重定向到自定义servlet时如何从JSF添加HttpServletRequest属性？

Question

I am implementing sort of ImageServlet serving an Image, inspired by BalusC example here http://balusc.omnifaces.org/2007/04/imageservlet.html

My servlet implementation expects to have a parameter "Animal" of type Animal

 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        LOGGER.info("On ImageServlet");

        // Get Animal from request.
        Animal animal = (Animal) request.getAttribute("Animal");

My JSF page have at some point a graphicImage tag

<h:graphicImage value="faces/image?Animal=#{animalForm.animal}" />

My animalForm bean is serving the Animal correctly

public Animal getAnimal()
{
    LOGGER.info("Current animal is : " + this.animal);
    return this.animal;
}

I know that the Animal=#{animalForm.animal} is wrong as it adds a Parameter, which will be of type String and not an Attribute but I can not find the way to add a (Typed) attribute here.

I have also read about more up-to-date way of doing the same thing with omnifaces, but right now I am on an learning curve and I have (unfortunatelly) started by project with ManagedBean and Tomcat so I would need to switch to CDI objects first. I plan to do that latter once I have something working at the first place

Answer 1

There is a way to pass an(imal) object as part of query string but you will need to

• convert your animal to JSON
• and then to encode 'JSON animal' to string conforming URL Query string standard.

Bean

Convert animal to JSON string and encode to URL string:

import com.google.gson.Gson;
import java.net.URLEncoder;
//.....

Animal animal;

public Animal getAnimal() {
    return animal;
}

//...

String jsonAnimalUrlEncoded;

public String getJsonAnimalUrlEncoded() throws UnsupportedEncodingException{
    Gson gson=new Gson();
    String jsonAnimal=gson.toJson(animal);
    jsonAnimalUrlEncoded=URLEncoder.encode(jsonAnimal, "UTF-8");
    System.out.println("URL encoded JSON animal == " + jsonAnimalUrlEncoded);
    return jsonAnimalUrlEncoded;
}

JSF page (animal image)

<h:graphicImage value="faces/image?animal=#{animalForm.jsonAnimalUrlEncoded}" />

This will pass URL encoded JSON animal to your servlet as animal attribute.

Servlet side

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    LOGGER.info("On ImageServlet");

    // Get json animal url encoded string from request
    String jsonAnimalUrlEncoded = request.getAttribute("animal");
    //convert it to JSON animal
    String jsonAnimal=URLDecoder.decode(getJsonAnimalUrlEncoded(),"UTF-8");
    //transform json animal to animal java object
    Animal animal = (Animal) new Gson().fromJson(jsonAnimal, Animal.class);

    System.out.println("My name is: " + animal.getName());

    //...
}

Servlet doGet method will catch jsonAnimalUrlEncoded that you passed from JSF page, decode it back to 'normal' JSON string and convert JSON string to real animal Java object.

( it was fun writing this since Class name was Animal :) )