What s the difference between including files with JSP include directive JSP include action and using JSP Tag Files

Question

It seems that there are two methods for templating with JSP  Including files with one of these statements    lt    include file  foo html    gt   lt jsp include page  foo html    gt    or using JSP tag files      Save this as mytag tag  lt    tag description  Description  pageEncoding  UTF-8   gt   lt html gt   lt head gt   lt  head gt   lt body gt       lt jsp doBody  gt   lt  body gt   lt  html gt    And in another JSP page call it with   lt    taglib prefix  t  tagdir   WEB-INF tags    gt    lt t mytag gt       lt h1 gt Hello World lt  h1 gt   lt  t mytag gt    So which method should I use  Is one now considered deprecated or are they both valid and cover different use cases   Edit  Isn t using this tag file the same as using an include      Save this as product tag  lt    tag description  Product templage  pageEncoding  UTF-8   gt   lt    tag import  com myapp Product    gt   lt    attribute name  product  required  true  type  com myapp Product   gt   Product name    product name   lt br  gt  Quantity    product quantity   lt br  gt    And call it on another JSP with   lt    taglib prefix  t  tagdir   WEB-INF tags    gt    lt t product gt       lt c forEach items    cart products   var  product  gt           lt t product product    product    gt       lt  c forEach gt   lt  t product gt    That seems to me to be the very same as using an include and passing parameters to it  So are Tag Files the same as includes

User · Answer

According to   Java Revisited   Resources included by include directive are loaded during jsp translation time  while resources included by include action are loaded during request time  Any change on included resources will not be visible in case of include directive until jsp file compiles again  While in case of include action  any change in included resource will be visible in the next request  Include directive is static import  while include action is dynamic import  Include directive uses file attribute to specify resources to be included while include action uses page attribute for the same purpose

User · Answer

Main advantage of  lt jsp include   gt  over  lt    include  gt  is    lt jsp include   gt  allows to pass parameters   lt jsp include page  inclusion jsp  gt       lt jsp param name  menu  value  objectValue   gt   lt  jsp include gt    which is not possible in  lt   include file  somefile jsp    gt

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Overview of JSP Syntax Elements First  to make things more clear  here is a short overview of JSP syntax elements   Directives  These convey information regarding the JSP page as a whole  Scripting elements  These are Java coding elements such as declarations  expressions  scriptlets  and comments  Objects and scopes  JSP objects can be created either explicitly or implicitly and are accessible within a given scope  such as from anywhere in the JSP page or the session  Actions  These create objects or affect the output stream in the JSP response  or both     How content is included in JSP There are several mechanisms for reusing content in a JSP file  The following 4 mechanisms to include content in JSP can be categorized as direct reuse   for the first 3 mechanisms quoting from  quot Head First Servlets and JSP quot    1  The include directive   lt    include file  quot header html quot    gt   Static  adds the content from the value of the file  attribute to the current page at translation time   The directive was originally intended for static layout templates  like HTML  headers    2  The  lt jsp include gt  standard action   lt jsp include page  quot header jsp quot    gt   Dynamic  adds the content from the value of the  page attribute to the current page at request time  Was intended more for dynamic content  coming from JSPs  3  The  lt c import gt  JSTL tag   lt c import url    http   www example com foo bar html      gt   Dynamic  adds the content from the value of the  URL attribute to the current page  at request time   It works a lot like  lt jsp include gt   but it   s more  powerful and flexible  unlike the other two includes   the  lt c import gt  url can be from  outside the web Container  4  Preludes and codas  Static  preludes and codas can be applied only to the beginnings and ends of pages  You can implicitly include preludes  also called headers  and codas  also called footers  for a group of JSP pages by adding  lt include-prelude gt  and  lt include-coda gt  elements respectively within a  lt jsp-property-group gt  element in the Web application web xml deployment descriptor  Read more here      Configuring Implicit Includes at the Beginning and End of JSPs     Defining implicit includes   Tag File is an indirect method of content reuse  the way of encapsulating reusable content  A Tag File is a source file that contains a fragment of JSP code that is reusable as a custom tag  The PURPOSE of includes and Tag Files is different  Tag file  a concept introduced with JSP 2 0  is one of the options for creating custom tags   It s a faster and easier way to build custom tags  Custom tags  also known as tag extensions  are JSP elements that allow custom logic and output provided by other Java components to be inserted into JSP pages  The logic provided through a custom tag is implemented by a Java object known as a tag handler  Some examples of tasks that can be performed by custom tags include operating on implicit objects  processing forms  accessing databases and other enterprise services such as email and directories  and implementing flow control   Regarding your Edit Maybe in your example  in your  quot Edit quot  paragraph   there is no difference between using direct include and a Tag File  But custom tags have a rich set of features  They can  Be customized by means of attributes passed from the calling page   Pass variables back to the calling page   Access all the objects available to JSP pages   Communicate with each other  You can create and initialize a JavaBeans component  create a public EL variable that refers to that bean in one tag  and then use the bean in another tag   Be nested within one another and communicate by means of private variables    Also read this from  quot Pro JSP 2 quot   Understanding JSP Custom Tags   Useful reading   Difference between include directive and include action in JSP  JSP tricks to make templating easier  Very informative and easy to understand tutorial from coreservlet com with beautiful explanations that include  lt jsp include gt  VS   lt    include   gt  comparison table  Including Files and Applets in JSP Pages  Another nice tutorial from coreservlets com related to tag libraries and tag files  Creating Custom JSP Tag Libraries  The Basics  The official Java EE 5 Tutorial with examples  Encapsulating Reusable Content Using Tag Files   This page from the official Java EE 5 tutorial should give you even more understanding  Reusing Content in JSP Pages   This excerpt from the book  quot Pro JSP 2 quot  also discuses why do you need a Tag File instead of using static include  Reusing Content with Tag Files  Very useful guide right from the Oracle documentation  Static Includes Versus Dynamic Includes    Conclusion  Use the right tools for each task   Use Tag Files as a quick and easy way of creating custom tags that can help you encapsulate reusable content  As for the including content in JSP  quote from here     Use the include directive if the file changes rarely  It   s the fastest mechanism  If your container doesn   t automatically detect changes  you can force the changes to take effect by deleting the main page class file  Use the include action only for content that changes often  and if which page to include cannot be decided until the main page is requested

User · Answer

All three template options -  lt   include gt    lt jsp include gt  and  lt   tag gt  are valid  and all three cover different use cases   With  lt  include gt   the JSP parser in-lines the content of the included file into the JSP before compilation  similar to a C  include   You d use this option with simple  static content  for example  if you wanted to include header  footer  or navigation elements into every page in your web-app  The included content becomes part of the compiled JSP and there s no extra cost at runtime    lt jsp include gt   and JSTL s  lt c import gt   which is similar and even more powerful  are best suited to dynamic content  Use these when you need to include content from another URL  local or remote  when the resource you re including is itself dynamic  or when the included content uses variables or bean definitions that conflict with the including page   lt c import gt  also allows you to store the included text in a variable  which you can further manipulate or reuse  Both these incur an additional runtime cost for the dispatch  this is minimal  but you need to be aware that the dynamic include is not  free    Use tag files when you want to create reusable user interface components  If you have a List of Widgets  say  and you want to iterate over the Widgets and display properties of each  in a table  or in a form   you d create a tag  Tags can take arguments  using  lt   tag attribute gt  and these arguments can be either mandatory or optional - somewhat like method parameters    Tag files are a simpler  JSP-based mechanism of writing tag libraries  which  pre JSP 2 0  you had to write using Java code  It s a lot cleaner to write JSP tag files when there s a lot of rendering to do in the tag  you don t need to mix Java and HTML code as you d have to do if you wrote your tags in Java

User · Answer

Possible Duplicate Question   lt  include gt  - The directive tag instructs the JSP compiler to merge contents of the included file into the JSP before creating the generated servlet code  It is the equivalent to cutting and pasting the text from your include page right into your JSP    Only one servlet is executed at run time  Scriptlet variables declared in the parent page can be accessed in the included page  remember  they are the same page   The included page does not need to able to be compiled as a standalone JSP  It can be a code fragment or plain text  The included page will never be compiled as a standalone  The included page can also have any extension  though  jspf has become a conventionally used extension  One drawback on older containers is that changes to the include pages may not take effect until the parent page is updated  Recent versions of Tomcat will check the include pages for updates and force a recompile of the parent if they re updated  A further drawback is that since the code is inlined directly into the service method of the generated servlet  the method can grow very large  If it exceeds 64 KB  your JSP compilation will likely fail     lt jsp include gt  - The JSP Action tag on the other hand instructs the container to pause the execution of this page  go run the included page  and merge the output from that page into the output from this page    Each included page is executed as a separate servlet at run time  Pages can conditionally be included at run time  This is often useful for templating frameworks that build pages out of includes  The parent page can determine which page  if any  to include according to some run-time condition  The values of scriptlet variables need to be explicitly passed to the include page  The included page must be able to be run on its own  You are less likely to run into compilation errors due to the maximum method size being exceeded in the generated servlet class       Depending on your needs  you may either use  lt  include gt  or    lt jsp include gt

[java] What's the difference between including files with JSP include directive, JSP include action and using JSP Tag Files?

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