 What are the life-cycle methods of .html?
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A: Life-cycle methods of the.html are:
a).htmlInit(): The container calls the.htmlInit() to initialize the servlet instance. It is called before any other method, and is called only once for a servlet instance.
b).htmlService(): The container calls the .htmlservice() for each request and it passes the request and the response objects. .htmlService() method cann't be overridden.
c).htmlDestroy(): The container calls this when its instance is about to destroyed.
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What is a Expression?
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A: An expression tag contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the.html file. Because the value of an expression is converted to a String, you can use an expression within text in a.html file. Like You cannot use a semicolon to end an expression. Expression tag is used to insert Java values directly into the output. Syntax for the Expression tag is: <%= expression %> An expression tag contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the.html file. The following expression tag displays time on the output: <%=new java.util.Date()%>
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What is a Declaration?
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A: A declaration declares one or more variables or methods for use later in the.html source file. A declaration must contain at least one complete declarative statement. You can declare any number of variables or methods within one declaration tag, as long as they are separated by semicolons. The declaration must be valid in the scripting language used in the.html file.
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What is a Scriptlet?
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A: A scriptlet can contain any number of language statements, variable or method declarations, or expressions that are valid in the page scripting language.Within scriptlet tags, you can 1.Declare variables or methods to use later in the file (see also Declaration). 2.Write expressions valid in the page scripting language (see also Expression). 3.Use any of the.html implicit objects or any object declared with a .html:useBean> tag. You must write plain text, HTML-encoded text, or other.html tags outside the scriptlet. Scriptlets are executed at request time, when the.html engine processes the client request. If the scriptlet produces output, the output is stored in the out object, from which you can display it.
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What are implicit objects? List them?
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A: Certain objects that are available for the use in.html documents without being declared first. These objects are parsed by the.html engine and inserted into the generated servlet. The implicit objects re listed below request response pageContext session application out config page exception
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Difference between forward and sendRedirect?
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A: The <.html:forward> element forwards the request object containing the client request information from one.html file to another file. The target file can be an HTML file, another.html file, or a servlet, as long as it is in the same application context as the forwarding.html file. sendRedirect sends HTTP temporary redirect response to the browser, and browser creates a new request to go the redirected page. The response.sendRedirect kills the session variables. When you invoke a forward request, the request is sent to another resource on the server, without the client being informed that a different resource is going to process the request. This process occurs completly with in the web container. When a sendRedirtect method is invoked, it causes the web container to return to the browser indicating that a new URL should be requested. Because the browser issues a completly new request any object that are stored as request attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward.
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What is the difference between <.html:include page = ... > and <%@ include file = ... >?
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A: Both the tag includes the information from one page in another. The differences are as follows: <.html:include page = ... >: This is like a function call from one.html to another.html. It is executed ( the included page is executed and the generated html content is included in the content of calling.html) each time the client page is accessed by the client. This approach is useful to for modularizing the web application. If the included file changed then the new content will be included in the output. <%@ include file = ... >: In this case the content of the included file is textually embedded in the page that have
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How does.html handle run-time exceptions?
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A: You can use the errorPage attribute of the page directive to have uncaught run-time exceptions automatically forwarded to an error processing page. For example: redirects the browser to the.html page error.html if an uncaught exception is encountered during request processing. Within error.html, if you indicate that it is an error-processing page, via the directive: Throwable object describing the exception may be accessed within the error page via the exception implicit object. Note: You must always use a relative URL as the value for the errorPage attribute.
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What is.html Output Comments?
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A: .html Output Comments are the comments that can be viewed in the HTML source file. Example: <!-- This file displays the user login screen --> and <!-- This page was loaded on <%= (new java.util.Date()).toLocaleString() %> --> A comment that is sent to the client in the viewable page source.The.html engine handles an output comment as uninterpreted HTML text, returning the comment in the HTML output sent to the client. You can see the comment by viewing the page source from your Web browser. JSP Syntax Example 1 Displays in the page source:
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How can I implement a thread-safe.html page? What are the advantages and Disadvantages of using it?
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A: You can make your.htmls thread-safe by having them implement the SingleThreadModel interface. This is done by adding the directive within your.html page. With this, instead of a single instance of the servlet generated for your.html page loaded in memory, you will have N instances of the servlet loaded and initialized, with the service method of each instance effectively synchronized. You can typically control the number of instances (N) that are instantiated for all servlets implementing SingleThreadModel through the admin screen for your.html engine. More importantly, avoid using the tag for variables. If you do use this tag, then you should set isThreadSafe to true, as mentioned above. Otherwise, all requests to that page will access those variables, causing a nasty race condition. SingleThreadModel is not recommended for normal use. There are many pitfalls, including the example above of not being able to use . You should try really hard to make them thread-safe the old fashioned way: by making them thread-safe .
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How do I use a scriptlet to initialize a newly instantiated bean?
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A: A.html:useBean action may optionally have a body. If the body is specified, its contents will be automatically invoked when the specified bean is instantiated. Typically, the body will contain scriptlets or.html:setProperty tags to initialize the newly instantiated bean, although you are not restricted to using those alone. The following example shows the 'today' property of the Foo bean initialized to the current date when it is instantiated. Note that here, we make use of a.html expression within the.html:setProperty action. .html:useBean id="foo" class="com.Bar.Foo" > .html:setProperty name="foo" property="today" value="" / > <.html:useBean >
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What is a Hidden Comment?
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A: A comments that documents the.html page but is not sent to the client. The.html engine ignores a hidden comment, and does not process any code within hidden comment tags. A hidden comment is not sent to the client, either in the displayed.html page or the HTML page source. The hidden comment is useful when you want to hide or "comment out" part of your.html page. You can use any characters in the body of the comment except the closing --%> combination. If you need to use --%> in your comment, you can escape it by typing --%\>. JSP Syntax <%-- comment --%> Examples <%@ page language="java" %> <html> <head><title>A Hidden Comment </title></head> <body> <%-- This comment will not be visible to the colent in the page source --%> </body> </html>
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How can I prevent the word "null" from appearing in my HTML input text fields when I populate them with a resultset that has null values?
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A: You could make a simple wrapper function, like String blanknull(String s) { return (s == null) ?"":s; } then use it inside your.html form, like <input type="text" name="lastName" value="<%=blanknull(lastName)%>" >
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What's a better approach for enabling thread-safe servlets and.htmls? SingleThreadModel Interface or Synchronization?
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A: Although the SingleThreadModel technique is easy to use, and works well for low volume sites, it does not scale well. If you anticipate your users to increase in the future, you may be better off implementing explicit synchronization for your shared data. The key however, is to effectively minimize the amount of code that is synchronzied so that you take maximum advantage of multithreading. Also, note that SingleThreadModel is pretty resource intensive from the server\'s perspective. The most serious issue however is when the number of concurrent requests exhaust the servlet instance pool. In that case, all the unserviced requests are queued until something becomes free - which results in poor performance. Since the usage is non-deterministic, it may not help much even if you did add more memory and increased the size of the instance pool.
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How can I enable session tracking for.html pages if the browser has disabled cookies?
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A: We know that session tracking uses cookies by default to associate a session identifier with a unique user. If the browser does not support cookies, or if cookies are disabled, you can still enable session tracking using URL rewriting. URL rewriting essentially includes the session ID within the link itself as a name/value pair. However, for this to be effective, you need to append the session ID for each and every link that is part of your servlet response. Adding the session ID to a link is greatly simplified by means of of a couple of methods: response.encodeURL() associates a session ID with a given URL, and if you are using redirection, response.encodeRedirectURL() can be used by giving the redirected URL as input. Both encodeURL() and encodeRedirectedURL() first determine whether cookies are supported by the browser; if so, the input URL is returned unchanged since the session ID will be persisted as a cookie. Consider the following example, in which two.html files, say hello1.html and hello2.html, interact with each other. Basically, we create a new session within hello1.html and place an object within this session. The user can then traverse to hello2.html by clicking on the link present within the page. Within hello2.html, we simply extract the object that was earlier placed in the session and display its contents. Notice that we invoke the encodeURL() within hello1.html on the link used to invoke hello2.html; if cookies are disabled, the session ID is automatically appended to the URL, allowing hello2.html to still retrieve the session object. Try this example first with cookies enabled. Then disable cookie support, restart the brower, and try again. Each time you should see the maintenance of the session across pages. Do note that to get this example to work with cookies disabled at the browser, your.html engine has to support URL rewriting. hello1.html <%@ page session=\"true\" %> <% Integer num = new Integer(100); session.putValue("num",num); String url =response.encodeURL("hello2.html"); %> <a href=\'<%=url%>\'>hello2.html</a> hello2.html <%@ page session="true" %> <% Integer i= (Integer )session.getValue("num"); out.println("Num value in session is " + i.intValue()); %>
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What is the difference b/w variable declared inside a declaration part and variable declared in scriplet part?
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A: Variable declared inside declaration part is treated as a global variable.that means after convertion.html file into servlet that variable will be in outside of service method or it will be declared as instance variable.And the scope is available to complete.html and to complete in the converted servlet class.where as if u declare a variable inside a scriplet that variable will be declared inside a service method and the scope is with in the service method.
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Is there a way to execute a.html from the comandline or from my own application?
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A: There is a little tool called.htmlExecutor that allows you to do just that. The developers (Hendrik Schreiber & Peter Rossbach ) aim was not to write a full blown servlet engine, but to provide means to use.html for generating source code or reports. Therefore most HTTP-specific features (headers, sessions, etc) are not implemented, i.e. no reponseline or header is generated. Nevertheless you can use it to precompile.html for your website.
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