JSP: Practical Guide for Programmers
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Java Servlet Tutorial for Beginners. Java Servlet Filter. Java JDBC. And do not handle the security of the pages. If you want to have an application, secure each page, please refer to the article below:. Create a simple Login application and secure pages with Java Servlet Filter. Never allow users to directly access to your JSP page. The question becomes:when to write a JSP and when to just write a servlet? But I digress. The answer is: It really depends on the purpose. For mostly layout concerns,it is wiser to write a JSP and access the information necessary through scriptlets,custom tags,or JavaBeans.
This was usually not the case when using servlets since presentation and logic were commonly used in the infamous out. Using JSPs,the presentation then stays mostly separate from the logic. Having a lot of logic code inside JSPs makes for some interesting read:frustrat- ing debugging sessions. While there are many good things about the JSP technology,there are a few drawbacks. The problemwith this is that if you have page designers who have little or no programming background,working with the JSP can blur the line between the separation of content and logic. This can lead to maintenance issues,not to mention debugging issues.
With the use of scriplets in JSPs,it became easy to mix Java code—which more than likely is busi- ness logic—into the presentation. Using expressions,the value of the expression can be written to the client response. Even way back in about which is like three lifetimes ago for most developers ,when JSPs were becoming recognized as a preferred way to develop the presentation tier,it was already becoming apparent that the need for using JavaBeans was commonplace.
At least it separated the role of the JSP page author fromthat of the Java developer. By taking advantage of customtags,the page author was able to concentrate on presentation features,while the Java developer was able to code the necessary logic and present it back to the page author in an easy to use tag. In short, customactions started us back on the path of readability,reusability,and maintainability.
By doing so,actions usually affect the existing output streamby performing some logic. A number of standard actions were introduced in JSP v1. A custom action is invoked by using a custom tag in a JSP page. A tag library is a col- lection of custom tags. One of the advantages of using a custom tag over,for exam- ple,a JavaBean,is that when using custom tags you get access to the context and JSP scope objects.
These include the request,response,session,and attributes that we are all familiar with. Before the availability of custom actions, JavaBeans components in conjunction with scriptlets were the main mechanism for per- forming such processing within JSPs. However,there were a couple of disadvantages to using JavaBeans. For one,the pages became more complex. Custom actions alleviated these problems by abstracting the functionality.
Custom actions encapsulate recurring tasks. By doing so,they can be reused across more than one application. Custom actions also increase productivity by encouraging division of labor between library developers and library users. Java developers,and not page authors, usually create JSP tag libraries.fensterstudio.ru/components/tyhizomu/sojyz-rastrear-un.php
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JSP tag libraries are used by web application designers who can focus on presentation issues rather than being concerned with howto access databases and other enterprise services. A TLD con- tains information about the library as a whole and about each tag contained therein. The HelloTag will print a personalized hello to the JspWriter which is the output stream for a JSP if an optional name attribute is provided.
The next step is to create your tag handler. This would be the jstlpg.
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It is a standard naming convention, although not required,to name your tag handler class by the name followed by Tag to indicate that it is a tag handler. TagSupport is the base class used for simple tags. It can be found in the javax. What your tag actually does depends on what methods of the Tag interface could potentially be called and what must be implemented.
TagSupport is a utility class that supplies a default implementation for the lifecycle methods. We will rely on the default implementation provided in the TagSupport class for the implementation of the remainder of the interface. The container will call the set- ter method on any attribute encountered for the custom action. Therefore,it is required that a public setter method be present in your handler. That is why we see a setName method in our handler. It is here that we determine if a name attribute has been set so that we know how to send output to the current JspWriter.
For example,a database connection would qualify here as a resource. It is also possible to reset any state that might be necessary. Some of the more advanced features of tags,like using scripting variables,are made much easier through the JSTL. Typically an attribute is passed to the tag that contains the ID of the object to be used. The usual operation is that the tag handler retrieves a scripting variable value object using pageContext.
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One tag by itself is not very interesting. What we really want to do is combine tags that have common functionality into libraries. Custom tag libraries are collections of custom tags that usually fall within the same functional area. If we rewrite our hello. It became clear that the use of custom actions was a way to start to reuse code,keep JSPs cleaner in terms of embedded code, and preserve the MVC model better.
Throughout this evolution,JSPs have been improving at their core reason for existing. That reason is,again,the clean separation of presentation and business logic. In my opinion,the adoption of custom tag libraries has been slower than it should have been since their introduction. The most likely reason for this is that,as we can see fromour sample,it still takes a fair amount of coding effort to create a custom tag library. It would be better,more cost effective,and quicker if page authors could learn a set of customtags once and then just reuse them.
We have seen how you can write your own servlet that does the same thing that a JSP can do,assuming you are a Java programmer,and then abstract and encap- sulate some of that required functionality into customactions. To put it simply,JSTL provides the functionality and you provide the purpose. Saying hello to our friend is shown in Example 1. This is exactly the same function- ality that we previously had to code a TLD and tag handler for.
If we really wanted to get crazy,we could utilize one more JSTL tag and make our simple JSP into a completely internationalized page ready for any language that our clients might be using and we have translated strings for. A whole new way of writing JSPs will unfold before your very eyes. This is just the beginning of the power of the JSTL actions. Effectively,if we take out the HTML,we have accomplished quite a bit in just a handful of lines. We have declared use of the JSTL tag libraries,accessed data froma resource bundle,pulled out a parameter from the HTTP request,and determined what is the correct message to display to our output stream.
Think back to the amount of servlet code we looked at to accomplish just some of this! Reviewing these basics sets the foundation for us to talk about actions in more detail. I also assume that you are familiar with the JSP technology referred to throughout this book,and therefore you already have the working environment for JSP development. You can use any web application server you choose, as long as it supports JSP 1.
Here is what we cover in the Course
The Taglibs project is an open-source repos- itory for JSP custom tag libraries and associated projects. It is possible to download either the binary distribution of the RI or the entire source for the Taglibs project. If you download the entire source,you will get source to tag libraries other than those included in the standard project.
It is up to you what you want to do. You should be able to point your browser to your server and access the application as standards-examples. You should have a screen that looks similar to Figure 2.
The sample application uses the MySQL database. Once you have the database downloaded,place the drivers in your classes directory of Tomcat. Then just click the databaseinit. It will create and initialize the necessary tables and data that are used throughout the book. A JSP page can access,create,and modify server-side objects. These objects can be made visible to standard and custom actions,as well as to scripting elements.
As soon as the response is sent back to the client or the request is forwarded , all references to the object are released. Objects with request scope are accessible fromall pages that are processing the same request.