Web Applications with Java/JSP

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Java Server Pages

Java Server Pages (JSPs) is a technology for dynamic content generation for things like Web pages. JSPs are analogous to PHP pages, where static text can be mixed with Java code, and the result is sent to the client. Technically speaking, JSPs are translated on the fly by a special servlet (provided by the Servlet Container) into their own servlets and compiled into bytecode, and then run just like “normal” servlets. Listing 4 shows the code for tasks.jsp—the page referenced in GetTasksServlet's doGet() method above.

The page begins with a page declaration that includes some metadata about the page, including the output character encoding, and then some “taglib” tags that tell the JSP compiler I want to use some “tag libraries”. Tag libraries are helper libraries that allow JSP scripts to wield powerful tools using very simple syntax. After the DOCTYPE, there is a <fmt:setBundle> element, and in the <title> of the page, there is a <fmt:message> element. These two tags, defined by the “fmt” tag library, work together to provide internationalization capabilities to this page. The <fmt:setBundle> tag defines the string resource bundle to be used by the page, and the <fmt:message> tag uses that bundle to pull localized text from the appropriate file to display in the page. The result is, when I visit this page with my Web browser set to the en_US locale, I get text in English, but if I switch the locale to fr_BE and reload the page, the page will switch into French without any further programming.

The standard Java API actually provides all this capability out of the box, but the JSTL (Java Standard Template Library) “fmt” tag library gives us access to Java's internationalization APIs without having to write any Java code. By providing a Java property file (a text file with simple key=value syntax) for each locale I want to support, I get text localization practically for free. Further down in the JSP file, you can see the use of another “fmt” tag, <fmt:formatDate>. This tag formats a date object using the user's locale and a simple name for the format (“simple” in this case). This results in MM/dd/yy in the US and dd/MM/yy in Belgium.

The next JSTL tag is <c:forEach>. This tag actually encloses a body, which is evaluated multiple times: once for each item it finds in the “items” attribute. The value of ${items} means that the value is not just a simple literal value, but an expression that should be evaluated. The object “items” is found in the request object's “attributes”—remember I put it there in the servlet code—and used here as the data for the loop. Within the body of <c:forEach>, the “item” object is defined and can be used by any JSTL tags.

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Comments

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Helpful article.

Raymond's picture

Thank you for bringing greater clarity to the Java Web world.

Cool article! Very insghtful.

Barbara's picture

This is an insightful article that expands horizons for Java users!

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