AirlineServlet.java

#set( $symbol_pound = '#' )
#set( $symbol_dollar = '$' )
#set( $symbol_escape = '\' )
package ${package};

import com.google.common.annotations.VisibleForTesting;

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;
import java.util.HashMap;
import java.util.Map;

/**
 * This servlet ultimately provides a REST API for working with an
 * <code>Airline</code>.  However, in its current state, it is an example
 * of how to use HTTP and Java servlets to store simple key/value pairs.
 */
public class AirlineServlet extends HttpServlet {
  private final Map<String, String> data = new HashMap<>();

  /**
   * Handles an HTTP GET request from a client by writing the value of the key
   * specified in the "key" HTTP parameter to the HTTP response.  If the "key"
   * parameter is not specified, all of the key/value pairs are written to the
   * HTTP response.
   */
  @Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/plain");

    String key = getParameter("key", request);
    if (key != null) {
      writeValue(key, response);

    } else {
      writeAllMappings(response);
    }
  }

  /**
   * Handles an HTTP POST request by storing the key/value pair specified by the
   * "key" and "value" request parameters.  It writes the key/value pair to the
   * HTTP response.
   */
  @Override
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/plain");

    String key = getParameter("key", request);
    if (key == null) {
      missingRequiredParameter(response, "key");
      return;
    }

    String value = getParameter("value", request);
    if (value == null) {
      missingRequiredParameter(response, "value");
      return;
    }

    this.data.put(key, value);

    PrintWriter pw = response.getWriter();
    pw.println(Messages.mappedKeyValue(key, value));
    pw.flush();

    response.setStatus(HttpServletResponse.SC_OK);
  }

  /**
   * Handles an HTTP DELETE request by removing all key/value pairs.  This
   * behavior is exposed for testing purposes only.  It's probably not
   * something that you'd want a real application to expose.
   */
  @Override
  protected void doDelete(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      response.setContentType("text/plain");

      this.data.clear();

      PrintWriter pw = response.getWriter();
      pw.println(Messages.allMappingsDeleted());
      pw.flush();

      response.setStatus(HttpServletResponse.SC_OK);

  }

  /**
   * Writes an error message about a missing parameter to the HTTP response.
   *
   * The text of the error message is created by {@link Messages${symbol_pound}missingRequiredParameter(String)}
   */
  private void missingRequiredParameter(HttpServletResponse response, String parameterName)
    throws IOException {
    String message = Messages.missingRequiredParameter(parameterName);
    response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED, message);
  }

  /**
   * Writes the value of the given key to the HTTP response.
   *
   * The text of the message is formatted with {@link Messages${symbol_pound}getMappingCount(int)}
   * and {@link Messages${symbol_pound}formatKeyValuePair(String, String)}
   */
  private void writeValue(String key, HttpServletResponse response) throws IOException {
    String value = this.data.get(key);

    PrintWriter pw = response.getWriter();
    pw.println(Messages.getMappingCount(value != null ? 1 : 0));
    pw.println(Messages.formatKeyValuePair(key, value));

    pw.flush();

    response.setStatus(HttpServletResponse.SC_OK);
  }

  /**
   * Writes all of the key/value pairs to the HTTP response.
   *
   * The text of the message is formatted with
   * {@link Messages${symbol_pound}formatKeyValuePair(String, String)}
   */
  private void writeAllMappings(HttpServletResponse response) throws IOException {
    PrintWriter pw = response.getWriter();
    pw.println(Messages.getMappingCount(data.size()));

    for (Map.Entry<String, String> entry : this.data.entrySet()) {
      pw.println(Messages.formatKeyValuePair(entry.getKey(), entry.getValue()));
    }

    pw.flush();

    response.setStatus(HttpServletResponse.SC_OK);
  }

  /**
   * Returns the value of the HTTP request parameter with the given name.
   *
   * @return <code>null</code> if the value of the parameter is
   *         <code>null</code> or is the empty string
   */
  private String getParameter(String name, HttpServletRequest request) {
    String value = request.getParameter(name);
    if (value == null || "".equals(value)) {
      return null;

    } else {
      return value;
    }
  }

  @VisibleForTesting
  void setValueForKey(String key, String value) {
      this.data.put(key, value);
  }

  @VisibleForTesting
  String getValueForKey(String key) {
      return this.data.get(key);
  }
}