Can I create a response object in java without creating a Servlet? I have a regular java class right now called Menu. It contains not only my menus for my application but it also contains my CRUD functionality that is tied to the database. Which works fine on the console. What I want to do now is to display the result set on a webpage. I want to use AJAX (no frameworks like jQuery etc.) to capture the information from the result set. In the Menu class I am going to convert the extracted information into a Json string with Jackson databinding (object mapper). I want to use a PrintWriter to send this information back to AJAX. I am assuming I need a response object. Do I have to re-write my Menu class as a Servlet or is there another way to accomplish this?
For querying data from server you need to have a resource which has
http url
can accept a form of request as input
can give response based on business logic in menu crud class.
For this querying as you said you can do with ajax call to this servlet with specified url pattern from your frontend webpage.
In short servlet will be essential. It can handle all http method types like get post and so on.
So you can map your crud methods to your servlet methods
eg :
doGet - querying items.
doPost- creation of item.
doDelete- delete an item.
and so on.
further you will call your crud methods from these servlet do* methods.
for example refer: https://www.geeksforgeeks.org/servlet-crud-operation-with-example/
Hope this helps.
Related
I have a good basic knowledge of how to create web applications using java and jsp, together with Expression Language and JSTL. I am trying to learn how to use Angular.js for my front end.
I've gone through several tutorials, and I am starting to get a fair grip of the basics. But I have yet to figure out how to transfer data from the server, to the front end. Most tutorials I've found, describe how to send data from the front end, to the server.
I know that a RESTful api back end is recommended for Angular web apps. Unfortunately, I have no experience with this, and I find it hard to learn both angular and RESTful at the same time. If possible, I would love to make a work around, so that I can use my existing server solution, and learn one element at the time.
Server side setup
Now, in my old setup, using javax.servlet.http.HttpServlet, i call the service(HttpServletRequest, HttpServletResponse)-method. Inside the method, i add attributes to the request, like this:
request.setAttribute("attribute1", "1");
request.setAttribute("attribute2", "2");
request.setAttribute("attribute3", "3");
Then, because of a front controller pattern, I pass these request variables on to a redirect like this:
request.getRequestDispatcher("/WEB-INF/" + myPageVar + ".jsp").
forward(request, response);
For now, I would ideally like to keep this server side setup.
Current client side data access:
In the current setup, I can now access the initiated variables in two different ways. Either in a javascript script, like below (does not work with objects, only simpler attributes like strings (including JSON)). the next lines of code is picked from a jsp-page that the servlet would have redirected to.
var attribute1 = ${requestScope.attribute1};
or in the html, like this (would work with objects):
<c:set var="attribute1" value="${requestScope.attribute1}"></c:set>
I guess that I could incorporate Expression Language, and use javascript variables to initialize variables in my angular modules, directives and controllers, but I would prefer to do it purely in Angular.
Are these attributes accessible in any way, using angular? I've been trying to read up on $http, and $scope, but there is a jungle of non-relevant info on those, which I haven't been able to navigate through yet.
If the data you want to make accessible to angular should be ready when user lands on the page, it could make sense to put data in javascript variable in jsp page as you suggest.
Since your var is in global scope you can get in your angular controller like this:
$scope.att1 = attribute1;
However if you want to update your data without re-rendering the whole page (and that is what you want pretty soon) you should use $http to call a servlet that returns json. You can relatively simply make this servlet without jax-rs by overriding doGet in httpServlet and use a lightweight json lib (like gson). This example will do it:
//Set up pojo and make it into json string:
SomeClass pojo =new SomeClass();
pojo.setX("this is X");
JSONObject jsonObject = new Gson().toJson(pojo);
String jsonStr=jsonObject.toJSONString();
//Modify response and write json string
httpServletResponse.setStatus(200);//We are ok
httpServletResponse.setContentType("application/json");
httpServletResponse.setCharacterEncoding("UTF-8");
Writer writer = httpServletResponse.getWriter();
writer.write(jsonStr);
writer.close();
//Thats it
In a simple setup you handle this response in your controller like this:
$http({method: 'GET', url: 'http://yourservleturl' })
.success(function(jsonStringFromServlet){
$scope.newData = jsonStringFromServlet;
})
.error(function(){
$scope.error = true;
});
In page-html you access the data with
<div>This is your new x: {{newData.x}}</div>
Don't use jsps at all, don't set attributes.
Only use static html, thats the benefit ! You can write angular directives that perform the funcationality of jsp includes, and have much cleaner code (no embedded jstl, java. just pure html).
Create server side code that returns json. Then your angular js code calls the rest api and populates the client side model.
If you have something that needs populating on startup, use javascript appropriately.
Here is a typical java method that returns json, using Jersey (similar to Spring MVC, resteasy, restlets, spark, apache cxf etc etc) :
#PATH("/myPojo")
#GET
public Response getPojo(Long id) {
Pojo pojo = myService.getPojo(id)
return Response.ok()
.entity(pojo)
.build();
}
In angualr you can then create, for example, $myPojoService.getPojo() that is injected to relevant controllers and calls this endpoint. When called it probably returns the pojo as json and then probably populates the $scope.model.pojo json object. Then the two way databinding of angular updates your gui ... and Boom, you are a full stack engineer/ front end dev!
There are a lot of different ways to accomplish this. This is just what I ended up using.
To expose values in your JSP to Angular you'll need to write them out in script tags and build up Javascript vars with them. Then you can access them from Angular. I'm doing this to pass-in authenticated user account information from server side to my angular code. Your JSP would contain code such as:
<script>
window.CURRENT_USER = {
id: <%=currentUser.getId()%>,
name: "<%=currentUser.getName()%>",
email: "<%=currentUser.getEmail()%>",
prevLogin: new Date(<%=currentUser.getPrevLoginAt().getTime()%>),
prevLoginIp: "<%=currentUser.getPrevLoginIp()%>"
};
</script>
Then in your angular controllers, you can access it like this:
var currentUser = $window.CURRENT_USER;
A better approach (mentioned by Jacob Nicolaisen) would be to use the Google GSon library to actually generate the JSON objects instead of hand coding them.)
If I have a #Controller method whose parameter is a #RequestBody param, I usually have to write some jQuery script or something similar to perform an AJAX request with JSON object in order to call that method. If I tried calling that method via a web browser directly, it returns with a Error 415 Unsupported Media Type.
Is there any alternative to just quickly call such method using browser without having to write some jQuery code? Like perhaps a way to write the JSON object in the URL/address bar?
code:
#RequestMapping("testCall")
#ResponseBody
public List<TestObject> getTestCall (#RequestBody TestParams testParams) {
return stuff;
}
public class TestParams {
private Integer testNumber;
//getter/setter for testNumber
}
I thought maybe I could just do:
http://localhost/testCall?testNumber=1
maybe Spring would auto populate a new TestParams instance with that property set to 1 but that didnt work...
maybe I need to do something extra for that?
The whole point of a #RequestBody annotated parameters is for the Spring MVC stack to use the HTTP request body to produce an argument that will be bound to the parameter. As such, you need to provide a request body. Sending a request body is very atypical for a GET request. As such, browsers don't typically support it, at least not when simply entering an address in the address bar and submitting the request.
You'll need to use a different HTTP client, like jQuery. I typically have a small Java project in Eclipse that's setup with an Apache HTTP components client which can send HTTP requests to whatever server. It takes a few seconds/minutes to setup the correct request body and run.
I have spent the last year building a REST API, and by far the best way to exercise that API manually is using the Chrome Extension, Postman. I cannot recommend this tool enough.
https://chrome.google.com/webstore/detail/postman-rest-client/fdmmgilgnpjigdojojpjoooidkmcomcm?hl=en
To test your simple example you'll need to invoke a POST (I assume that as you have a request body, but your controller method doesn't define a HTTP Verb) using POSTMAN to your Url (like the following example):
POST /contextRoot/testCall
{
"testNumber": 1
}
If you want to test your API automatically (which I recommend), you can use the excellent Spring Mvc Test project. This allows your to call your API via a rest-like DSL and assert that the response is in the shape you want. More details can be found here:
http://docs.spring.io/spring/docs/3.2.x/spring-framework-reference/html/testing.html#spring-mvc-test-framework
you can add request params to the getTestCall method:
#RequestParam(value = "testNumber", required = false, defaultValue = "") String testNumber
There is a chrome app called Advanced REST client. You can pass the data in form of json to your controller using this chrome app. For eg. json data is
id:1,
name:"xyz"
whereas the controller can have #RequestBody Person form.
The Person class would be a POJO having id and name as instance variables. The Spring would automatically map the json data to the form.
I think this is the easiest and simplest way of checking your spring controller.
Check the extension Advanced REST client here
From what I know You can send JSON object to the webbrowser and it will be displayed without further need of AJAX.
useful tutorial:
http://www.mkyong.com/spring-mvc/spring-3-mvc-and-json-example/
is their a neat way to pass a model to jsp, render the jsp and return the html as string using Spring. The html is then used in an e-mail that is fired off programmitcally, I do not want to use freemarker, but maybe I should ?
The url being requested is part of the same app.
I want one of my service layer classes to be able to call a view and use the html as a String.
You can call requestDispatcher.include(request, response) method.
You will need to implement the request and response objects. The request object will provide all information to the dispatcher which page should be rendered, the response object you will pass to the call will then capture the result to a string (using e.g. a StringBuilder).
See e.g. this tutorial for more info.
I'm guessing a servlet filter will do the trick? Not really a Spring solution, but easy enough to do.
Also this answer seems relevant, although it is DWR that you may not necessarily want to use in this instance.
You can use Velocity to create an email template:
String text = VelocityEngineUtils.mergeTemplateIntoString(
velocityEngine, "emailTemplate.vm", model);
There is a complete chapter in the Spring reference docs of how Spring can be used to send emails of various types.
Sorry friends if this question is very easy but i am confuse i unable to find out solution.
As we all know in spring MVC framework we create controller which will handle multiple request from same page using #requestmapping annotation.
but same thing i want to do in servlet how can i do ?
Suppose i have a jsp which which will contain a jqgrid,and two forms i want to use only one servlet to load the data into jqgrid and that servlet only will handle request from both the form . Since we have only doGet and doPost in servlet how one servlet fulfill all three request. Hope you understand my question if you have and link where i get sample or and tutorial link plz reply me
Well, the only easy way to do this would be to use a request parameter to control how the processing happens.
In a very basic example, you may have something like a requestType value that gets passed as either part of the query string or the request body. You would assign values of 1-3 (or 0-2) with each value indicating a different type of request. Your servlet would then parse the request accordingly.
This actually is how the DispatcherServlet in SpringMVC works. There's only one servlet class instance and when a request comes in, it examines the query string along with other parts of the request to determine which controller should handle the request.
I'm currently developing with Struts 1 a web application. I've recently started to use AJAX technology and I'm stuck with something.
I call an action method (via AJAX) to validate my form but no values are changed in the form bean when it gets to the action method. I suppose this is because calling the action via AJAX doesn't submit the form to the action method. Am I right? I've tried to send form values as a JSON object, but I can't parse it in the action class because; as far as I know, I need an external library to do so and, unfortunately, company policies doesn't allow me to use external libraries. Is there any other way to send the form?
Thanks in advance,
Carlos
Yes, you are correct. All that's happening with AJAX is a request is being sent to a particular URL, not a form submission.
The easiest way to deal with this is to add the fields you want validated as parameters in the URL then simply pull them off the HTTP request in the server (can't remember how easy that is with Struts).
I think this will do for you.
request = $.ajax({
url :'/your_action.do',
type :'post',
cache:false,
data :$("#formId").serialize()
});
the data field will send the required actionForm attributes.