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How to submit another get attribute and keep previous one?

I'm building my first web app in Java. I came across this problem. When I have a get attribute like ?page=2 correctly submitted it goes missing after calling another get request. How can I keep the first one and append another one? Here are pics that help clear out my question
Before
After
Desired
Here are code snippets of my forms in .jsp page. This is used to sort the table with passing a column name:
<form action="GetUsersServlet" method="get">name
<input type="hidden" name="column" value="name">
<button class="sort" type="submit"></button>
</form>
How can I append the value to existing ?page=x attribute?

Use URLSearchParams method set on event click and set window.location.search to parsed params.
document.querySelector("button").onclick = () => {
const urlParams = new URLSearchParams(window.location.search);
urlParams.set("page", 2)
window.location.search = urlParams.toString()
}

Nested Loop Binding in Thymeleaf

I am making web app using Java/Spring/Thymeleaf and don't seem to be able to get past this problem!
So, here's my thymeleaf template code:
<form th:action="#{/holiday/create}" th:object="${holiday}" method="post">
<select name="user_scroll">
<option th:each="user : ${allUsers}" th:value="${user.id}"
th:text="${user.email}" th:field="${holiday.user_id}" />
</select>
<button type="submit">
Create
</button>
</form>
I have read the related questions on here but am still stumped.
I did read that you can't bind an object directly that's why I am trying to bind to the user_id property of the holiday object. I did suspect the holiday object my be out of scope but that doesn't seem to be the case. Perhaps I am accessing the user_id property incorrectly?
When I click submit and follow debug through to my controller user_id is just sent through as null.
I hope that's enough info - let me know if I need to provide more.
Thanks!

Frankie, try adding the th:field attribute to the select object instead of putting it in the option. Like this:
<select name="user_scroll" th:field="*{user_id}">
Notice the SPel syntax. Starts with an asterisk instead of $ and says user_id instead of holiday.user_id. You can access the field directly this way, since you already have defined it as your selected object in the form definition using
th:object="${holiday}"
This will also bind the selected value to the user_id property of your backing object and should solve the problem.

How to Get an id in jsp instead of value?

how to get button id from jsp to servlet instead of getting the button value
<input id="${section.id}" type="submit" name="submit" value="Edit">
how to get that id in servlet?

You can't that id is for client side use only. You will need to set the name or value to match the id of the element.
Alternatively as a workaround you could create a hidden input field that contains the id value by adding something like this to your JSP:
<input type="hidden" name="submit_id" value="${section.id}" />
This will then be available in the servlet upon form submit under the submit_id parameter.
String submitId = (String)request.getParameter("submit_id");

The only way you would be able to do that is by intercepting the form submit using javascript and setting the id as an extra post/get parameter.

the only way is make a javascript function that change your button value for the id , but i dont know why you want to do that, you could use a hidden input to send the data in the form
<input type="hidden" name="id" value="the_id_number" />

You cannot get any button id value to servlet. When a request from browser is submitted, all the input fields(input tag) will be transferred to server.The value of each input attribute can be accessed using the name of that field.All other fields like id, class etc are used for css and JavaScript functionalists.You should not design to pass the button id to server side.Think of other methods like hidden input fields

How can I call setParameter in a request object?

This is probably due to my misunderstanding and incomplete information of JSP and JSTL. I have a web page where I have input elements such as
<input name="elementID" value="${param.elementID}"/>
When I am trying to save the form, I check for that elementID and other elements to conform to certain constraints "numeric, less than XXX". I show an error message if they don't. All the parameters are saved and user does not need to type it again after fixing the error.
After saved, when I am redirecting to the same page for the object to be edited, I am looking a way to set the parameter like request.setParameter("elementID",..) Is there a way to do this ? However the only thing I can find is request.setAttribute.

HTTP responses does not support passing parameters.
JSP/Servelets allows you to either use request.setAttribute or session.setAttribute for that purpose. Both methods are available when processing the page you're redirecting to, So basically, you got it right...
Also, from what you describe, you may want to check client-side validation: don't submit the form until you're validating it using client-side scripting (javascript)

After the servlet processes the form, (ie. saves the user input in the database), have the servlet forward (not redirect, because that would lose the request params) the request to the same jsp which contains the form. So there is no need to set the params since the servlet is just passing back the same request object.
The jsp which contains the form should have inputs similar to this:
<form>
...
<input type="text" value="${elementid}"/>
...
</form>
The syntax ${varname} is EL. So if the elementid already has a value, it that textfield will contain that value. Alternatively if you have not used EL and/or JSTL, you use scriptlets (but that is highly unadvisable, EL and/or JSTL should be the way):
<form>
...
<input type="text" value="<%= request.getParameter("elementid") %>"/>
...
</form>

I had to include <%# page isELIgnored="false"%> to my jsp to allow code like ${elementid} to work

How do I send data between servlets?

I am pretty new to servlets and web development in general.
So basically I have a servlet that queries a database and returns some values, like a name. What I want is to turn the name into a link that opens a details page for that name (which another servlet would handle). How can I send the name to the other servlet so it can query a database for the relevant details?
Maybe I'm taking the wrong approach?
Edit: I am using Tomcat 5.5

Pass it as request parameter.
Either add it to the query string of the URL of the link to the other servlet which is then available by request.getParameter("name") in the doGet() method.
link
Or add it as a hidden input field in a POST form which submits to the other servlet which is then available by request.getParameter("name") in the doPost() method.
<form action="otherservlet" method="post">
<input type="hidden" name="name" value="${name}" />
<input type="submit" />
</form>
See also:
Servlets info page - contains a Hello World

Not sure if I understand correctly, but you may look at javax.servlet.RequestDispatcher and forward the url to the second servlet.
The url could be created using the name:
http://myhost.mydomain/my.context/servlet2.do?name=John

I would create the URL either in the first servlet or in a client using a configurable template for the URL. This way both servlets are clearly separated - you can even have each one on different machine.