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Developing JSP Custom Tag Libraries

Developing JSP Custom Tag Libraries. O'Reilly Conference on Enterprise Java, March 2001. Who I Am. Hans Bergsten hans@gefionsoftware.com President of Gefion software Member of the JSP working group (JCP) Author of JavaServer Pages (O’Reilly). Overview. The JSP promise

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Developing JSP Custom Tag Libraries

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  1. Developing JSP Custom Tag Libraries O'Reilly Conference on Enterprise Java, March 2001 Enterprise Java: Developing JSP Custom Tag Libraries

  2. Who I Am • Hans Bergsten • hans@gefionsoftware.com • President of Gefion software • Member of the JSP working group (JCP) • Author of JavaServer Pages (O’Reilly) Enterprise Java: Developing JSP Custom Tag Libraries

  3. Overview • The JSP promise • Custom Action Main Components • Implementation Examples • New in JSP 1.2 • Not a JSP introduction! Plenty of Code! Enterprise Java: Developing JSP Custom Tag Libraries

  4. Before JSP public void doGet(…) { ResultSet rs = getCustomers(“VIP”); out.println(“<ul>”); while (rs.next()) { out.println(“<li>” + rs.getString(“Name”); } Enterprise Java: Developing JSP Custom Tag Libraries

  5. With JSP 1.0 <jsp:useBean id=“cdb” class=“CustDB” /> <% ResultSet rs = cdb.getCustomers(“VIP”); %> <ul> <% while (rs.next()) { %> <li><%= rs.getString(“Name”) %> <% } %> Enterprise Java: Developing JSP Custom Tag Libraries

  6. With JSP 1.1 Custom Actions <foo:getVIPCust id=“vips” /> <ul> <foo:loop name=“vips” loopId=“cust” > <li><jsp:getProperty name=“cust” property=“name” /> </foo:loop> Enterprise Java: Developing JSP Custom Tag Libraries

  7. Types of Custom Actions • JSP for all MVC roles • Database access • EJB access • Input Validation • JSP just as View • Presentation • Conditional processing Enterprise Java: Developing JSP Custom Tag Libraries

  8. <foo:loop name=“vips” loopId=“cust”> <li> … </foo:loop> or <foo:getVIPCust id=“vips” /> XML element Opening tag Body Closing tag Shorthand notation for element without a body Custom Action Representation Enterprise Java: Developing JSP Custom Tag Libraries

  9. Custom Action Components • Tag handler class • Tag Library Descriptor (TLD) • TagExtraInfo subclass Enterprise Java: Developing JSP Custom Tag Libraries

  10. XXX implements Tag { setPageContext(…) setParam(...) setValue(…) doStartTag() doEndTag() <foo:ifEq param=“sale” value=“true”> <b>On Sale!</b> </foo:ifEq> Basic Tag Handler Enterprise Java: Developing JSP Custom Tag Libraries

  11. Implementing the IfEqTag public class IfEqTag extends TagSupport { … public int doStartTag() { ServletRequest req = pageContext.getRequest(); String paramValue = req.getParameter(param); if (value.equals(paramValue)) { return EVAL_BODY_INCLUDE; else { return SKIP_BODY; }} Enterprise Java: Developing JSP Custom Tag Libraries

  12. Tag Library Descriptor (TLD) <taglib> … <tag> <name>ifEq</name> <tagclass>com.foo.IfEqTag</tagclass> <bodycontent>JSP</bodycontent> Enterprise Java: Developing JSP Custom Tag Libraries

  13. Tag Library Descriptor (TLD), Cont’d <attribute> <name>param</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag> </taglib> Enterprise Java: Developing JSP Custom Tag Libraries

  14. JSP taglib Directive <%@ taglib uri=“/foolib” prefix=“foo” %> <foo:ifEq param=“sale” value=“true”> <b>On Sale!</b> </foo:ifEq> Enterprise Java: Developing JSP Custom Tag Libraries

  15. <%@ taglib prefix=“foo” uri=“/foolib” %> <foo:ifEq param=“sale”value=“true” ><b>On Sale!</b> </foo:ifEq> TLD<tag> <name>ifEq</name> <tagclass>XXX</tagclass> How It All Fits Together Tag handler Enterprise Java: Developing JSP Custom Tag Libraries

  16. Basic Tag Handler Examples • Conditional processing: • doStartTag() -> EVAL_BODY_INCLUDE, SKIP_BODY • doEndTag() -> EVAL_PAGE, SKIP_PAGE • Presentation: i18n, complex tables, etc. • Data access: database, EJB, etc. Enterprise Java: Developing JSP Custom Tag Libraries

  17. <foo:mail to=“...”> Dear <jsp:getProperty ...> ... </foo:mail> XXX impl. BodyTag { setPageContext(…) setTo(...) doStartTag() setBodyContent(...) doInitBody() doAfterBody() doEndTag() Processing the Element Body Enterprise Java: Developing JSP Custom Tag Libraries

  18. Buffering Hierarchy JspWriter <%@ taglib … %><html> Some text <jsp:getProperty .../> <foo:mail …>Dear <jsp:getProperty /> </foo:mail></html> BodyContent Enterprise Java: Developing JSP Custom Tag Libraries

  19. BodyContent class • JspWriter subclass, buffers the element body evaluation result for BodyTags • getReader() • getString() • writeOut(java.io.Writer out) • getEnclosingWriter() Enterprise Java: Developing JSP Custom Tag Libraries

  20. Implementing the MailTag public class MailTag extends BodyTagSupport { … public int doAfterBody() { mailBean.setTo(to); mailBean.setMsg(getBodyContent().getString()); mailBean.deliver(); return SKIP_BODY; }} Enterprise Java: Developing JSP Custom Tag Libraries

  21. BodyTag Handler Examples • Iterations • doAfterBody() -> EVAL_BODY_TAG, SKIP_BODY • Dynamic input, using other JSP elements to create it • Static input spanning multiple lines, e.g. SQL, XML, other non-JSP syntax. Enterprise Java: Developing JSP Custom Tag Libraries

  22. Validating Element Syntax • Two mechanisms: • Container validation using the TLD:<attribute> <name>param</name> <required>true</required> </attribute> • Use a TagExtraInfo class with isValid() • Can be combined Enterprise Java: Developing JSP Custom Tag Libraries

  23. Validation with TagExtraInfo public class MailTEI extends TagExtraInfo { public boolean isValid(TagData data) { if (data.getAttribute(“to”) != null && data.getAttribute(“toList”) != null) { return false; // Mutually exclusive optional } if (data.getAttribute(“name”) != null && data.getAttribute(“property”) == null) { return false; // Dependent optional } return true; Enterprise Java: Developing JSP Custom Tag Libraries

  24. Letting Actions Cooperate • Through objects in a JSP scope:<foo:getVIPCust id=“vips” /><foo:loop name=“vips” loopId=“cust” > • Through direct method calls on the parent tag handler:<foo:redirect page=“some.jsp”> <foo:param name=“a” value=“b” /></foo:redirect> Enterprise Java: Developing JSP Custom Tag Libraries

  25. Coop Through Objects • Save the object in one tag handler:public int doXXX() { ... pageContext.setAttribute(id, value, scope);} • Get the object in another tag handler:public int doXXX() { … Object o = pageContext.findAttribute(name);} Enterprise Java: Developing JSP Custom Tag Libraries

  26. Scripting Variable Assignment public class GetVIPCustTEI extends TagExtraInfo { public VariableInfo[] getVariableInfo(TagData data) { VariableInfo vi = new VariableInfo[1]; vi[0] = new VariableInfo( data.getAttributeString(“id”), // Variable name “com.mycomp.CustBean”, // Variable type true, // Declare variable? VariableInfo.AT_END); // Assignment scope return vi; }} Enterprise Java: Developing JSP Custom Tag Libraries

  27. Coop Through Method Calls public class ParamTag extends TagSupport { public int doEndTag() { RedirectTag parent = (RedirectTag) findAncestorWithClass(this, RedirectTag.class); if (parent != null) { parent.setParam(name, URLEncoder.encode(value); } return EVAL_PAGE; }} Enterprise Java: Developing JSP Custom Tag Libraries

  28. JSP 1.2 Tag Library News • New Interfaces • IteratorTag, TryCatchFinally • Validation Enhancements • TagLibraryValidator class, TEI isValid() • Application & session event listeners • TLD can describe tag handler variables Enterprise Java: Developing JSP Custom Tag Libraries

  29. More Info • JSP Specificationhttp://java.sun.com/products/jsp/ • JavaServer Pages bookhttp://TheJSPBook.com/ • Jakarta Taglibs & Strutshttp://jakarta.apache.org/ • InstantOnline Basichttp://www.gefionsoftware.com/InstantOnline/ Enterprise Java: Developing JSP Custom Tag Libraries

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