public class ReadTextFileServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html");

        // We are going to read a file called configuration.properties. This
        // file is placed under the WEB-INF directory.
        String filename = "/WEB-INF/configuration.properties";

        ServletContext context = getServletContext();

        // First get the file InputStream using ServletContext.getResourceAsStream()
        // method.
        InputStream is = context.getResourceAsStream(filename);
        if (is != null) {
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader reader = new BufferedReader(isr);
            PrintWriter writer = response.getWriter();
            String text;

            // We read the file line by line and later will be displayed on the
            // browser page.
            while ((text = reader.readLine()) != null) {
                writer.println(text + "</br>");
            }
        }
    }
}

After creating the servlet class we need to register our servlet and create a servlet-mapping in the web.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app
        PUBLIC
        "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
    <display-name>Servlet Examples</display-name>
    <servlet>
        <servlet-name>ReadTextFileServlet</servlet-name>
        <servlet-class>org.kodejava.example.servlet.ReadTextFileServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ReadTextFileServlet</servlet-name>
        <url-pattern>/readTextFileServlet</url-pattern>
    </servlet-mapping>
</web-app>

To access the servlet you can type http://localhost:8080/readTextFileServlet in your browser URL textbox..

How do I share object or data between users in web application?

In a web application there are different type of scope where we can store object or data. There are a page, request, session and application scope.

To share data between users of the web application we can put shared object in application scope which can be done by calling setAttribute() method of the ServletContext. By this way data can then be accessing by other users by calling the getAttribute() method of the ServletContext.

Let’s see the example code in a simple servlet.

package org.kodejava.example.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ApplicationContextScopeAttribute extends HttpServlet {

    protected void doGet(HttpServletRequest req, HttpServletResponse res) 
            throws ServletException, IOException {

        ServletContext context = this.getServletContext();
        context.setAttribute("HELLO.WORLD", "Hello World 123");
    }
}

And here is what we code in the JSP page to access it.

<%= getServletContext().getAttribute("HELLO.WORLD") %>

How do I get my web application real path?

This code helps you to get the physical path where your web application is deployed on the server. It may be useful so you can for instance read or write file on the server. But please aware that this method will only work when your web application is deployed in an exploded way, if it was deployed in a war format the getRealPath() method just return null.

package org.kodejava.example.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class GetWebApplicationPathServlet extends HttpServlet {

    public GetWebApplicationPathServlet() {
        super();
    }

    protected void doGet(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        String path = getServletContext().getRealPath("/");
        PrintWriter writer = res.getWriter();
        writer.println("Application path: " + path);
    }
}

How do I use JNDI to get database connection or data source?

package org.kodejava.example.jndi;

import javax.naming.InitialContext;
import javax.servlet.Servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

public class JNDITestServlet extends HttpServlet implements Servlet {

    protected void doGet(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        // This implementation of doGet method show us an example to use
        // conn obtained in the getConnection() method.
        DateFormat format = new SimpleDateFormat("dd/MM/yyyy");

        res.setContentType("text/html");
        PrintWriter writer = res.getWriter();

        Connection conn = getConnection();
        if (conn != null) {
            try {
                // A query to get current date time from Oracle database
                String sql = "SELECT SYSDATE FROM DUAL";
                PreparedStatement statement = conn.prepareStatement(sql);
                ResultSet rs = statement.executeQuery();

                while (rs.next()) {
                    Date date = rs.getDate("SYSDATE");
                    writer.println("The current date is " + format.format(date));
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (!conn.isClosed()) {
                        conn.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * Get a database connection from the registered data source in the 
     * servlet container. To registered the JNDI data source you should 
     * refer to your servlet container documentation.
     *
     * @return a database connection
     */
    private Connection getConnection() {
        Connection connection = null;
        try {
            InitialContext context = new InitialContext();
            DataSource dataSource = (DataSource) context
                    .lookup("jdbc/DataSource");
            connection = dataSource.getConnection();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return connection;
    }
}

How do I check if parameter is exists in servlet request?

ServletRequest or HttpServletRequest object has a map object that maps parameter name and its value. By accessing this map we can check if a parameter was passed in servlet request. Let’s see the example below.

package org.kodejava.example.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ParameterCheck extends HttpServlet {
    protected void doGet(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        // Check if username parameter exists
        if (req.getParameterMap().containsKey("username")) {
            String username = req.getParameter("username");
        }

        // Check if password parameter exists
        if (req.getParameterMap().containsKey("password")) {
            String password = req.getParameter("password");
        }
    }
}