Retrieving JSON Object Literal from HttpServletRequest

Question

I am writing code that needs to extract an object literal posted to a servlet. I have studied the API for the HttpServletRequest object, but it is not clear to me how to get the JSON object out of the request since it is not posted from a form element on a web page.

Raceme

Your question is confusing. Please show the JavaScript code (or whatever it might be) that causes something to be POSTed to the servlet, if it isn't a form. If you're looking for some built-in J2EE method to understand JSON object literals, there is none. – Hilariahilario

Is your problem that you are trying to send a json object from the browser to the servlet, and you can't get the information on the servlet? – Pronty

See also more popular #3832180 – Archle

Answer 1

are you looking for this ?

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    StringBuilder sb = new StringBuilder();
    BufferedReader reader = request.getReader();
    try {
        String line;
        while ((line = reader.readLine()) != null) {
            sb.append(line).append('\n');
        }
    } finally {
        reader.close();
    }
    System.out.println(sb.toString());
}

Powerhouse

This method do convert json representation into a string, but I think it is probably not the best way to handle json data. – Auxesis

Answer 2

This is simple method to get request data from HttpServletRequest using Java 8 Stream API:

String requestData = request.getReader().lines().collect(Collectors.joining());

Laspisa

This deserves more attention! Simplest solution in my opinion. – Totemism

I get java.lang.IllegalStateException: STREAMED when calling getReader(). Any tips ? – Tenancy

from inside org.eclipse.jetty.server.Request – Tenancy

Answer 3

make use of the jackson JSON processor

 ObjectMapper mapper = new ObjectMapper();
  Book book = mapper.readValue(request.getInputStream(),Book.class);

Farina

This is perfect! You rock! – Dina

@Clyde D'Cruz How to use this while using HttpExchange..?? – Circumcise

Work for me well<3 – Vocable

Answer 4

The easiest way is to populate your bean would be from a Reader object, this can be done in a single call:

BufferedReader reader = request.getReader();
Gson gson = new Gson();

MyBean myBean = gson.fromJson(reader, MyBean.class);

Endoderm

Answer 5

There is another way to do it, using org.apache.commons.io.IOUtils to extract the String from the request

String jsonString = IOUtils.toString(request.getInputStream());

Then you can do whatever you want, convert it to JSON or other object with Gson, etc.

JSONObject json = new JSONObject(jsonString);
MyObject myObject = new Gson().fromJson(jsonString, MyObject.class);

Embalm

IOUtils.toString is Deprecated I used "String jsonString = new String(ByteStreams.toByteArray(request.getInputStream()))" – Riannon

@Riannon this post is from 2015 and the question from 2009, stuff gets old – Embalm

@Riannon The JavaDocs for the deprecated method offer IOUtils.toString(InputStream input, Charset charset) as replacement. This method buffers the input internally, so there is no need to use a BufferedInputStream etc. So essentially it is the same method as previous, the only difference is that it has one more parameter - Charset charset. – Kierkegaard

Answer 6

If you're trying to get data out of the request body, the code above works. But, I think you are having the same problem I was..

If the data in the body is in JSON form, and you want it as a Java object, you'll need to parse it yourself, or use a library like google-gson to handle it for you. You should look at the docs and examples at the project's website to know how to use it. It's fairly simple.

Alarmist

Answer 7

Converting the retreived data from the request object to json object is as below using google-gson

Gson gson = new Gson();
ABCClass c1 = gson.fromJson(data, ABCClass.class);

//ABC class is a class whose strcuture matches to the data variable retrieved

Bard

Did you test this? It doesn't work. java.lang.IllegalArgumentException: class 'HttpServletRequest' declares multiple JSON fields named 'logger'. – Nicolettenicoli

Answer 8

Use following dependencies

<dependency>
   <groupId>com.google.code.gson</groupId>
   <artifactId>gson</artifactId>
   <version>2.10.1</version>
</dependency>

Version can be any latest version

We can process Json input with following line of code

BufferedReader reader = request.getReader();
Gson gson = new Gson();
MyBean myBean = gson.fromJson(reader, MyBean.class);

Cordilleras