accessing session variables in javascript inside j

问题:

I need to provide data for google APIs table... so I'll send it from servlet to JSP

but how can I access this data in "googles" javascript?

I'll provide sample of another JS - very simple one - just to let me learn how to make what topic says

    <script>
        function showTable()
        {
            <%
                Object obj = session.getAttribute("list");
                List<String> list = new ArrayList<String>();
                int size = 0; 

                if (obj != null) {
                    list = (ArrayList<String>) obj;
                    size = (Integer) session.getAttribute("size");
                }

                for (int i = 0 ; i < size ; i++) {
                    String value = list.get(i);

            %>
                    alert('<%= i %> = <%= value %> ');
            <%
                }

            %>                
        }
    </script>

It has to print elements of given list... but now it's just a big scriplet with alert inside of it... for to refactor it? I don't like having to much java in JSPs, because servlet is where it should be placed

EDIT: just to sum up - I would prefer "normal" JS for loop here... Generally I'd prefer to minimize java code, and maximize JS

回答1:

Convert it to JSON in doGet() of a preprocessing servlet. You can use among others Google Gson for this. Assuming that you've a List<Person>:

List<Person> persons = createItSomehow();
String personsJson = new Gson().toJson(persons);
request.setAttribute("personsJson", personsJson);
request.getRequestDispatcher("/WEB-INF/persons.jsp").forward(request, response);

(note that I made it a request attribute instead of session attribute, you're free to change it, but I believe it doesn't necessarily need to be a session attribute as it does not represent sessionwide data)

Assign it to a JS variable in JSP as follows:

<script>
    var persons = ${personsJson};
    // ...
</script>

This way it's available as a fullworthy JS object. You could feed it straight to the Google API.

Now invoke the URL of the servlet instead of the JSP. For example, when it's mapped on an URL pattern of /persons, invoke it by http://localhost:8080/contextname/persons.

回答2:

JavaScript is executed at client side, and scriptlets, EL, and JSP tags at server side. From the point of view of the server-side code, JavaScript is just generated text, just like HTML markup.

So, if you want to have a JavaScript loop which loops over a JavaScript array in the generated HTML page, you need to generate the JavaScript code which initializes the array, and the JavaScript loop.

Here's the JSP code

var theArray = [<c:forEach items="${sessionScope.list}" var="item" varStatus="loopStatus">'${item}' <c:if ${!loopStatus.last}>, </c:if></c:forEach>];
for (var i = 0; i < theArray.length; i++) {
    alert(theArray[i]);
}

This JSP code will generate the following JavaScript code, assuming the list in the session attribute contains "banana", "apple" and "orange":

var theArray = ['banana', 'apple', 'orange', ];
for (var i = 0; i < theArray.length; i++) {
    alert(theArray[i]);
}

Make sure, though, to properly escape the values of the list in order to generate valid JavaScript code. For example, if one of the values was "I'm cool", the generated JavaScript would be

var theArray = ['I'm cool', 'apple', 'orange', ];

which is not valid anymore. Use commons-lang StringEscapeUtils.escapeEcmaScript to escape the values.

回答3:

since the ArrayList is having objects of Strings you can simply use split() method on the value of the array list. Something like as below;

function showTable() {  
  <%
       Object obj = session.getAttribute("list");
       List list = null;
       if (obj != null) {
           list = (ArrayList<String>) obj;
       } else list = new ArrayList<String>();  %>
var jsList = <%=list.toString()%>

//remove [] from content
jsList = jsList.replace("[","");
jsList = jsList.replace("]","");

//split the contents var splitContent = jsList.split(","); //an array of element

for(var i=0;i<splitContent.length;++i) {
  alert(splitContent[i]);
}

}

I hope this will help you solve this.