Arraylist实施

Question

I have a class Researcher, and an ArrayList named researcherList that contains a list of researchers.
I want to get all researchers information from the database and put it in the researcherlist ArrayList that I created, and my response to client will be list of researchers. I have written the code below please try to see the code and find the bug. It is not working. It creates an exception. Here is the exception

SEVERE: A message body writer for Java type, class java.util.ArrayList, and MIME media type, application/xml, was not found
SEVERE: Mapped exception to response: 500 (Internal Server Error) javax.ws.rs.WebApplicationException

---

@GET
@Path("/researcher/all")
@Produces({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON})
public Response getAllResearchers() {

    //TODO return proper representation object

    Researcher res = new Researcher();
    List<Researcher> researcherList = new ArrayList<Researcher>();
    try {
        ResultSet resList = researcher.getAllResearcher();

        while (resList.next()) {
            res.setId(resList.getInt("id"));
            res.setResearcherName(resList.getString("name"));
            res.setAge(resList.getInt("age"));
            res.setSex(resList.getString("sex"));
            res.setCity(resList.getString("city"));
            res.setStreet(resList.getString("street"));
            res.setTelephone(resList.getString("telephone"));
            researcherList.add(res);
        }
    } catch (SQLException ex) {
        ex.printStackTrace();
    }

    return Response.ok(researcherList).build();
}

Answer 1

You are adding the same Researcher object all the time in a loop! Are you sure it is desired?

I suppose moving Researcher res = new Researcher(); after while (resList.next()) { ..... might come in handy.

Answer 2

The Response doesn't have a handler for the ArrayList type.

I would convert it to a String and return that. As a first cut, you could try:

return Response.ok(researcherList.toString()).build();

Also, you are adding the same Researcher object every time. You should create a new Researcher object every loop iteration :

List<Researcher> researcherList = new ArrayList<Researcher>();
try {
    Researcher res = new Researcher();
    researcherList.add(res);
    ...

Your eventual solution would probably involve building an HTML String from your list:

return Response.ok(convertToHtml(researcherList)).build();

...

private static String convertToHtml(String< Researcher > researcherList) {
    // some implementation
}