The high-level REST client uses a GetIndexRequest for Indices Exists API. The index name (or indices' names) are required.

GetIndexRequest request = new GetIndexRequest();
request.indices("twitter"); 

Indices Exists API also accepts following optional arguments, through a GetIndexRequest:

request.local(false); 
request.humanReadable(true); 
request.includeDefaults(false); 
request.indicesOptions(indicesOptions); 

The asynchronous execution of an indices exists request requires both the GetIndexRequest instance and an ActionListener instance to be passed to the asynchronous method:

client.indices().existsAsync(request, RequestOptions.DEFAULT, listener); 

The asynchronous method does not block and returns immediately. Once it is completed the ActionListener is called back using the onResponse method if the execution successfully completed or using the onFailure method if it failed.

A typical listener for the Indices Exists looks like:

ActionListener<Boolean> listener = new ActionListener<Boolean>() {
    @Override
    public void onResponse(Boolean exists) {
        
    }

    @Override
    public void onFailure(Exception e) {
        
    }
};

The response is a boolean value, indicating whether the index (or indices) exist:

boolean exists = client.indices().exists(request, RequestOptions.DEFAULT);