Create a new Maven project as follows:

Edit pom.xml:

<project>

  <modelVersion>4.0.0</modelVersion>

  <groupId>com.acme.samples</groupId>

  <artifactId>hello-portlet</artifactId>

  <version>1.0</version>

  <packaging>war</packaging>

  <build>

    <finalName>hello-portlet</finalName>

  </build>



  <dependencies>

    <dependency>

      <groupId>javax.portlet</groupId>

      <artifactId>portlet-api</artifactId>

      <version>2.0</version>

      <scope>provided</scope>

    </dependency>

  </dependencies>

</project>

Edit web.xml:

<web-app>

  <display-name>hello-portlet</display-name>

</web-app>

Edit HelloPortlet.java:

package com.acme.samples;


import java.io.IOException;


import javax.portlet.GenericPortlet;

import javax.portlet.PortletRequestDispatcher;

import javax.portlet.RenderRequest;

import javax.portlet.RenderResponse;

import javax.portlet.PortletException;

import javax.portlet.ActionRequest;

import javax.portlet.ActionResponse;

import javax.portlet.PortletMode;

import javax.portlet.PortletPreferences;


public class HelloPortlet extends GenericPortlet {


  @Override

  protected void doView(RenderRequest request, RenderResponse response) throws IOException, PortletException {


    PortletRequestDispatcher dispatcher = getPortletContext().getRequestDispatcher("/jsp/view.jsp");

    dispatcher.forward(request, response);

  }


  @Override

  protected void doEdit(RenderRequest request, RenderResponse response) throws IOException, PortletException {


    PortletRequestDispatcher dispatcher = getPortletContext().getRequestDispatcher("/jsp/edit.jsp");

    dispatcher.forward(request, response);

  }


  @Override

  public void processAction(ActionRequest request, ActionResponse response) throws IOException, PortletException {


    String borderColor = request.getParameter("border_color");

    PortletPreferences preferences = request.getPreferences();

    preferences.setValue("border_color", borderColor);

    preferences.store();


    response.setPortletMode(PortletMode.VIEW);

  }

}

Edit portlet.xml to support VIEW and EDIT modes:

<portlet-app version="2.0" xmlns="http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd"

  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

  xsi:schemaLocation="http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd">

  <portlet>

    <portlet-name>Hello</portlet-name>

    <portlet-class>com.acme.samples.HelloPortlet</portlet-class>

    <supports>

      <mime-type>text/html</mime-type>

      <portlet-mode>VIEW</portlet-mode>

      <portlet-mode>EDIT</portlet-mode>

    </supports>

    <portlet-info>

      <title>Portlet preferences</title>

    </portlet-info>

  </portlet>

</portlet-app>

Edit view.jsp:

<%@ page import="javax.portlet.PortletURL" %>

<%@ page import="javax.portlet.PortletMode" %>

<%@ page import="javax.portlet.PortletPreferences" %>

<%@ taglib uri="http://java.sun.com/portlet_2_0" prefix="portlet"%>

<portlet:defineObjects/>



<%

  PortletURL editURL = renderResponse.createRenderURL();

  editURL.setPortletMode(PortletMode.EDIT);



  PortletPreferences preferences = renderRequest.getPreferences();

  String borderColor  = preferences.getValue("border_color", "transparent");

%>



<div style="border: solid 1px <%=borderColor%>">

  <a href="<%=editURL%>">Click here to switch to edit mode!</a>

</div>

Edit edit.jsp:

<%@ page import="javax.portlet.PortletURL" %>

<%@ page import="javax.portlet.PortletMode" %>

<%@ page import="javax.portlet.PortletPreferences" %>

<%@ taglib uri="http://java.sun.com/portlet_2_0" prefix="portlet"%>

<portlet:defineObjects/>



<%

  PortletURL viewURL = renderResponse.createRenderURL();

  viewURL.setPortletMode(PortletMode.VIEW);



  PortletURL actionURL = renderResponse.createActionURL();

  PortletPreferences preferences = renderRequest.getPreferences();

  String borderColor = preferences.getValue("border_color", "transparent");

%>



<div style="border: solid 1px <%=borderColor%>">

  <a href="<%=viewURL%>">Click here to switch to view mode!</a>

  <p></p>

  <form action="<%=actionURL%>" method="POST">

    <label>Select border color:</label>

    <select name="border_color">

      <option value="transparent" <%=(borderColor == "transparent" ? "selected=\"selected\"" : "")%>>None</option>

      <option value="red" <%=(borderColor == "red" ? "selected=\"selected\"" : "")%>>Red</option>

      <option value="blue" <%=(borderColor == "blue" ? "selected=\"selected\"" : "")%>>Blue</option>

    </select>

    <input type="submit" value="Save"/>

  </form>

</div>