JSON Object is built incorrectly

Question

I am trying to get data from my SQL. The Data from my Servlet is put into an array list. After that I build a JSON object and pass it to my JSP file. Now my browser is receiving the Objects really weird.

Also I can only call the first 3 of them. I tried to get all from the list with a for loop but that gave me an error. Any ideas what I am doing wrong? Oh and I am also not allowed to use JQuery. :(

I receive my JSON like this:

    {"id":"1GürtelA","kategorie":"2schuheS","oberkategorie":"3HoseB"}

But it should be:

    {"id":"1", "kategorie":"Gürtel", "oberkategorie":"A"}
    {"id":"2", "kategorie":"schuhe", "oberkategorie":"S"}
    {"id":"3", "kategorie":"Hose", "oberkategorie":"B"}

Here is the Part of my Servlet:

        List<KategorieBean> kategorien = displayKat();

        HttpSession session = request.getSession();
        session.setAttribute("kategorie", kategorien);

        response.setContentType("text/plain");
        response.setCharacterEncoding("UTF-8");
        
        String resultJson = Json.createObjectBuilder()
                .add("id", (kategorien.get(0).toString()))
                .add("kategorie", (kategorien.get(1).toString()))
                .add("oberkategorie", (kategorien.get(2).toString()))     
                .build()
                .toString();
        
        PrintWriter writer = response.getWriter();
        writer.print(resultJson);
        writer.flush();

And here is toString I had to override.

    @Override
    public String toString() {
        return id + kategorie + oberK ;
       // This method is in my Bean
    }

Does this answer your question? [How to fluently build JSON in Java?](https://stackoverflow.com/questions/8876089/how-to-fluently-build-json-in-java) — Arvind Kumar Avinash, Jun 24 '20 at 12:49

Nowhere Man · Accepted Answer · 2020-06-23T17:49:18.990

2

It seems you're using javax.json API, and your expected output is not valid JSON.

It should be an array:

[{"id":"1", "kategorie":"Gürtel", "oberkategorie":"A"},
{"id":"2", "kategorie":"schuhe", "oberkategorie":"S"},
{"id":"3", "kategorie":"Hose", "oberkategorie":"B"}]

To achieve this you need to fix your JSON building code (assuming that you have proper getters in the KategorieBean class):

JsonArrayBuilder arrayBuilder = Json.createArrayBuilder();
for (KategorieBean category : kategorien) {
    JsonObjectBuilder itemBuilder = Json.createObjectBuilder();
    arrayBuilder.add(
        itemBuilder
            .add("id", category.getId())
            .add("kategorie", category.getKategorie())
            .add("oberkategorie", category.getOberK())
            .build()
    );
}
String resultJson = arrayBuilder.build().toString();

Also this code will return all items in the category list, not only the first three ones.

edited Jun 23 '20 at 17:49

answered Jun 23 '20 at 17:42

Nowhere Man

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Yeah it is workig :D Thanks a lot :) And sorry that i did not translate the variable names and stuff. – D.Doe Jun 23 '20 at 17:47
No problem. You could have used other tools/libraries to create JSON such as Jackson or Gson - they are much more convenient and do not require this boilerplate code. – Nowhere Man Jun 23 '20 at 17:56
Yes I know. But my professor does not want us to use Libraries and stuff. He says it's important that we learn the basics before we use tools without understanding the logic behind it. – D.Doe Jun 23 '20 at 18:00

JSON Object is built incorrectly

1 Answers1