[maven] error: package javax.servlet does not exist

I was trying to implement a login filter in my web app with jsf 2, following this guide:

https://stackoverflow.com/tags/servlet-filters/info

after I compiled my filter and added the .class in "web-inf/classes" (as the guide says) the filter worked, but i put the wrong url to redirect to the login page so i deleted the filter.class from the folder (web-inf/classes) and tried to compile the project again , but it failed, and since then im getting "package javax.servlet does not exist"

it is weird because before it was working and i have javax.servlet in my pom.xml.. i tried cleaning the project, but nothing.

this is my filter class:

package Bean;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Created with IntelliJ IDEA.
 * User: rodrigo
 * Date: 28-04-13
 * Time: 06:54 AM
 * To change this template use File | Settings | File Templates.
 */
@WebFilter("/Contenido/*")
public class filtro implements Filter {

    @Override
    public void init(FilterConfig config) throws ServletException {
        // If you have any <init-param> in web.xml, then you could get them
        // here by config.getInitParameter("name") and assign it as field.
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws ServletException, IOException {
        HttpServletRequest req = (HttpServletRequest) request;
        LoginBean user = (LoginBean) req.getSession().getAttribute("user");

        if (user != null && user.isLoggedIn()) {
            // User is logged in, so just continue request.
            chain.doFilter(request, response);
        } else {
            // User is not logged in, so redirect to index.
            HttpServletResponse res = (HttpServletResponse) response;
            res.sendRedirect(req.getContextPath() + "/Contenido/Login.xhtml");
        }
    }

    @Override
    public void destroy() {
        // If you have assigned any expensive resources as field of
        // this Filter class, then you could clean/close them here.
    }
}

this is the error:

\Users\rodrigo\IdeaProjects\Frutemu\src\main\java\Bean\filtro.java:[5,20] error: package javax.servlet does not exist
[ERROR] \Users\rodrigo\IdeaProjects\Frutemu\src\main\java\Bean\filtro.java:[6,20] error: package javax.servlet does not exist
[ERROR] \Users\rodrigo\IdeaProjects\Frutemu\src\main\java\Bean\filtro.java:[7,20] error: package javax.servlet does not exist
[ERROR] \Users\rodrigo\IdeaProjects\Frutemu\src\main\java\Bean\filtro.java:[8,20] error: package javax.servlet does not exist
[ERROR] \Users\rodrigo\IdeaProjects\Frutemu\src\main\java\Bean\filtro.java:[9,20] error: package javax.servlet does not exist
[ERROR] \Users\rodrigo\IdeaProjects\Frutemu\src\main\java\Bean\filtro.java:[10,20] error: package javax.servlet does not exist
[ERROR] \Users\rodrigo\IdeaProjects\Frutemu\src\main\java\Bean\filtro.java:[11,31] error: package javax.servlet.annotation does not exist

my pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>Frutemu</groupId>
    <artifactId>Frutemu</artifactId>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>Frutemu Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <repositories>
        <repository>
            <id>prime-repo</id>
            <name>Prime Repo</name>
            <url>http://repository.primefaces.org</url>
        </repository>
    </repositories>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>javax.ejb</groupId>
            <artifactId>ejb-api</artifactId>
            <version>3.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.primefaces</groupId>
            <artifactId>primefaces</artifactId>
            <version>3.5</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>all-themes</artifactId>
            <version>1.0.9</version>
        </dependency>
        <dependency>
            <groupId>javax.faces</groupId>
            <artifactId>jsf-api</artifactId>
            <version>2.0</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>com.sun.faces</groupId>
            <artifactId>jsf-impl</artifactId>
            <version>2.0.2-b10</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <!-- MySQL database driver -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.21</version>
        </dependency>
        <dependency>
            <groupId>org.glassfish.web</groupId>
            <artifactId>el-impl</artifactId>
            <version>2.2.1-b04</version>
            <scope>provided</scope>
        </dependency>
        <!-- OpenJPA framework -->
        <dependency>
            <groupId>org.apache.openjpa</groupId>
            <artifactId>openjpa-all</artifactId>
            <version>2.2.0</version>
        </dependency>
        <dependency>
            <groupId>com.microsoft.sqlserver</groupId>
            <artifactId>sqljdbc4</artifactId>
            <version>4.0</version>
        </dependency>
        <dependency>
            <groupId>net.sf.jasperreports</groupId>
            <artifactId>jasperreports</artifactId>
            <version>4.1.2</version>
        </dependency>
    </dependencies>
    <build>
        <finalName>Frutemu</finalName>
        <plugins>
            <!-- Open Jpa -->
            <plugin>
                <groupId>org.apache.openjpa</groupId>
                <artifactId>openjpa-maven-plugin</artifactId>
                <version>2.2.0</version>
                <configuration>
                    <includes>**/model/*.class</includes>
                    <addDefaultConstructor>true</addDefaultConstructor>
                    <enforcePropertyRestrictions>true</enforcePropertyRestrictions>
                </configuration>
                <executions>
                    <execution>
                        <id>enhancer</id>
                        <phase>process-classes</phase>
                        <goals>
                            <goal>enhance</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <!-- Plugin para levantar una instancia de Tomcat 7 liviana, única para este proyecto -->
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.0</version>
                <configuration>
                    <url>http://127.0.0.1:8080/manager/text</url>
                    <server>TomcatServer</server>
                    <path>/Frutemu</path>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>jasperreports-maven-plugin</artifactId>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile-reports</goal>
                        </goals>
                    </execution>
                </executions>
                <dependencies>
                    <!--note this must be repeated here to pick up correct xml validation -->
                    <dependency>
                        <groupId>net.sf.jasperreports</groupId>
                        <artifactId>jasperreports</artifactId>
                        <version>4.1.2</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>
</project>

In my case, migrating a Spring 3.1 app up to 3.2.7, my solution was similar to Matthias's but a bit different -- thus why I'm documenting it here:

In my POM I found this dependency and changed it from 6.0 to 7.0:

    <dependency>
        <groupId>javax</groupId>
        <artifactId>javaee-web-api</artifactId>
        <version>7.0</version>
        <scope>provided</scope>
    </dependency>

Then later in the POM I upgraded this plugin from 6.0 to 7.0:

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-dependency-plugin</artifactId>
            <version>2.1</version>
            <executions>
                <execution>
                    ...
                    <configuration>
                        ...
                        <artifactItems>
                            <artifactItem>
                                <groupId>javax</groupId>
                                <artifactId>javaee-endorsed-api</artifactId>
                                <version>7.0</version>
                                <type>jar</type>
                            </artifactItem>
                        </artifactItems>
                    </configuration>
                </execution>
            </executions>
        </plugin>

The answer provided by @Matthias Herlitzius is mostly correct. Just for further clarity.

The servlet-api jar is best left up to the server to manage see here for detail

With that said, the dependency to add may vary according to your server/container. For example in Wildfly the dependency would be

<dependency>
    <groupId>org.jboss.spec.javax.servlet</groupId>
    <artifactId>jboss-servlet-api_3.1_spec</artifactId>
    <scope>provided</scope>
</dependency>

So becareful to check how your container has provided the servlet implementation.

I only put this code in my pom.xml and I executed the command maven install.

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.0.1</version>
    <scope>provided</scope>
</dependency>

maybe doesnt exists javaee-api-7.0.jar. download this jar and on your project right clik

1. on your project right click
2. build path
3. Configure build path
4. Add external Jars
5. javaee-api-7.0.jar choose
6. Apply and finish

I got here with a similar problem with my Gradle build and fixed it in a similar way:

Unable to load class hudson.model.User due to missing dependency javax/servlet/ServletException

fixed with:

dependencies {
   implementation('javax.servlet:javax.servlet-api:3.0.1')
}

I needed to import javaee-api as well.

  <dependency>
     <groupId>javax</groupId>
     <artifactId>javaee-api</artifactId>
     <version>7.0</version>
  </dependency>

Unless I got following error:

package javax.servlet.http does not exist
javax.servlet.annotation does not exist
javax.servlet.http does not exist
...