What’s JSP? Introduction to Jakarta Server Pages | Siege Tech

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Jakarta Server Pages (previously JavaServer Pages) is a regular Java know-how that builders use to write down dynamic, data-driven net pages for Java net functions. JSP is constructed on Java Servlet (alias Jakarta Servlet) and is without doubt one of the Java net applied sciences included for ongoing assist and updates in Jakarta EE.

JSP and servlets usually work collectively, particularly in older Java net functions. From a coding perspective, the obvious distinction between JSP and servlets is that with servlets you write Java code after which embed client-side markup (corresponding to HTML) into that code. With JSP, you begin with client-side script or markup, then embed JSP tags to attach your web page to the Java backend.

Consider JSP as a means of writing markup with superpowers to work together with the backend. Usually, the HTML markup is shipped to the shopper the place it interacts with the back-end server through JavaScript. JSP preprocesses the HTML with particular instructions to entry and use the capabilities of the server, then sends that compiled web page to the shopper.

JSP and JSF

JSP is carefully associated to JSF or Jakarta Server Faces (previously JavaServer Faces). JSF is a Java specification for constructing Mannequin View Controller (MVC) net functions. It’s the usual for Java net frameworks like Eclipse Mojarra, MyFaces and PrimeFaces. Whereas it is not unusual to see JSP used because the front-end for older JSF functions, Facelets is the view know-how of alternative for contemporary JSF implementations.

Do builders nonetheless use JSP?

Builders nonetheless use JSP for some functions. It is a easier know-how than extra fashionable approaches like Jamstack or a template engine like Thymeleaf, however typically easy is the best way to go.

JSP is a core Java net know-how. As builders, we will create JSP pages comparatively shortly and simply, they usually interface completely with servlets in a servlet container like Tomcat. You can say that JSP is the Java ecosystem equal to PHP and ASP within the .NET world.

You may discover JSPs in older Java net functions. Infrequently, you should still discover it helpful for creating easy and dynamic Java net pages. As a Java developer, you have to be conversant in JSP and the right way to use it in your packages.

Write JSP pages

A easy JSP web page consists of HTML markup embedded with JSP tags. JSP recordsdata have the extension .jsp. The JSP server (additionally referred to as a JSP container) is configured to direct an HTTP request to a particular JSP web page, which is then accountable for producing an HTTP response.

When the request arrives, the file is processed on the server and the HTML is rendered as the appliance’s view, an online web page. The embedded JSP tags shall be used to name server-side code and knowledge. The ultimate product of JSP is normal HTML that the shopper browser can perceive as is. The diagram in Determine 1 exhibits the interplay between HTML, JSP, and the net utility server.

Diagram of a Jakarta Server Pages (JSP) page in a web application. IDG

Determine 1. Overview of a Jakarta Server Pages (JSP) web page in an online utility.

Itemizing 1 exhibits a easy JSP web page.

Itemizing 1. A easy JSP web page


<html>
  <physique>
    <p>$2 * 2 ought to equal 4</p>
  </physique>
</html>

Right here, you see a block of HTML that features a JSP expression, which is a Java server command written utilizing Expression Language (EL). within the expression $2 * 2the $ is the JSP syntax for interpolating code into HTML. The greenback signal with braces tells the JSP processor, “Wait a second, we’re about to start out speaking about one thing particular that it’s essential to repair.” When executed, the JSP web page will output the outcomes of executing no matter is contained in the expression. On this case, the output shall be quantity 4.

JSP within the servlet container

JSP pages should be applied inside a servlet container. To implement a Java net utility based mostly on JSPs and servlets, you may bundle your .jsp recordsdata, Java code, and utility metadata right into a .struggle file, which is a straightforward .zip file with a standard net utility construction.

After getting loaded the JSP into your servlet container, will probably be compiled right into a servlet. JSPs and servlets share related traits, together with the power to entry and reply to requested objects.

How you can use JSP with Tomcat

We’ll use a pattern utility on Tomcat to get you began with the Jakarta server pages. In case you do not have already got Tomcat put in, go to the Tomcat obtain web page and choose the Tomcat set up to your working system. On the time of this writing, Tomcat 10 is the present model, supporting Jakarta Servlet 6 and Jakarta Server Pages 3.1.

You’ll be able to set up Tomcat as a Home windows service or run it from the command line with /bin/catalina.sh begin or /bin/catalina.bat. Both means, begin Tomcat, then go to localhost:8080 to see the Tomcat welcome web page proven in Determine 2.

jsp tomcat welcome page IDG

Determine 2. The Tomcat welcome web page.

Implicit objects in JSP

On the Tomcat welcome web page, click on the examples hyperlink, then click on JSP Examples.

Then open the Execution of implicit objects Internet Software. Determine 3 exhibits the output of this pattern utility. Take a minute to review the output. The weather it describes are all the time out there by default inside a JSP web page.

Sample output for a JSP page. IDG

Determine 3. Pattern output for a JSP web page.

Observe that no code modifications are required between JSP 2.0 and JSP 3.0, which is the present replace for Jakarta EE. The implicit object instance makes use of JSP 2.0.

Request parameters

Implicit objects they’re built-in objects accessible via a JSP web page. Once you’re creating an online web page, you may use these objects to entry issues like request parameterswhich is the information despatched from the shopper browser when issuing an HTTP request.

Take into account the browser URL for the Implicit Objects utility: http://localhost:8080/examples/jsp/jsp2/el/implicit-objects.jsp?foo=bar.

Please be aware that there’s nothing particular about this web page; we’re simply utilizing it to see how the URL parameter is accessed. The parameter is ?foo=barand you may see it mirrored within the output of the net web page, the place the desk exhibits EL expression and the worth is bar. To check this, change the URL to http://localhost:8080/examples/jsp/jsp2/el/implicit-objects.jsp?foo=zork, press Get intoand you will notice the change mirrored within the output.

This instance is a quite simple introduction to utilizing JSP tags to entry server-side request parameters. On this case, the JSP web page makes use of the built-in (implicit) object referred to as param to entry the request parameters of the net utility. the param The thing is obtainable inside the JSP expression syntax you noticed in Itemizing 1. In that instance, we use an expression to do some calculations: $2 * 2which resulted within the output of 4. On this case, the expression is used to entry an object and a area on that object: $param.foo. Subsequent, we are going to take a more in-depth take a look at the instance of implicit objects.

JSP in an online utility

On the Implicit Objects web page, click on the again arrow, adopted by the Font Hyperlink. It will take you to the JSP code for the Implicit Objects net utility, proven in Itemizing 2.

Itemizing 2. JSP code for the Implicit Objects net utility


<%@web page contentType="textual content/html; charset=UTF-8" %>
<%@ taglib prefix="fn" uri="http://java.solar.com/jsp/jstl/features" %>

<html>
  <head>
    <title>JSP 2.0 Expression Language - Implicit Objects</title>
  </head>
  <physique>
    <h1>JSP 2.0 Expression Language - Implicit Objects</h1>
    <hr>
    This instance illustrates among the implicit objects out there
    within the Expression Language.  The next implicit objects are
    out there (not all illustrated right here):
    <ul>
      <li>pageContext - the PageContext object</li>
      <li>pageScope - a Map that maps page-scoped attribute names to
          their values</li>
      <li>requestScope - a Map that maps request-scoped attribute names
          to their values</li>
      <li>sessionScope - a Map that maps session-scoped attribute names
          to their values</li>
      <li>applicationScope - a Map that maps application-scoped attribute
          names to their values</li>
      <li>param - a Map that maps parameter names to a single String
          parameter worth</li>
      <li>paramValues - a Map that maps parameter names to a String[] of
          all values for that parameter</li>
      <li>header - a Map that maps header names to a single String
          header worth</li>
      <li>headerValues - a Map that maps header names to a String[] of
          all values for that header</li>
      <li>initParam - a Map that maps context initialization parameter
          names to their String parameter worth</li>
      <li>cookie - a Map that maps cookie names to a single Cookie object.</li>
    </ul>

    <blockquote>
      <u><b>Change Parameter</b></u>
      <kind motion="implicit-objects.jsp" technique="GET">
          foo = <enter kind="textual content" identify="foo" worth="$fn:escapeXml(param["foo"])">
          <enter kind="submit">
      </kind>
      <br>
      <code>
        <desk border="1">
          <thead>
            <td><b>EL Expression</b></td>
            <td><b>Consequence</b></td>
          </thead>
          <tr>
            <td>$param.foo</td>
            <td>$fn:escapeXml(param["foo"])&nbsp;</td>
          </tr>
          <tr>
            <td>$param["foo"]</td>
            <td>$fn:escapeXml(param["foo"])&nbsp;</td>
          </tr>
          <tr>
            <td>$header["host"]</td>
            <td>$fn:escapeXml(header["host"])&nbsp;</td>
          </tr>
          <tr>
            <td>$header["accept"]</td>
            <td>$fn:escapeXml(header["accept"])&nbsp;</td>
          </tr>
          <tr>
            <td>$header["user-agent"]</td>
            <td>$fn:escapeXml(header["user-agent"])&nbsp;</td>
          </tr>
        </desk>
      </code>
    </blockquote>
  </physique>
</html>

JSP features

In case you’re conversant in HTML, then the code in Itemizing 2 must be pretty comprehensible. You’ve the anticipated HTML <td> objects, adopted by $ JSP expression syntax introduced in Itemizing 1. However discover the price by param.foo:


<td>$fn:escapeXml(param["foo"])&nbsp;</td>

Right here the fn:escapeXML() it’s a JSP operate.

A JSP operate encapsulates a chunk of reusable performance. On this case, the performance is to flee XML. JSP presents a wide range of features, and you may as well create features your self. To make use of a operate, you import its library into your JSP web page, then name the operate.

In Itemizing 2, we embrace the escapeXML operate with the next line:


<%@ taglib prefix="fn" uri="http://java.solar.com/jsp/jstl/features" %>

The syntax is fairly easy: import the required features and assign them a prefix (on this case “fn“) which can be utilized in all the following expressions.

The Jakarta Commonplace Tag Library (JSTL)

The import line in Itemizing 2 calls taglibwhich is the abbreviation for tag library. On this case, we’ve imported the Jakarta Commonplace Tag Library (JSTL). Tag libraries outline reusable bits of performance for JSPs. JSTL is the usual tag library, which accommodates a set of tags which might be shipped with each servlet and JSP implementation, together with Tomcat.

The “features” library is simply one of many tag libraries included with JSTL. One other frequent taglib is the core library, which you import by calling:


<%@ taglib uri = "http://java.solar.com/jsp/jstl/core" prefix = "c" %>

I prefer it "fn"the "c" the designation is typical; you may see it on most JSP pages.

Defending JSP pages with JSTL

The next instance tag is from the JSTL core library:


<c:out worth = "$'<div>'"/>

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