Generating JSON with Java App Engine

1. Requirements App Engine 1.2.2. (The older version of App Engine has a problem compiling the org.json package)

2. Download Java JSON.zip from http://www.json.org

3. Read my first app engine tutorial.

4. Generate a JSON string from any java.util.List of Objects. For this instance I used the objects from #3.

public class BeerWS extends HttpServlet {

 public void process(HttpServletRequest req, HttpServletResponse resp)
   throws IOException, ServletException {
  resp.setContentType("text/plain");
     PersistenceManager persistenceManager = PMF.get()
  .getPersistenceManager();
  String query = "select from " + Beer.class.getName()
  + " order by name asc";
  List beerLocations = (List)persistenceManager.newQuery(query).execute();
  List list = new ArrayList();
  for(Beer beer : beerLocations) {
   //Add the pojo as a JSONObject
   list.add(new JSONObject(beer));
  }
  //Create a JSONArray based from the list of JSONObejcts
  JSONArray jsonArray = new JSONArray(list);
  //Then output the JSON string to the servlet response
  resp.getWriter().println(jsonArray.toString());
 }

 public void doPost(HttpServletRequest req, HttpServletResponse resp)
   throws IOException, ServletException {
  process(req, resp);
 }

 public void doGet(HttpServletRequest req, HttpServletResponse resp)
   throws IOException, ServletException {
  process(req, resp);
 }
}

5. Here's the link of the live demo. http://beer.androidph.com/beerws. Below is the object used if you have not already check my previous app engine tutorial.

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Beer {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
 private Long id;
    @Persistent
 private String name;
    @Persistent
 private Double price;
    @Persistent
 private Date lastCallTime;
    @Persistent
 private String promotions;
    @Persistent
 private String address;
    @Persistent
 private Double longitude;
    @Persistent
 private Double latitude;

    public Beer() {}
    
    public Beer(String name, Double price, 
      Date lastCallTime, String promotions, 
  String address, Double longitude, Double latitude) {
     this.name = name;
     this.price = price;
     this.lastCallTime = lastCallTime;
     this.promotions = promotions;
     this.address = address;
     this.longitude = longitude;
     this.latitude = latitude;
    }
    
    public Beer(Long id, String name, Double price, 
      Date lastCallTime, String promotions, String address, 
     Double longitude, Double latitude) {
     this.id = id;
     this.name = name;
     this.price = price;
     this.lastCallTime = lastCallTime;
     this.promotions = promotions;
     this.address = address;
     this.longitude = longitude;
     this.latitude = latitude;
    }
 public Long getId() {
  return id;
 }
 public void setId(Long id) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public Double getPrice() {
  return price;
 }
 public void setPrice(Double price) {
  this.price = price;
 }
 public Date getLastCallTime() {
  return lastCallTime;
 }
 public void setLastCallTime(Date lastCallTime) {
  this.lastCallTime = lastCallTime;
 }
 private SimpleDateFormat sdf = new SimpleDateFormat("HH:mm");
 public String getLastCallTimeString() {
  if(lastCallTime != null) {
   return sdf.format(lastCallTime);
  } else {
   return "-";
  }
 }
 public String getPromotions() {
  return promotions;
 }
 public void setPromotions(String promotions) {
  this.promotions = promotions;
 }
 public String getAddress() {
  return address;
 }
 public void setAddress(String address) {
  this.address = address;
 }
 public Double getLongitude() {
  return longitude;
 }
 public void setLongitude(Double longitude) {
  this.longitude = longitude;
 }
 public Double getLatitude() {
  return latitude;
 }
 public void setLatitude(Double latitude) {
  this.latitude = latitude;
 }
}