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The following sections provide reference information for writing JavaServer Pages (JSPs):
The following table describes the basic tags that you can use in a JSP page. Each shorthand tag has an XML equivalent.
Embeds Java source code scriptlet in your HTML page. The Java code is executed and its output is inserted in sequence with the rest of the HTML in the page. For details, see
Scriptlets on page 10-6.
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A directive can also contain name/value pair attributes in the form
attr=”value”, which provides additional instructions to the application server. See
Directives for WebLogic JSP on page 10-5.
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Declares a variable or method that can be referenced by other declarations, scriptlets, or expressions in the page. See
Declarations on page 10-6
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Defines a Java expression that is evaluated at page request time, converted to a String, and sent inline to the output stream of the JSP response. See
Expressions on page 10-7.
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Provide access to advanced features of JSP, and only use XML syntax. These actions are supported as defined in the JSP 2.0 specification. See
Actions on page 10-9.
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JSP reserves words for implicit objects in scriptlets and expressions. These implicit objects represent Java objects that provide useful methods and information for your JSP page. WebLogic JSP implements all implicit objects defined in the JSP 2.0 specification. The JSP API is described in the Javadocs available from the Sun Microsystems JSP Home Page.
| Note: | Use these implicit objects only within scriptlets or expressions. Using these keywords from a method defined in a declaration causes a translation-time compilation error because such usage causes your page to reference an undefined variable. |
request
request represents the HttpServletRequest object. It contains information about the request from the browser and has several useful methods for getting cookie, header, and session data.
response
response represents the HttpServletResponse object and several useful methods for setting the response sent back to the browser from your JSP page. Examples of these responses include cookies and other header information.
response.getWriter() method from within a JSP page; if you do, a run-time exception is thrown. Use the out keyword to send the JSP response back to the browser from within your scriptlet code whenever possible. The WebLogic Server implementation of javax.servlet.jsp.JspWriter uses javax.servlet.ServletOutputStream, which implies that you can use response.getServletOutputStream(). Keep in mind, however, that this implementation is specific to WebLogic Server. To keep your code maintainable and portable, use the out keyword.
out
out is an instance of javax.jsp.JspWriter that has several methods you can use to send output back to the browser.
JspWriter does not work. You can work around this limitation by supplying a buffered stream and then writing this stream to out. For example, the following code shows how to write an exception stack trace to out:
ByteArrayOutputStream ostr = new ByteArrayOutputStream();
exception.printStackTrace(new PrintWriter(ostr));
out.print(ostr);
pageContext
pageContext represents a javax.servlet.jsp.PageContext object. It is a convenience API for accessing various scoped namespaces and servlet-related objects, and provides wrapper methods for common servlet-related functionality.
session
session represents a javax.servlet.http.HttpSession object for the request. The session directive is set to true by default, so the session is valid by default. The JSP 2.0 specification states that if the session directive is set to false, then using the session keyword results in a fatal translation time error.
application
application represents a javax.servlet.ServletContext object. Use it to find information about the servlet engine and the servlet environment.
requestDispatcher using the ServletContext, or you can use the JSP forward directive for forwarding requests to other servlets, and the JSP include directive for including output from other servlets.
config
config represents a javax.servlet.ServletConfig object and provides access to the servlet instance initialization parameters.
page
page represents the servlet instance generated from this JSP page. It is synonymous with the Java keyword this when used in your scriptlet code.
page, you must cast it to the class type of the servlet that implements the JSP page, because it is defined as an instance of java.lang.Object. By default, the servlet class is named after the JSP filename. For convenience, we recommend that you use the Java keyword this to reference the servlet instance and get access to initialization parameters, instead of using page.
Use directives to instruct WebLogic JSP to perform certain functions or interpret the JSP page in a particular way. You can insert a directive anywhere in a JSP page. The position is generally irrelevant (except for the include directive), and you can use multiple directive tags. A directive consists of a directive type and one or more attributes of that type.
You can use either of two types of syntax: shorthand or XML:
Replace dir_type with the directive type, and dir_attr with a list of one or more directive attributes for that directive type.
There are three types of directives page, taglib, or include.
To specify a character encoding set, use the following directive at the top of the page:
<%@ page contentType="text/html; charset=custom-encoding” %>
The character set you specify with a contentType directive specifies the character set used in the JSP as well as any JSP included in that JSP.
You can specify a default character encoding by specifying it in the WebLogic-specific deployment descriptor for your Web Application.
Use a taglib directive to declare that your JSP page uses custom JSP tag extensions that are defined in a tag library. For details about writing and using custom JSP tags, see
“Programming WebLogic JSP Extensions.”
Use declarations to define variables and methods at the class-scope level of the generated JSP servlet. Declarations made between JSP tags are accessible from other declarations and scriptlets in your JSP page. For example:
<%!
int i=0;
String foo= "Hello";
private void bar() {
// ...java code here...
}
%>
Remember that class-scope objects are shared between multiple threads being executed in the same instance of a servlet. To guard against sharing violations, synchronize class scope objects. If you are not confident writing thread-safe code, you can declare your servlet as not-thread-safe by including the following directive:
<%@ page isThreadSafe="false" %>
By default, this attribute is set to true. Setting isThreadSafe to false consumes additional memory and can cause performance to degrade.
JSP scriptlets make up the Java body of your JSP servlet’s HTTP response. To include a scriptlet in your JSP page, use the shorthand or XML scriptlet tags shown here:
<%
//Your Java code goes here%>
<jsp:scriptlet>
//Your Java code goes here</jsp:scriptlet>
Note the following features of scriptlets:
out to print HTML text directly to the servlet output stream from your Java code. Call the print() method to add a string to the HTTP page response. Any time you print data that a user has previously supplied, BEA recommends that you remove any HTML special characters that a user might have entered. If you do not remove these characters, your Web site could be exploited by cross-site scripting. For more information, refer to JSP Expression Language.
To include an expression in your JSP file, use the following tag:
Replace expr with a Java expression. When the expression is evaluated, its string representation is placed inline in the HTML response page. It is shorthand for
<% out.print( expr ); %>
This technique enables you to make your HTML more readable in the JSP page. Note the use of the expression tag in the example in the next section.
Expressions are often used to return data that a user has previously supplied. Any time you print user-supplied data, BEA recommends that you remove any HTML special characters that a user might have entered. If you do not remove these characters, your Web site could be exploited by cross-site scripting. For more information, refer to JSP Expression Language.
The following example shows a JSP with HTML and embedded Java:
<html>
<head><title>Hello World Test</title></head>
<body bgcolor=#ffffff>
<center>
<h1> <font color=#DB1260> Hello World Test </font></h1>
<font color=navy>
<%
out.print("Java-generated Hello World");
%></font>
<p> This is not Java!
<p><i>Middle stuff on page</i>
<p>
<font color=navy>
<%
for (int i = 1; i<=3; i++) {
%>
<h2>This is HTML in a Java loop! <%= i %> </h2>
<%
}
%>
</font>
</center>
</body>
</html>
After the code shown here is compiled, the resulting page is displayed in a browser as follows:
You use JSP actions to modify, use, or create objects that are represented by JavaBeans. Actions use XML syntax exclusively.
The <jsp:useBean> action tag allows you to instantiate Java objects that comply with the JavaBean specification, and to refer to them from your JSP pages.
To comply with the JavaBean specification, objects need:
The <jsp:useBean> tag attempts to retrieve an existing named Java object from a specific scope and, if the existing object is not found, may attempt to instantiate a new object and associate it with the name given by the id attribute. The object is stored in a location given by the scope attribute, which determines the availability of the object. For example, the following tag attempts to retrieve a Java object of type examples.jsp.ShoppingCart from the HTTP session under the name cart.
<jsp:useBean id="cart"
class="examples.jsp.ShoppingCart" scope="session"/>
If such an object does not currently exist, the JSP attempts to create a new object, and stores it in the HTTP session under the name cart. The class should be available in the CLASSPATH used to start WebLogic Server, or in the WEB-INF/classes directory of the Web Application containing the JSP.
It is good practice to use an errorPage directive with the <jsp:useBean> tag because there are run-time exceptions that must be caught. If you do not use an errorPage directive, the class referenced in the JavaBean cannot be created, an InstantiationException is thrown, and an error message is returned to the browser.
You can use the type attribute to cast the JavaBean type to another object or interface, provided that it is a legal type cast operation within Java. If you use the attribute without the class attribute, your JavaBean object must already exist in the scope specified. If it is not legal, an InstantiationException is thrown.
The <jsp:useBean> tag syntax has another format that allows you to define a body of JSP code that is executed when the object is instantiated. The body is not executed if the named JavaBean already exists in the specified scope. This format allows you to set up certain properties when the object is first created. For example:
<jsp:useBean id="cart" class="examples.jsp.ShoppingCart"
scope=session>
Creating the shopping cart now...
<jsp:setProperty name="cart"
property="cartName" value="music">
</jsp:useBean>
| Note: | If you use the type attribute without the class attribute, a JavaBean object is never instantiated, and you should not attempt to use the tag format to include a body. Instead, use the single tag format. In this case, the JavaBean must exist in the specified scope, or an InstantiationException is thrown. Use an errorPage directive to catch the potential exception. |
After you instantiate the JavaBean object, you can refer to it by its id name in the JSP file as a Java object. You can use it within scriptlet tags and expression evaluator tags, and you can invoke its setXxx() or getXxx() methods using the <jsp:setProperty> and <jsp:getProperty> tags, respectively.
Use the scope attribute to specify the availability and life-span of the JavaBean object. The scope can be one of the following:
page
javax.servlet.jsp.PageContext of the current page. It is available only from the current invocation of this JSP page. It is not available to included JSP pages, and it is discarded upon completion of this page request.
request
request scope is used, the object is stored in the current ServletRequest, and it is available to other included JSP pages that are passed the same request object. The object is discarded when the current request is completed.
session
session scope to store the JavaBean object in the HTTP session so that it can be tracked across several HTTP pages. The reference to the JavaBean is stored in the page’s HttpSession object. Your JSP pages must be able to participate in a session to use this scope. That is, you must not have the page directive session set to false.
application
application-scope level, your JavaBean object is stored in the Web Application. Use of this scope implies that the object is available to any other servlet or JSP page running in the same Web Application in which the object is stored.
For more information about using JavaBeans, see the J SP 2.0 specification .
If you are using any type of authentication, a forwarded request made with the <jsp:forward> tag, by default, does not require the user to be re-authenticated. You can change this behavior to require authentication of a forwarded request by adding the <check-auth-on-forward/> element to the <container-descriptor> element of the WebLogic-specific deployment descriptor, weblogic.xml. For example:
<container-descriptor>
<check-auth-on-forward/>
</container-descriptor>
You can use the <jsp:include> tag to include another resource in a JSP. This tag takes two attributes:
true buffers the page output and then flushes the buffer before including the resource.
Setting flush=”false” can be useful when the <jsp:include> tag is located within another tag on the JSP page and you want the included resource to be processed by the tag.
The new JSP expression language (JSP EL) is inspired by both ECMAScript and the XPath expression languages. The JSP EL is available in attribute values for standard and custom actions and within template text. In both cases, the JSP EL is invoked consistently by way of the construct ${expr}.
The addition of the JSP EL to the JSP technology better facilitates the writing of scriptlets JSP pages. These pages can use JSP EL expressions but cannot use Java scriptlets, Java expressions, or Java declaration elements. You can enforce this usage pattern through the scripting-invalid JSP configuration element of the web.xml deployment descriptor.
For more information on the JSP expression language, see the JSP 2.0 specification.
You can use JSP EL expressions in any attribute that can accept a run-time expression, whether it is a standard action or a custom action. The following are three use cases for expressions in attribute values:
| Note: | These rules are equivalent to the JSP 2.0 conversions, except that empty strings are treated differently. |
The following two conditions must be satisfied when using JSPX:
The following shows a conditional action that uses the JSP EL to test whether a property of a bean is less than 3.
<c:if test="${bean1.a < 3}">...
</c:if>
Note that the normal JSP coercion mechanism already allows for: <mytags:if test="true" />. There may be literal values that include the character sequence ${. If this is the case, a literal with that value can be used as shown here:
<mytags:example code="an expression is ${'${'}expr}" />The resulting attribute value would then be the string an expression is ${expr}.
You can use the JSP EL directly in template text; this can be inside the body of custom or standard actions or in template text outside of any action. An exception to this use is if the body of the tag is tag dependent or if the JSP EL is turned off (usually for compatibility issues) explicitly through a directive or implicitly.
The semantics of a JSP EL expression are the same as with Java expressions: the value is computed and inserted into the current output. In cases where escaping is desired (for example, to help prevent cross-site scripting attacks), you can use the JSTL core tag <c:out>. For example:
<c:out value=”${anELexpression}” />
The following shows a custom action where two JSP EL expressions are used to access bean properties:
One value is ${bean1.a} and another is ${bean2.a.c}.
</c:wombat>
There are several implicit objects that are available to JSP EL expressions used in JSP pages. These objects are always available under these names:
pageContext
pageScope
requestScope
sessionScope
applicationScope
param
paramValues
header
headerValues
cookie
initParam
Table 10-1 shows some examples of using these implicit objects:
These sections discuss JSPEL expression literals and operators. The JSP EL syntax is pretty straightforward. Variables are accessed by name. A generalized [] operator can be used to access maps, lists, arrays of objects and properties of JavaBean objects; the operator can be nested arbitrarily. The . operator can be used as a convenient shorthand for property access when the property name follows the conventions of Java identifies. However the [] operator allows for more generalized access.
Relational comparisons are allowed using the standard Java relational operators. Comparisons may be made against other values, or against boolean (for equality comparisons only), String, integer, or floating point literals. Arithmetic operators can be used to compute integer and floating point values. Logical operators are available.
Literals exist for boolean, integer, floating point, string, null.
JSP pages are mostly used in presentation, and in that usage, experience suggests that it is most important to be able to provide as good a presentation as possible, even when there are simple errors in the page. To meet this requirement, the JSP EL does not provide warnings, just default values and errors. Default values are typecorrect values that are assigned to a subexpression when there is some problem. An error is an exception thrown (to be handled by the standard JSP machinery).
The following is a list of operators provided by the JSP expression language:
For more information about the operators and their functions, see the JSP 2.0 specification.
The following is operator precedence, from highest to lowest, left-to-right.
The following words are reserved for the language and should not be used as identifiers.
Note that many of these words are not in the language now, but they may be in the future, so developers should avoid using these words now.
A core concept in the JSP EL is the evaluation of a variable name into an object. The JSP EL API provides a generalized mechanism, a VariableResolver, that will resolve names into objects. The default resolver is what is used in the evaluation of JSP EL expressions in template and attributes. This default resolver provides the implicit objects discussed in JSP Expression Language Implicit Objects.
The default resolver also provides a map for other identifiers by looking up its value as an attribute, according to the behavior of PageContext.findAttribute(String) on the pageContext object. For example: ${product}.
This expression looks for the attribute named product, searching the page, request, session, and application scopes, and returns its value. If the attribute is not found, null is returned. See chapter 14, “Expression Language API,” of the JSP 2.0 specification. for further details on the VariableResolver and how it fits with the evaluation API.
Expressions and scriptlets enable a JSP to receive data from a user and return the user supplied data. For example, the sample JSP in Listing 10-1 prompts a user to enter a string, assigns the string to a parameter named userInput, and then uses the <%= javax.servlet.ServletRequest.getParameter("userInput")%> expression to return the data to the browser.
<html>
<body>
<h1>My Sample JSP</h1>
<form method="GET" action="mysample.jsp">
Enter string here:
<input type="text" name="userInput" size=50>
<input type=submit value="Submit">
</form>
<br>
<hr>
<br>
Output from last command:
<%=javax.servlet.ServletRequest.getParameter("userInput")%>
</body>
</html>
This ability to return user-supplied data can present a security vulnerability called cross-site scripting, which can be exploited to steal a user’s security authorization. For a detailed description of cross-site scripting, refer to “Understanding Malicious Content Mitigation for Web Developers” (a CERT security advisory) at http://www.cert.org/tech_tips/malicious_code_mitigation.html.
To remove the security vulnerability, before you return data that a user has supplied, scan the data for any of the HTML special characters in Table 10-2. If you find any special characters, replace them with their HTML entity or character reference. Replacing the characters prevents the browser from executing the user-supplied data as HTML.
WebLogic Server provides the weblogic.servlet.security.Utils.encodeXSS() method to replace the special characters in user-supplied data. To use this method, provide the user-supplied data as input. For example,<%= weblogic.servlet.security.Utils.encodeXSS(
javax.servlet.ServletRequest.getParameter("userInput"))%>
To secure an entire application, you must use the encodeXSS() method each time you return user-supplied data. While the previous example is an obvious location in which to use the encodeXSS() method, Table 10-3 describes other locations to consider using the encodeXSS() method.
Sessions in WebLogic JSP perform according to the JSP 2.0 specification. The following suggestions pertain to using sessions:
ClassCastException errors.
Using the JSP provides a convenient way to include the Java Plug-in in a Web page, by generating HTML that contains the appropriate client browser tag. The Java Plug-in allows you to use a Java Runtime Environment (JRE) supplied by Sun Microsystems instead of the JVM implemented by the client Web browser. This feature avoids incompatibility problems between your applets and specific types of Web browsers. The Java Plug-in is available from Sun at http://java.sun.com/products/plugin/.
Because the syntax used by Internet Explorer and Netscape is different, the servlet code generated from the <jsp:plugin> action dynamically senses the type of browser client and sends the appropriate <OBJECT> or <EMBED> tags in the HTML page.
The <jsp:plugin> tag uses many attributes similar to those of the <APPLET> tag, and some other attributes that allow you to configure the version of the Java Plug-in to be used. If the applet communicates with the server, the JVM running your applet code must be compatible with the JVM running WebLogic Server.
In the following example, the plug-in action is used to deploy an applet:
<jsp:plugin type="applet" code="examples.applets.PhoneBook1"
codebase="/classes/" height="800" width="500"
jreversion="2.0"
nspluginurl=
"http://java.sun.com/products/plugin/1.1.3/plugin-install.html"
iepluginurl=
"http://java.sun.com/products/plugin/1.1.3/
jinstall-113-win32.cab#Version=1,1,3,0" >
<jsp:params>
<param name="weblogic_url" value="t3://localhost:7001">
<param name="poolname" value="demoPool">
</jsp:params>
<jsp:fallback>
<font color=#FF0000>Sorry, cannot run java applet!!</font>
</jsp:fallback>
</jsp:plugin>
The sample JSP syntax shown here instructs the browser to download the Java Plug-in version 1.3.1 (if it has not been downloaded previously), and run the applet identified by the code attribute from the location specified by codebase.
The jreversion attribute identifies the spec version of the Java Plug-in that the applet requires to operate. The Web browser attempts to use this version of the Java Plug-in. If the plug-in is not already installed on the browser, the nspluginurl and iepluginurl attributes specify URLs where the Java Plug-in can be downloaded from the Sun Web site. Once the plug-in is installed on the Web browser, it is not downloaded again.
Because WebLogic Server uses the Java 1.3.x VM, you must specify the Java Plug-in version 1.3.x in the <jsp:plugin> tag. To specify the 1.3 JVM in the previous example code, replace the corresponding attribute values with the following:
jreversion="1.3"
nspluginurl=
"http://java.sun.com/products/plugin/1.3/plugin-install.html"
iepluginurl=
"http://java.sun.com/products/plugin/1.3/jinstall-131-win32.cab"
The other attributes of the plug-in action correspond with those of the <APPLET> tag. You specify applet parameters within a pair of <params> tags, nested within the <jsp:plugin> and </jsp:plugin> tags.
The <jsp:fallback> tags allow you to substitute HTML for browsers that are not supported by the <jsp:plugin> action. The HTML nested between the <fallback> and </jsp:fallback> tags is sent instead of the plug-in syntax.
The WebLogic JSP compiler is deprecated. BEA recommends that you use the WebLogic appc compiler, weblogic.appc, to compile EAR files, WAR files and EJBs.
For better compilation performance, the WebLogic JSP compiler transforms a JSP directly into a class file on the disk instead of first creating a java file on the disk and then compiling it into a class file. The java file only resides in memory.
To see the generated java file, turn on the -keepgenerated flag which dumps the in-memory java file to the disk.
| Note: | During JSP compilation, neither the command line flag (compilerclass) nor the descriptor element is invoked. |
The JSP compiler works in much the same way that other WebLogic compilers work (including the RMI and EJB compilers). To start the JSP compiler, enter the following command.
$ java weblogic.jspc -options fileName
Replace fileName with the name of the JSP file that you want to compile. You can specify any options before or after the target fileName. The following example uses the -d option to compile myFile.jsp into the destination directory, weblogic/classes:
$ java weblogic.jspc -d /weblogic/classes myFile.jsp
| Note: | If you are precompiling JSPs that are part of a Web Application and that reference resources in the Web Application (such as a JSP tag library), you must use the -webapp flag to specify the location of the Web Application. The -webapp flag is described in the following listing of JSP compiler options. |
Use any combination of the following options:
-classpath
CLASSPATH. Include directories containing any classes required by the JSP. For example (to be entered on one line):
$ java weblogic.jspc
-classpath java/classes.zip;/weblogic/classes.zip
myFile.JSP
-charsetMap
contentType directives to java charset names. For example:
-charsetMap x-sjis=Shift_JIS,x-big5=Big5
-commentary
-compileAll
-webapp flag. (See the listing for -webapp in this list of options.). JSPs in subdirectories are also compiled.
-compileFlags
java weblogic.jspc -compileFlags "-g -v" myFile.jsp
-compiler
javac. The Java compiler program should be in your PATH unless you specify the absolute path to the compiler explicitly.
-compilerclass
-d <dir>
CLASSPATH.
-depend
-debug
-deprecation
-docroot directory
-encoding default|named character encoding
default which specifies using the default character encoding of your JDK, (b) a named character encoding, such as 8859_1. If the -encoding flag is not specified, an array of bytes is used.
-g
-help
-J
-k
-keepgenerated
-noTryBlocks
java.lang.VerifyError exception when compiling, use this flag to allow the JSPs to compile correctly.
-nowarn
-noPrintNulls
-O
-g flag.
-package packageName
jsp_servlet.
-superclass classname
HttpServlet or GenericServlet.
-verbose
verbose flag to the Java compiler specified with the compiler flag. See the compiler documentation for more information. The default is off.
-verboseJavac
-version
-webapp directory
You can configure WebLogic Server to precompile your JSPs when a Web Application is deployed or re-deployed or when WebLogic Server starts up by setting the precompile parameter to true in the <jsp-descriptor> element of the weblogic.xml deployment descriptor. To avoid recompiling your JSPs each time the server restarts and when you target additional servers, precompile them using weblogic.jspc and place them in the WEB-INF/classes folder and archive them in a .war file. Keeping your source files in a separate directory from the archived .war file will eliminate the possibility of errors caused by a JSP having a dependency on one of the class files.
Another way to prevent your JSPs from recompiling is to use the JSPClassServlet in place of JSPServlet and to place your precompiled JSPs into the WEB-INF/classes directory. This will remove any possibility of the JSPs being recompiled, as the server will not look at the source code. The server will not note any changes to the JSPs and recompile them if you choose this option. This option allows you to completely remove the JSP source code from your application after precompiling.
This is an example of how to add the JSPClassServlet to your Web Application’s web.xml file.
<servlet-name>JSPClassServlet</servlet-name>
<servlet-class>weblogic.servlet.JSPClassServlet</servlet-class>
<servlet-name>JSPClassServlet</servlet-name>
<url-pattern>*.jsp</url-pattern>
As when using virtual hosting, you must have physical directories that correspond to the mappings you create to allow your files to be found by the server.
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