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Here are some of my notes from HTML, Servlets, JSP Course:
ServletsgetPathInfo() - path in URL getPathTranslated() - where the filename is located
Setting the header
response.setHeader("Content-type","es");
utility native2ascii - converts native codepage to UTF-8 encoding. Useful for .property files and localization
Global attributes
this.getServletContext().setAttributes("name", value);
- attribute that is visible in the whole application.. for more servlets
JSP<%-- comment
<%! - declaration (it stores the code out of the service method)
<%@ - directive (affects translation of JSP to Servlet, compilation.. useful for tuning for specific cases like setting the error page, code page imports, etc.)
XML syntax of JSP page:
... - same as <%!
include<%@ include file='file.jsp" %>
includes file to a page (before translation)
- don't recognize if the included file has changed
- includes all of the parameters or attributes for included page
or
< jsp:include page="file.jsp" >
dynamic include (during the processing of main page), more flexible
- this way we can include result of server or other JSP page
- explicit parameter passing to included page by < jsp: param name="name_of_parameter" value="value_of_parameter"> tag.
for included pages, there is a need for inserting pages without HTML < body > types !
The page directive
<%@ page ... % >
useful for setting additional properties for jsp page like isErrorPage="true|false"
pluginsusage:
< jsp:plugin >
...
< /jsp:plugin >
it inserts Java applet to the page
System environmentsusage:
TERM=vt100
java -D user.term=$TERM
then, we can access this environment variable by:
System.getProperties() - it returns instance of class Property.
System.getProperties().getProperty("user.term");
System.getProperties().remove("user.term");JavaBeansrequirements for JavaBeans:
- there have to be set/get methods specified
- has to have public default constructor (without parameters)
- it should be in a package
- serializable
- get/set methods has to have the same data type!
- bean cannot modify content of a page!
... in general, JavaBean is a standard Class.
It can be used as a simple component in a JSP page.
- get method has to be fast, and it should be plain and simple.
usage in a JSP page:
< jsp:useBean id="nameOfBean" scope="session" class="myPackage.Counter" />
< jsp:getProperty name="nameOfBean" property="myCount" />
this is the same as
<%= Counter.myCount %>
with JSTL Expression language:
< c:out value="${Counter.myCount}" >
automatically set the bean attributes from from names (!important!):
< jsp:setProperty name="pocetMiest" property="*" />
scope can be:
application - the bean is available in all application, when that's in more JSP pages, one of them can create it once and other JSP pages can use it. It's something like a global object for all application.
session - stored data, just for this session
request - just for request or forward
page - smallest scope, just on a page that is called (forwarded or included)
Custom Tags
- reusability
- components which you can download and use on your JSP page (3rd party)
- Custom tags can also command the pageflow instead of JavaBean, you can for example terminate a page by some custom tag.
eg. mytaglib.tld - containts a descriptor of tags in XML
usage:
< %@ taglib uri="/WEB-INF/jsp/mytaglib.tld" prefix="first" % >
some text ....
or
< %@ taglib uri="mytaglib" prefix="first" % > -> mytablib has to be defined in web.xml
- advantage: when changing a tag library, it can be changed only in web.xml instead of changing it manually in every file.
< first: something />
some text ....
< first:something name="myAttribute" value="myValue" / > -> has to be defined in mytaglib.tld !
in tld file:
- < rtexprvalue >true|false< /rtexprvalue > - says that we can use in params < %= expression % >
eg.:
< first:something name="myAttribute" value="< %= expression % >" / >writing Custom tag class:
- imports javax.servlet.jsp.tagext.*;
- class has to implement class Tag or has to extend TagSupport class
method doStartTag() - method that is executed when there is a occurency of a start tag.
pageContext.getOut.print("I will print this"); // in try/catch block
method doEndTag() - method is executed when there is a closing tag.
method getParent() - returns a parent of a current tag;
method release() - there we can release some system resources, etc.
when there is a body of a tag, it has to implement BodyTagSupport instead of simple TagSupport
it means, that you can nest multiple tags within the tag content.
method doAfterBody() - for handling nested content
BodyContent bc = getBodyContent(); // content of a tag body
String body = bc.getString(); // convertion to a String
JSPWriter out = bc.getEnclosingWriter(); // enclosing writer of the parent tag.. result can will be written there.
possible return values on the end of a tag handling method :
return SKIP_BODY; (ignores the body of a custom tag in JSP) - skip to handling method doEndTag()
return SKIP_PAGE; - skips the entire following content of a page.
return EVAL_BODY_TAG; - evaluates the body of a tag
return EVAL_PAGE; - we can continue in page evaluation
JSTL (Java Standard Tag Libraries)- useful tags for creating cycles, we can elliminate scriptlets,
- formating messages
- internalization
- database communication
- expression language
expression language- eases the manipulation with JavaBeans: eg. ${beanName.propertyName}
- allow you to evaluate given expression: eg. ${3+5}
- ${param["foo"]} - HTML parameters from query string
- ${cookie["myName"]} - cookie with name myName
JavaServer faces- UI components for HTML
- saving it's state between calls
- we can work with beans on a server
- component model for HTML
- quite new technology
- implements MVC(model / view / controller) pattern as known as Model 2
Sending e-mail
package sun.netsmtp.SmtpClient;
SmtpClient smtp = new SmtpClient("...IP..");
smtp.from(from);
smtp.to(to);
PrintStream msg = smtp.startMesage();
msg.println(....);
smtp.closeServer();
- attachments cannot be inserted
JavaMail API- more complex
- XSD is exchange for DTD
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