Source Code : Context accessor

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Context accessor

import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ContextAccessor extends HttpServlet {

  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, java.io.IOException {

    //get a servlet context attribute
    ContextObject contextObj = (ContextObject) getServletContext()
        .getAttribute("com.java2s.ContextObject");

    if (contextObj != null)
      contextObj.put(request.getRemoteAddr(), "" + new java.util.Date());

    //display
    response.setContentType("text/html");
    java.io.PrintWriter out = response.getWriter();
    out
        .println("<html><head><title>Servlet Context Attribute</title></head><body>");
    if (contextObj != null) {
      out.println("<h2>Servlet Context Attribute Values</h2>");
      out.println(contextObj.getValues());
    } else {
      out.println("<h2>Servlet Context Attribute is Null</h2>");
    }
    out.println("</body></html>");

  } //end doGet

}

//ContextObject.java

class ContextObject {

  private Map map;

  public ContextObject() {

    map = Collections.synchronizedMap(new HashMap());
  }

  public void put(Object key, Object value) {

    if (key == null || value == null)
      throw new IllegalArgumentException(
          "Invalid parameters passed to ContextObject.put");

    map.put(key, value);
  }

  public Map getMap() {

    return map;

  }

  public String getValues() {

    StringBuffer buf = new StringBuffer("");
    Set set = map.keySet();

    synchronized (map) {

      Iterator i = set.iterator();
      while (i.hasNext())
        buf.append((String) i.next() + "<br>");
    }

    return buf.toString();

  }

  public String toString() {

    return getClass().getName() + "[ " + map + " ]";
  }

}

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