Requirement of JSTL when studying Java EE

2018-07-12 06:45 Satnam123 imported from Stackoverflow

Does I need to study JSTL in java EE. I'm studying java EE, does studying JSTL gives any advantage if it is not a part of java EE. Thanks in advance.

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VideoPlayer widget keeps on giving Null pointer exception of invoking a virtual method on a null object reference

Right now I am trying to play the video in the start of my App as welcome greetings I followed this Video player link before adding the controller. I wrote the following code and it ran successfully in a separate activity.

public class MainActivity extends AppCompatActivity {

private static final String VIDEO_SAMPLE = "tacoma_narrows";
private VideoView mVideoView;

@Override
protected void onStart() {
    super.onStart();

    initializePlayer();
}

@Override
protected void onStop() {
    super.onStop();

    releasePlayer();
}

@Override
protected void onPause() {
    super.onPause();

    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N) {
        mVideoView.pause();
    }
}



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mVideoView = findViewById(R.id.videoview);


}

private Uri getMedia(String mediaName) {
    return Uri.parse("android.resource://" + getPackageName() +
            "/raw/" + mediaName);
}
private void initializePlayer() {
    Uri videoUri = getMedia(VIDEO_SAMPLE);
    mVideoView.setVideoURI(videoUri);
    mVideoView.start();
}
private void releasePlayer() {
    mVideoView.stopPlayback();
}}

but when I tried to add the same code in my welcome screen then I got the following message

java.lang.RuntimeException: Unable to start activity ComponentInfo{sterlingtechsolutionpk.buttonbutton/sterlingtechsolutionpk.buttonbutton.Welcome_Screen}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.VideoView.setVideoURI(android.net.Uri)' on a null object reference

The .xml file is

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/frameLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/loading_screen"
android:minHeight="177dp"
tools:context="sterlingtechsolutionpk.buttonbutton.Welcome_Screen">

<!-- The primary full-screen view. This can be replaced with whatever view
     is needed to present your content, e.g. VideoView, SurfaceView,
     TextureView, etc. -->

<!-- This FrameLayout insets its children based on system windows using
     android:fitsSystemWindows. -->

<ProgressBar
    android:id="@+id/start_progres"
    style="@android:style/Widget.ProgressBar.Horizontal"
    android:layout_width="240dp"
    android:layout_height="30dp"

    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="362dp"
    android:indeterminate="false"
    android:progressBackgroundTint="#fff200"
    android:progressTint="#005cef"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.455" />
<VideoView
    android:id="@+id/startingvideo"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_margin="8dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintDimensionRatio="4:3"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"/>

Any Help regarding this is appreciated.

Java WeakHashMap with immutable key

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How the value of i calculates as arr[5]=13,arr[6]=0?
How operator precedence works from the below code snippet
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int arr[] = new int[10];
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convert JSP EL byte[] to image?
I have a jsp page like below:
```
<c:forEach var="employeeVO" items="${list}">

    <img src="data:image/jpeg;base64,${employeeVO.employee_pic}" alt="Card image cap"/>
    <h5>${employeeVO.employee_position}</h5>
    <p>${employeeVO.employee_salary}</p>

</c:forEach>       
```
where ${employeeVO.employee_position} and ${employeeVO.employee_salary} work just fine as they are both String type
my question is ${employeeVO.employee_pic} this would return byte[] which I don't know how to covert it as a legit source?
when I check the page source code it shows like this:

src="data:image/jpeg;base64,[B@59e9139b"

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How to simulate jsp:param in SpringMVC
I have a jsp file with use jsp:include to include another jsp
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    <jsp:include page="/WEB-INF/jsp/bug/bugQueryFilter.jsp">
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        <jsp:param value="collapseOne" name="collDIVName"/>
        <jsp:param value="bugSearchVO" name="parameterName"/>
    </jsp:include>
```
In the bugQueryFilter.jsp I use ${param.collDIVName} to get the parameter.

Now I face a problem,I need to return bugQueryFilter.jsp in SpringMVC directly,but I do not know how to pass the parameter to it
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public String changeFilter(HttpServletRequest request){
   request.setAttribute("collDIVName","collapseOne");//in this way ${param.collDIVName} will not get the parameter
   return "bugQueryFilter.jsp";
}
```
Now I want to know how the simulate jsp:param to pass parameter to the bugQueryFilter.jsp page directly?

Note:due to some reason,I can not change ${param.collDIVName} to ${collDIVName} when access parameter

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Securing Image URL and images

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For download link we used anchor tag as follows:

<a href ="/wallpapers/{skuid of the wallpaper}.jpg" download>Download</a>

And while displaying each Wallpaper, there is a field where this SKU id is displayed. And all the sku ids are in sequence.

SAMPLE SKU ID LIST

If a person purchases the any two wallpapers then he can easily figure out the other wallpapers and can easily download other wallpapers

Propose solutions that the end user cannot figure out the WALLPAPERS links.

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How to modify and set the post request body using servlet filter

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My customer sent one HTTP request with URL http://example.com/callback#id_token=data Now I need handle this request and get data of "id_token". Please help me handle this request using Java web project. I tried with servlet but not get data of "id_token" My servlet is below
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<servlet>
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    <servlet-class>com.admin.controller.CallbackServlet</servlet-class>
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<servlet-mapping>
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```
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Can't access different JSP files from index with servlet

I'm trying out to set up a simple web app with TomCat, there is a servlet that's supposed to link my index page with a 2 buttons pointing at 2 different JSP.

The thing it does is when I click on those buttons it doesn't change the page, it only puts the name of the Servlet "request" (sorry don't really know the exact term).

Also when I tried to access directly by typing for example localhost:8080/reunion.jsp to access the pages directly it stays on index as if it's the only page there even if it looks like it's trying to load another page.

Here is the code of the Servlet and Index.

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/Servlet")
public class Servlet extends HttpServlet {
    private ServletContext sc = this.getServletContext();

    public void init(ServletConfig config) throws ServletException{
        super.init(config);
        sc = this.getServletContext();
    }

    public Servlet(){
        super();
    }


    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String op = request.getParameter("operation");

        if (op.equalsIgnoreCase("cv")){
            this.versPersonne(request, response);
        }
        if (op.equalsIgnoreCase("reunion")){
            this.versReunion(request, response);
        }

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


    }

    private void versReunion(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        RequestDispatcher rd = sc.getRequestDispatcher("/reunion.jsp");
        rd.forward(request, response);
    }

    private void versPersonne(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        RequestDispatcher rd = sc.getRequestDispatcher("/cv.jsp");
        rd.forward(request, response);
    }


}

Here is the index

<%@ page contentType="text/html;charset=UTF-8" %>
<html>
<head>
  <title>$Title$</title>
</head>
<body>

<form action="Servlet?operation=cv" method="post">
  <br><input type=submit value="Page personne"/>
</form>

<form action="Servlet?operation=reunion" method="post">
  <br><input type=submit value="Page réunion"/>
</form>

</body>
</html>

And just in case here is the web.XML file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <servlet>
        <servlet-name>Servlet</servlet-name>
        <jsp-file>/index.jsp</jsp-file>
    </servlet>
    <servlet-mapping>
        <servlet-name>Servlet</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>

</web-app>

My JSP files are all in the web folder.

I looked really hard for an answer and tried many different things and configurations but can't seem to find an answer.

I do think the problem lies with the servlet configuration somehow but can't really find the answer.

UPDATE : Thanks to the first answers I deleted the XML file and updated the DoGet Method. At this point the web app does try to switch pages but it throws me a 500 Error Exception telling me that it failed to instantiate the servlet here is the log :

javax.servlet.ServletException: Erreur à l'instantiation de la classe servlet [com.example.Servlet]
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:491)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:668)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:764)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1388)
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:844)

And the root cause :

java.lang.NullPointerException
javax.servlet.GenericServlet.getServletContext(GenericServlet.java:123)
com.example.Servlet.<init>(Servlet.java:15)
java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:491)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:668)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:764)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1388)
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:844)

This is the project structure :

https://imgur.com/a/YTpq4hD

Thanks in advance for your answers !

Concatenate two variables to check null condition using JSTL tags

I am trying to send image of each user separately in ModelMap

model.addAttribute("profileImage"+i, sb); // I have added attribute in loop

Variable 'i' is an index for each image which I am iterating for each user.

Now I am Having profileImage0,profileImage1,profileImage2 and so on.

While Accessing I am putting some condition

<c:choose>
    <c:when test="${profileImage!=null}">
    <center><img src="${profileImage}"  id="${profileImage}" class="rounded-circle img-circle img-responsive" style="height:90px;width:90px;" alt="Avatar">
    </c:when> 
    <c:otherwise>
    <center><img src="${pageContext.request.contextPath}/resources/images/defaultuserprofile.png"  id="${profileImage}" class="rounded-circle img-circle img-responsive" style="height:90px;width:90px;" alt="Avatar"></center>
    </c:otherwise>
</c:choose>

So in the Above Code I need to append some indexing to a variable which will first initialize the value of a variable then use it properly instead using like this one.

like profileImage0,profileImage1 and so on....

how to create form that has multiple checkbox in hybris

I have to create a form that has two radio buttons, one input field, I am able to create an input field but I'm not able to create radio buttons.

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Requirement of JSTL when studying Java EE

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