Teach Yourself J2EE in 21 Days phần 8 pot

14: <TR><TD><xsl:value-of select=”name()”/>:</TD> ➥<TD><xsl:value-of select=”.”/></TD></TR> 15: </xsl:template> 16: </xsl:stylesheet> Listing 17.11 brings together several features of stylesheets that have been described pre- viously. The rule at line 3 matches a <job> element, and the customer and reference attributes are inserted into the output at line 4. At line 5, the job description child ele- ment is output in its own paragraph, and the skill and location children are output inside an HTML table at lines 6 and 8. In line 6, the HTML table border attribute is enclosed in quotes so that it is valid XML (the same is also true for line 10 and the colspan attribute). Line 12 uses one rule to match the <location> or <skill> elements. Finally, the name of the selected node is inserted into the output stream using the name() function in line 13. Figure 17.2 shows the result of applying the table.xsl stylesheet from Listing 17.10 to the jobs.xml file. 766 Day 17 LISTING 17.11 Continued FIGURE 17.2 The XML to HTML table transformation. XSL supports significantly more complex transformation rules than those shown so far. The next section will provide an overview of some of the additional XSL features. 21 0672323842 CH17 3/20/02 9:32 AM Page 766 Transforming XML Documents 767 17 Using Stylesheet Elements XSL defines about twenty elements for transforming XML documents. So far, you have seen the basic <xsl:template> element for defining template rules and the <xsl:apply- templates> and <xsl:value-of> rules for including data in the output document. Many transformations can be defined just using these three elements. However, some of the more complex requirements need additional support from XSL. Processing Whitespace and Text By default, an XSL transformation retains the whitespace in the original document. This may not be required for the following reasons: • The whitespace is generally ignored when processing the output. • Users browsing the transformed document may find the whitespace misleading or annoying. • Some output document formats may be whitespace sensitive, so the transformation must control the way whitespace is written to the output. The <xsl:strip-space> tag can be used to strip leading and trailing whitespace from an element’s body. The tag takes an elements attribute that defines from which elements to strip the whitespace. Elements are selected using the XPath notation. Listing 17.12 shows the simple.xsl stylesheet shown in Listing 17.2 enhanced to strip whitespace from all elements. LISTING 17.12 Full Text of simpleStrip.xsl 1: <?xml version=”1.0”?> 2: <xsl:stylesheet version=”1.0” ➥xmlns:xsl=”http://www.w3.org/1999/XSL/Transform”> 3: <xsl:strip-space elements=”*”/> 4: </xsl:stylesheet> Applying this stylesheet to the jobs.xml document produces the following output: LondonMust like to talk and smokeCigar makerCriticWashingtonMust ➥be honestTree surgeon No whitespace has been included but, as you can see, this is not particularly readable because the whitespace between the elements has been lost. You could selectively strip whitespace from elements using tags, as shown in the following: <xsl:strip-space elements=”jobSummary|job”/> But this will still retain multiple spaces in the non-stripped elements. 21 0672323842 CH17 3/20/02 9:32 AM Page 767 Inserting whitespace into the output stream is best done using the <xsl:text> element. Any whitespace inside the <xsl:text> element is retained. You could rewrite the default rule for all elements to include a single blank line before each element, as shown in Listing 17.13. LISTING 17.13 Full Text of simpleSpace.xsl 1: <?xml version=”1.0”?> 2: <xsl:stylesheet version=”1.0” ➥xmlns:xsl=”http://www.w3.org/1999/XSL/Transform”> 3: <xsl:strip-space elements=”*”/> 4: <xsl:template match=”*”> 5: <xsl:text> 6: </xsl:text> 7: <xsl:apply-templates/> 8: </xsl:template> 9: </xsl:stylesheet> The blank line is inserted at lines 5 and 6. Notice how the closing </xsl:text> tag is not indented; otherwise, additional whitespace would have been included. You could not use an empty tag here (<xsl:text/>) because you need to insert the end of line into the out- put document). The output from applying this stylesheet to jobs.xml is as follows: <?xml version=”1.0” encoding=”UTF-8”?> London Must like to talk and smoke Cigar maker Critic Washington Must be honest Tree surgeon Whitespace is automatically stripped from the stylesheet, which is why the indented <xsl:apply-templates/> tag does not insert any whitespace before the output text. The <xsl:text> tag is also used to insert text containing XML special characters (such as < and &) into the output stream. These characters are defined in the stylesheet using their character reference form (such as &lt;) and are output in the same format. Wrapping the symbols inside an <xsl:text> element with the disable-output- escaping attribute set to yes will output any special symbols as simple Unicode charac- ters. The <xsl:text> element is most often used when the output document is not an XML document, or the output is not well formed XML. 768 Day 17 21 0672323842 CH17 3/20/02 9:32 AM Page 768 Transforming XML Documents 769 17 The following example shows one way of inserting a piece of JavaScript into your Web page (using comments, as described in the “Adding Comments” section later in this chapter, is a better approach): <xsl:template match=”SCRIPT”> <SCRIPT language=”javascript”> <xsl:text disable-output-escaping=”yes”> &lt;! if (n &lt; 0 &amp;&amp; m &gt; 0) { n = m; } // &gt; </xsl:text> </SCRIPT> </xsl:template> This transforms to <SCRIPT language=”javascript”> <! if (n < 0 && m > 0) { n = m; } // > </SCRIPT> Adding Comments You can add a comment to a stylesheet as follows: <xsl:template match=”job”> <! this is a job definition > <xsl:apply-templates/> </xsl:template> Using XML comments in this way is treated as a stylesheet comment and is not inserted into the output stream. To include a comment in the output document, you must use the <xsl:comment> element, as shown in the following: <xsl:template match=”job”> <xsl:comment>this is a job definition</xsl:comment> <xsl:apply-templates/> </xsl:template> Disabling the output escaping mechanism is dangerous and should only be used when no alternative solution can be found. The disable-output- escaping attribute is often abused, much like the goto statement in some programming languages. Caution 21 0672323842 CH17 3/20/02 9:32 AM Page 769 The following example shows a better solution to inserting JavaScript in an HTML page: <xsl:template match=”SCRIPT”> <SCRIPT language=”javascript”> <xsl:text> <xsl:comment> if (n &lt; 0 &amp;&amp; m &gt; 0) { n = m; } // </xsl:comment> </xsl:text> </SCRIPT> </xsl:template> Another advantage of using <xsl:comment> is that the actual comment can be derived from data in the source XML document. The following example inserts the job customer and reference attributes into a comment: <xsl:template match=”job”> <xsl:comment>Job definition for <xsl:value-of select=”@customer”/>/ ➥<xsl:value-of select=”@reference”/></xsl:comment> <xsl:apply-templates/> </xsl:template> Finally, if you want to copy the comments from the original XML document into the transformed document, add the following rule to your stylesheet: <xsl:template match=”comment()”> <xsl:comment><xsl:value-of select=”.”/></xsl:comment> </xsl:template> Attribute Values Some transformations require output element attributes to vary according to the element being processed. As a simple example, think back to Day 16 when you first looked at XML and the simple structure for the job summary, as shown in the following: <?xml version=”1.0”?> <jobSummary> <job> <customer>winston</customer> <reference>Cigar Trimmer</reference> <location>London</location> <description>Must like to talk and smoke</description> <! skills list for winston > <skill>Cigar maker</skill> <skill>Critic</skill> </job> </jobSummary> This version didn’t use attributes to represent the primary key of the job. Imagine that you have to convert this form of document into the new form using attributes. Your first attempt to do this might be as follows: 770 Day 17 21 0672323842 CH17 3/20/02 9:32 AM Page 770 Transforming XML Documents 771 17 <xsl:template match=”job”> <job customer=”<xsl:value-of select=’./customer’/>” job=”<xsl:value-of select=’./reference’/>” /> <xsl:apply-templates/> </xsl:template> Unfortunately, this won’t work, because XML does not allow you to define elements inside attributes of other elements. You can always insert a < symbol inside an attribute value using &lt; but this would not be interpreted as an element. To get around the XML restriction of not allowing elements to be defined inside attribut- es, XSLT stylesheets let you insert the value of elements inside attributes by enclosing the XPath name in braces, as shown in the following: <xsl:template match=”job”> <job customer=”{./customer}” job=”{./reference}” /> <xsl:apply-templates select=’location|description|skill’/> </xsl:template> To prevent the nested <customer> and <reference> elements from being output by the default template rules, the <apply-templates> element selects the required child ele- ments of the job element. An alternative syntax that excludes the unwanted elements and doesn’t need you to explicitly list the required elements uses an XPATH expression nota- tion that has not been discussed today. For completeness, this rule it is as follows: <xsl:apply-templates select=”./*[name()!=’customer’ and name()!=’reference’]”/> If you want to convert the new style job element (with attributes) back to the one with nested elements, you use the following rule: <xsl:template match=”job”> <job> <customer><xsl:value-of select=”@customer/></customer> <reference><xsl:value-of select=”@reference/></reference> <xsl:apply-templates/> </job> </xsl:template> Creating and Copying Elements In the previous section, you learned how to convert one XML document to another by con- verting nested elements into tags. But what do you do if you want to convert an attribute into an element where the attribute value is the name of the element, or vice versa? As a simple example, consider a Deployment Descriptor (DD) for two Session beans, as shown in Listing 17.14. 21 0672323842 CH17 3/20/02 9:32 AM Page 771 LISTING 17.14 Full Text of dd.xml 1: <?xml version=”1.0” encoding=”UTF-8”?> 2: <! DOCTYPE ejb-jar PUBLIC ➥’-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN’ ➥’http://java.sun.com/dtd/ejb-jar_2_0.dtd’ > 3: <ejb-jar> 4: <display-name>Agency</display-name> 5: <enterprise-beans> 6: <session> 7: <display-name>AgencyBean</display-name> 8: <ejb-name>AgencyBean</ejb-name> 9: <home>agency.AgencyHome</home> 10: <remote>agency.Agency</remote> 11: <ejb-class>agency.AgencyBean</ejb-class> 12: <session-type>Stateless</session-type> 13: <transaction-type>Bean</transaction-type> 14: </session> 15: <session> 16: <display-name>AdvertiseBean</display-name> 17: <ejb-name>AdvertiseBean</ejb-name> 18: <home>agency.AdvertiseHome</home> 19: <remote>agency.Advertise</remote> 20: <ejb-class>agency.AdvertiseBean</ejb-class> 21: <session-type>Stateful</session-type> 22: <transaction-type>Bean</transaction-type> 23: </session> 24: </enterprise-beans> 25: </ejb-jar> Imagine that a different application (or a future version of J2EE) decided that stateless and stateful Session beans were sufficiently different to warrant using different elements. For example, <Stateless> <ejb-name>AgencyBean</ejb-name> … </Stateless> <Stateful> <ejb-name>AdvertiseBean</ejb-name> … </Stateful> To make this transformation, you need a rule that can generate an element whose name is derived from the original XML document. The XSL element that does this is called <xsl:element>, and the transformation shown previously is achieved by the following rule: <xsl:template match=”session”> <xsl:element name=”{./session-type}”> <xsl:apply-templates/> </xsl:element> 772 Day 17 21 0672323842 CH17 3/20/02 9:32 AM Page 772 Transforming XML Documents 773 17 </xsl:template> <xsl:template match=”session/session-type”/> The name attribute to the <xsl:element> is the name of the element to define. In this example, the name is the value of the session-type child element (remember that braces take the value of a node when defining attributes). The second rule in the previous example (<xsl:element name=”{./session-type}”>) ensures that the session-type child element is not included in the output document. Sadly, there is one major problem with the previous example. All other elements are out- put using their text values, the element start and end tags and attributes have been lost from the document. The problem can be overcome using the <xsl:copy> element. The <xsl:copy> element is used to copy elements from the XML source to the output document. The following rule is an identity transformation rule (the document is copied without any changes): <xsl:template match=”*|@*|comment()|processing-instruction()|text()”> <xsl:copy> <xsl:apply-templates ➥select=”*|@*|comment()|processing-instruction()|text()”/> </xsl:copy> </xsl:template> The template matches all elements and uses the <xsl:copy> element to copy the matched element. The body of the <xsl:copy> element must apply the template rules to the body of the matched XML node; otherwise, no output will occur. The full stylesheet for transforming the old style DD into the new style is shown in Listing 17.15. The output from applying this stylesheet is shown in Listing 17.16. LISTING 17.15 Full Text of session.xsl 1: <?xml version=”1.0”?> 2: <xsl:stylesheet version=”1.0” ➥xmlns:xsl=”http://www.w3.org/1999/XSL/Transform”> 3: <xsl:template match=”session”> 4: <xsl:element name=”{./session-type}”> 5: <xsl:apply-templates/> 6: </xsl:element> 7: </xsl:template> 8: <xsl:template match=”session/session-type”/> 9: <xsl:template match=”*|@*|comment()|processing-instruction()|text()”> 10: <xsl:copy> 11: <xsl:apply-templates ➥select=”*|@*|comment()|processing-instruction()|text()”/> 12: </xsl:copy> 13: </xsl:template> 14: </xsl:stylesheet> 21 0672323842 CH17 3/20/02 9:32 AM Page 773 LISTING 17.16 Applying session.xsl to dd.xml 1: >java org.apache.xalan.xslt.Process -in XML/dd.xml -xsl XSL/session.xsl 2: <?xml version=”1.0” encoding=”UTF-8”?> 3: <! DOCTYPE ejb-jar PUBLIC ➥’-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN’ ➥’http://java.sun.com/dtd/ejb-jar_2_0.dtd’ > 4: <ejb-jar> 5: <display-name>Agency</display-name> 6: <enterprise-beans> 7: <Stateless> 8: <display-name>AgencyBean</display-name> 9: <ejb-name>AgencyBean</ejb-name> 10: <home>agency.AgencyHome</home> 11: <remote>agency.Agency</remote> 12: <ejb-class>agency.AgencyBean</ejb-class> 13: 14: <transaction-type>Bean</transaction-type> 15: </Stateless> 16: <Stateful> 17: <display-name>AdvertiseBean</display-name> 18: <ejb-name>AdvertiseBean</ejb-name> 19: <home>agency.AdvertiseHome</home> 20: <remote>agency.Advertise</remote> 21: <ejb-class>agency.AdvertiseBean</ejb-class> 22: 23: <transaction-type>Bean</transaction-type> 24: </Stateful> 25: </enterprise-beans> 26: </ejb-jar> Attributes and Attribute Sets In the example jobSummary document in Listing 17.3 and the stylesheet table.xsl in Listing 17.10, you might like to be able to use a hyperlink to link the customer name to a URL of the form /agency/advertise?customer=<customer_name> Using the sample data from Listing 17.3, the output heading for a job for winston would look as follows: <H2>Job ref: <A HREF=”/agency/advertise?winston”>winston</A>/Cigar Trimmer</H2> Here, the value of the new attribute is derived from the XML source document. This can be achieved by using the <xsl:attribute> element, as shown in the following: <xsl:template match=”job”> <H2>Job ref: 774 Day 17 21 0672323842 CH17 3/20/02 9:32 AM Page 774 Transforming XML Documents 775 17 <A> <xsl:attribute name=”HREF”> /agency/advertise?<xsl:value-of select=”@customer”/> </xsl:attribute> <xsl:value-of select=”@customer”/> </A>/<xsl:value-of select=”@reference”/></H2> <TABLE border=”1”> <xsl:apply-templates/> </TABLE> </xsl:template> The <xsl:attribute> element defines an attribute for the enclosing element (in this case, <A>). More than one attribute can be defined, but all attributes must be defined before any other text or child nodes in the element. Sometimes, the same attributes must be defined for many different tags. This is a com- mon requirement when applying styles to HTML tables. Consider making every cell in the table contain text with a blue sans-serif font. You could define the style separately for every cell in the table, but this is hard to maintain should the style requirements change. Alternatively, you could use Cascading Style Sheets (CSS), but the most popular browsers do not support CSS in a consistent manner. An XSL solution is to use an attribute set. The <xsl:attribute-set> element defines the attributes you can apply to multiple ele- ments. An <xsl:attribute-set> defining a blue sans-serif font is as follows: <xsl:attribute-set name=”rowStyle”> <xsl:attribute name=”face”>Arial,sans-serif</xsl:attribute> <xsl:attribute name=”color”>blue</xsl:attribute> </xsl:attribute-set> An attribute set is applied by using the xsl:use-attribute-sets attribute with an ele- ment. For example <xsl:template match=”skill|location”> <TR><TD><FONT xsl:use-attribute-sets=”rowStyle”> <xsl:value-of select=”name()”/> </FONT></TD><TD><FONT xsl:use-attribute-sets=”rowStyle”> <xsl:value-of select=”.”/> </FONT></TD></TR> </xsl:template> The transformed table definition for the job skill and location elements is as follows: <TABLE border=”1”> <TR> <TD><FONT face=”Arial,sans-serif” color=”blue”>location</FONT></TD> <TD><FONT face=”Arial,sans-serif” color=”blue”>London</FONT></TD> </TR> 21 0672323842 CH17 3/20/02 9:32 AM Page 775 [...]... pattern providing a strategy using EJBs 22 067232 384 2 CH 18 3/20/02 9:26 AM Page 797 Patterns 797 Patterns Within J2EE As noted previously, certain patterns occur within the J2EE environment itself, including the following: • The Proxy pattern (GoF) is used widely in J2EE Examples include RMI stubs as client-side proxies and EJB objects as server-side proxies • An EJB home interface acts as a Singleton... web.OptionTagTEI 78: empty 79: 80 : selected 81 : false 82 : true 83 : java.util.String[] 84 : 85 : 86 : default 87 : false 88 : true 89 : java.util.String 90: 91: 92: 21 067232 384 2... advertiser’s details in a single method call You can apply the Value Object pattern to convert the repeated method calls into a single method call that returns a single JavaBean This single JavaBean would contain all of the required information To show this pattern-based refactoring in practice, consider two forms of the Advertise interface The original Advertise interface is shown in Listing 18. 1 and has one... property defined on the advertiser The interaction between the client and the Session EJB when loading the advertiser’s details is shown in Figure 18. 3 LISTING 18. 1 Original Advertise Interface 1: public interface Advertise extends EJBObject 2: { 3: void updateDetails (String name, String email, String[] Address) 4: throws RemoteException; 5: String getLogin() throws RemoteException; 6: String getName()... 17 21 067232 384 2 CH17 3/20/02 9:32 AM Page 786 786 Day 17 LISTING 17.20 Continued 31: 32: 33: 34: 35: 36: Finally, Figure 17.4 shows a screen snapshot of how your transformed HTML page should appear in a Web browser FIGURE 17.4 Applying 22 067232 384 2 CH 18 3/20/02 9:26 AM Page 787 WEEK 3 DAY 18 Patterns It has often been said that software engineering is... identifies a portable device independent grammar (XSL-FO) for defining formatting requirements and the document data XSL-FO is not being widely adopted by the industry at the present time You have now finished your excursion into XML Tomorrow, you will return to Java programming and the J2EE platform to study Java and J2EE design patterns 17 21 067232 384 2 CH17 3/20/02 9:32 AM Page 782 782 Day 17 Q&A Q What... document and perform the XML document transformation 21 067232 384 2 CH17 3/20/02 9:32 AM Page 781 Transforming XML Documents 781 An XSLT translet can be invoked from the command line or included in a developer’s application The XLST compiler technology is very new and still maturing (and changing) as this book is being written in late 2001 For more information and to download the xsltc technology, take... logic being undertaken • Performance In some ways, a Session Facade will reduce the level of performance because extra code and method calls are introduced However, designing the Session Facade interface to offer a coarse-grained, business-oriented interface in place of the underlying entity bean’s fine-grained, data-oriented interface can frequently offset any reduction in performance because it reduces... technology has matured, J2EE- specific patterns have been discovered that should make your life as a J2EE designer and developer easier Today, you will • Explore how the use of patterns can improve the design of systems • Examine some of the J2EE- specific patterns currently documented 22 067232 384 2 CH 18 3/20/02 9:26 AM Page 788 788 Day 18 • Discover some of the J2EE patterns that are applied in the case study... where the node occurs in the document tree structure The following example adds numbers to job definitions: Job ref: … Listing 17. 18 shows the final stylesheet for transforming the job.xml document using numbers to count jobs and skills within a job The resulting Web page is shown in Figure 17.3 LISTING 17. 18 Full Text of tableCount.xsl . given start point • Use letters or roman numerals instead of decimal integers or insert leading zeroes to make fixed-width numbers 7 78 Day 17 LISTING 17. 18 Continued 21 067232 384 2 CH17 3/20/02. XML. 7 68 Day 17 21 067232 384 2 CH17 3/20/02 9:32 AM Page 7 68 Transforming XML Documents 769 17 The following example shows one way of inserting a piece of JavaScript into your Web page (using comments,. document transformation. 780 Day 17 21 067232 384 2 CH17 3/20/02 9:32 AM Page 780 Transforming XML Documents 781 17 An XSLT translet can be invoked from the command line or included in a developer’s application. The