Suppose an example. I have following interface:
public interface DataSource<T> {
Future<T> fetch();
}
This datasource can do asynchronous data fetching. And we have following tag for using datasource in JSP:
<html>
<d:fetch from="${orderDS}" var="orders">
<c:foreach in="${orders}" var="order">
<div class="order">
<c:out value="${order.title}" />
</div>
</c:foreach>
</d:fetch>
</html>
So, what I want? I want JSP rendering engine to call my custom tag (FetchTag in this example) twice. On first call FetchTag will do DataSource.fetch() call and save Future locally as a object field. On second call FetchTag do Future.get() call and will be blocked until data becomes available.
Is there any way to do such a thing?
I think a better design would not try to alter JSP rendering. Put all that database code on the server side, where it belongs, and use an AJAX call to get that data from a server-side component.
In general, I've found that embedding stuff in custom tag libraries is a bad idea. JSTL and/or Spring tag libraries are all that I need. If I feel like my UI needs to do more, I'm thinking about it incorrectly.
For JS disabled clients, I'd just make them do the round trip for the data and not try to do it in the background. Give them a choice: wait or turn on JS.
Related
So I have a .jsp page which has a form on it, like this (naturally this is a massive simplification):
<form:form commandName="myCommand" method="post">
<form:select path="values" class="select-tall" multiple="multiple" id="mySelect">
<option>first</option>
<option>second</option>
<option>third</option>
</form:select>
<button type="submit" class="button">Save</button>
</form:form>
When the submit button is pressed, the form is submitted(somehow) and the path= attributes are used to bind the data inside the form elements to the properties of an instance of a plain old java object. I understand how this POJO is specified, and I understand how the POST request is routed to the correct controller, but I don't understand where or how the form values are mapped to the given POJO.
What I don't understand is:
How does the spring tag library modify the form such that this binding takes place?
How would one go about doing this in a manual or ad-hoc fashion(using a Javascript onSubmit() method, say)?
Essentially my question is: How does the spring-form.tld tag library work?
Any resources, or even a high-level explanation in your own words, would be extremely helpful.
I've implemented a work-around solution in the mean time (dynamically adding items to a hidden form element), but I feel like this is hack-y and the wrong solution.
I have been using JSTL to fetch values from my database and display it in my jsp page using a similar code as shown below.
<sql:setDataSource
var="myDS"
driver="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/mydb"
user="root" password="secret"
/>
<sql:query var="list_users" dataSource="${myDS}">
SELECT * FROM users;
</sql:query>
<c:forEach var="user" items="${listUsers.rows}">
<c:out value="${user.name}" />
<c:out value="${user.email}" />
<c:out value="${user.profession}" />
</c:forEach>
My team leader advised me that it is not a good practice to put queries in the jsp page directly. Since there is a database name and username and password in this code I'm not sure if this code implements proper security. I would like to know your thoughts on the matter, and if there is any alternative to do this using JSTL itself.
Since JSTL is executed on server side, there's no security hole because the query cannot be seen by clients of the application. There are other problems with this approach:
The query is not reusable. If you need it in other pages, you will need to repeat the query. When you have simple queries like this one you cannot check the problem, but this arises with more complex statements that needs parameters as well.
You're creating a connection manually per page! This will slow your application. Use a proper datasource for a database connection pool configured as a resource or programatically (C3PO or BoneCP, for example)
Move all your database code into proper Data Access Layer classes. And use <sql> for JSTL for learning purposes only, not for real world applications.
More info:
How to use JSTL sql tag
Retrieve values from JDBC and use JSTL tags to call the methods
Should a database connection stay open all the time or only be opened when needed?
You should really do your query in your java class, not in the jsp, like your team leader advised.
On the security side it doesn't really matter, all the code is available on the server, jsp or java. The sql tag shouldn't output that information in the generated page.
But really the question is more about the right use of the technologies:
jsp is used as a template, it should take data and show them to the end user. Some basic operation can be done life looping on data list or formating data, but this should be only specific to the view you want to make
java controler is used to recuperate data and configure the view as needed like which jsp to use and which data to send in that jsp
Some background: I am building a custom JSF component. The component is basically a text editor and it should have a "Save" -button for saving the content string of the editor. As I am using the CodeMirror library, I need to fetch the content (string) from the editor with javascript and send that to the server. Therefore, in this case I cannot use XML-based JS invocation such as f:ajax.
The question: I was planning to send the string with jsf.ajax.request, but it doesn't directly support calling methods on beans. How can I invoke a method in a bean with JSF in AJAX manner?
There at least two ways to get around this:
Include a hidden form to page with hidden inputfield. Update that inputfield from javascript and then call jsf.ajax.request to post that form. Custom actions can be invoced in the property's getter or setter if needed.
Do the request with raw XMLHttpRequest (or maybe with help from some other JS library). Create a servlet and call that.
Both ways are clumsy and the latter also breaks out of JSF scope.
Am I missing something? How do you do these?
There is a quite similar question, but the answers given only refer to XML-based AJAX invocations. There is also another similar question, but that refers to XML-based AJAX calls as well.
I couldn't find out how to call beans direcly with javascript, but here is a hack around calling f:ajax-declaration from javascript:
1) Create a hidden form with fields for all the data that you want to send to the server. Include a h:commandButton as well:
<h:form id="hiddenForm" style="display: none;">
<h:inputHidden id="someData" value="#{someBean.someData}" />
<h:commandButton id="invisibleClickTarget">
<f:ajax execute="#form" listener="#{someBean.myCoolActionOnServer()}" />
</h:commandButton>
</h:form>
As usual, listener attribute, #{someBean.myCoolActionOnServer()} in this case, refers to the method that you want to execute on the server.
2) In some other button use onclick to call for your special javascript AND click the trigger-button via javascript:
<h:commandButton value="Click me" onclick="populateTheForm('hiddenForm'); document.getElementById('hiddenForm:invisibleClickTarget').click(); return false;" />
populateTheForm() should actually fill the data into hiddenForm's fields.
This is a simplification of my case but should work. Still looking for more conventient approach, though.
I did this task several times. Yo don't need multiply hidden fiels. You can use only one hidden field, convert all input values to JSON object via JSON.stringify and set into this field. On the server side - deserialize JSON object (there are many Java libs for that) to an Java class. That's all.
is there a way to use groovy builders to build JSP files in a Grails application keeping things enough integrated?
To explain better: by default Grails uses gsp files that are nice but quite verbose..
<div class="clear">
<ul id="nav">
<li><g:link controller="snippets" action="list">Snippets</g:link></li>
<li><g:link controller="users" action="list">Users</g:link></li>
<li><g:link controller="problems" action="list">Problems</g:link></li>
<li><g:link controller="messages" action="list">Messages</g:link></li>
</div>
<div id="content">
is there a way to use groovy.xml.MarkupBuilder tha would turn the previous piece into
div(class:'clear') {
ul(id:'nav') {
li { g_link(controller:'snippets', action:'list', 'Snippets') }
// and so on
Of course g_link is invented just to give the idea..
Do a search for builder under the web layer section of the grails user guide. There is an example in there that shows you exactly how to do this using the xml builder.
I don't have a complete answer for you, but I suspect the key will be gaining access to the "view resolvers". In a normal SpringMVC app, these are configured in views.properties (or views.xml) as follows:
csv=com.example.MyCSVResolver
xml=com.example.MyXMLResolver
audio=com.example.MySpeechResolver
In a regular SpringMVC app, you return something like new ModelAndView(myModel, 'csv') from a controller action.
This would cause the CSVResolver class to be invoked passing it the data in myModel. In addition to containing the data to be rendered, myModel would likely also contain some formatting options (e.g. column widths).
Spring searches the views file for a key matching the view name. If it doesn't find a match, by default it just renders a JSP with the view name and passes it the model data.
Now back to Grails....remember that Grails is really just a Groovy API over SpringMVC and most of the features of SpringMVC can be accessed from Grails. So if you can figure out how to modify the views file, just change your controller actions to return an appropriate ModelAndView instance, and it should work as described above.
GSP allows you to run arbitrary Groovy code inside <% %> brackets. So you can have something like this (borrowing example from page linked to by BlackTiger):
<% StringWriter w = new StringWriter()
def builder = new groovy.xml.MarkupBuilder(w)
builder.html{
head{
title 'Log in'
}
body{
h1 'Hello'
builder.form{ }
}
}
out << w.toString()
%>
Note that the above calls g:form tag, and you can pass additional stuff to it.
So what you are asking for is certainly possible, though I am not sure if it will end up being a win. I'd suggest you perhaps look more at TagLibs in combination with Templates and SiteMesh Layouts - can definitely simplify things tremendously.
I was thinking about the idea of using Ajax instead of TagLib. The most elegant way would be: Using Java Annotation.
The idea is, designers or anybody can make the HTML without any taglib ,just using the "standard" HTML tags with id or name, and call the Javascript. That way any WYSIWYG can be used, developer don't have to care about HTML format or the way it's designed.
In many (at least open-source) WYSIWYG don't show the taglibs in that final result (or have a template of it), so it's hard to "preview". Other reason is, developer should know Java and HTML/TagLibs should not be a must-have, since we got CSS and AJAX.
It should work just like that:
MyClass.java:
import ...
// Use the ResourceBundle resource[.{Locale}].properties
#Jay2JI18n(resourceBundle="org.format.resource",name="MyClassForm")
public class MyClass {
private Integer age;
private String name
private Date dob;
private salary;
#Jay2JLabel(resource="label.name")
#Jay2JMaxLength(value=50,required=true,)
#Jay2JException(resource="exception.message")
public String getName() {
...
}
public void setName(String name) {
if ( name.trim().equal("") ) {
throw new Exception("Name is required");
}
}
/* Getter and setter for age */
...
#Jay2JLabel(message="Salary")
#Jay2JFormat(format="##,###.00",language="en")
#Jay2JFormat(format="##.###,00",language="pt_BR")
// or you could use that to access a property of the ResourceBundle
//#Jay2I18nResource(resource="money.format")
public Date getSalary() {
...
}
/* Setter for salary and getter/setter for the rest */
...
}
Page.html:
<html>
<head>
<SCRIPT>
</SCRIPT>
</head>
<body>
<form onload="Jay2J.formalize(this)">
</form>
</body>
</html>
of it can be a HTML with the fields filled;
PageWithFields.html:
<html>
<head>
<SCRIPT>
</SCRIPT>
</head>
<body>
<form action="myfavoritewaytopostthis" onsubmit="return Jay2J.validate(this)" onload="Jay2J.formalizeExistField(this)">
<label>Name</label><input type="text" name="name" id="name" />
<label>DOB</label><input type="text" name="dateOfBirth" id="dob" />
<label>Salary</label><input type="text" name="salary" id="salary" />
<input type="submit" />
</form>
</body>
</html>
That way the Annotation (no XML, it's like HTML in the way that it's only another file modify and XML is not Java) will define how the HTML will be treated. That way developer can stop developing in HTML and use just JAVA (or JavaScript), do you think that's a valid idea?
When i see your topic title i thought:
You cant use Ajax in stead of a taglib. AJAX is javascript on the client and the taglib is java code on the server.
After reading your post i thought, ah he whats to do what [link text][1] does
But then not entrily the same.
[1]: http://code.google.com/webtoolkit/ GWT
First impression is ... yuck, someone who picks this up will have no idea what they're looking at without learning your (new, different, non-standard) way of doing things. You could do something similar by implementing a tag that takes a bean (value object) and maybe does some minor reflection/annotation inspection to emit the proper html, and you'll save yourself a lot of heartache down the line.
Make your value objects implement a simple interface that your tag will use to extract and format the html, and you can probably get 80-90% of where you're trying to go with 1/2 the work or less.
First impression was, WTF. After reading further, I get a impression that you are trying to address the 'separation of concerns'problem in a different way. Some observations on your approach.
Requires client side scripting to be enabled and hence fails accessibility guide lines.
Reinventing the wheel: Many web frameworks like Tapestry, Wicket try to address these issues and have done a commendable work.
On your comment on binding Java to HTML, the code example doesn't convey the idea very clearly. formalize() seems to create the UI, that implies you have UI (HTML) coded into java (Bad Idea? probably not NakedObjects attempts to you domain models for UI, probably yes if one were to write a page specific code)
validate() is invoked on onSubmit(), Why would I want it to be processed asynchronously!! That aside, using obstrusive java script is way out of fashion (seperation of concerns again)
Your argument on taglibs preventing WYSIWIG, though justifiable, is not entirely valid. Tags cannot be used to compose other tags, each tag is a unique entity that either deals with behaviour or emits some html code. Your argument is valid for the second case. However, if I understand your formalize() correctly, you are doing the same!
Nice to hear some new ideas and Welcome to SO. Also, please use the edit question option until you earn enough reputation to add comments. Adding answers is not the right way!
This idea has some merit, if I understand it correctly.
You could use AOP to modify a servlet that would actually be called for the page. The servlet would then return the html, using the annotations.
This way the programmers don't see the html generation, and if you have a standard javascript library for it, then it may work.
But, just because it works doesn't mean that you should do it.
As was mentioned, there are many frameworks out there that can hide the javascript from programmers, such as JSF, which is basically taglibs and a different navigation scheme.
I remember using the beehive project to do something similar, it was annotation driven so I could basically do everything in java and it generated the javascript, years ago. :)