Case Study of JSP Custom Tag
- 2021-10-13 08:18:12
- OfStack
This article introduces the case of JSP custom label for your reference, the specific contents are as follows
Case 1: Implement a basic anti-theft chain label
1. Label Handling Class
public class MyReferer extends BodyTagSupport {
private String site;
private String back;
public String getSite() {
return site;
}
public void setSite(String site) {
this.site = site;
}
public String getBack() {
return back;
}
public void setBack(String back) {
this.back = back;
}
public int doEndTag() throws JspException {
// Get JSP Context environment object
PageContext pageContext = this.pageContext;
// Get to request Object
HttpServletRequest request = (HttpServletRequest)pageContext.getRequest();
// Judge
String header = request.getHeader("referer");
if(header != null && header.startsWith(getSite())){
// Execute subsequent pages
return Tag.EVAL_PAGE;
}else{
// Redirection of pages
HttpServletResponse response = (HttpServletResponse)pageContext.getResponse();
try {
response.sendRedirect(getBack());
} catch (IOException e) {
e.printStackTrace();
}
// Do not execute
return Tag.SKIP_PAGE;
}
}
}
2. Describe the file
<?xml version="1.0" encoding="UTF-8"?>
<taglib
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
version="2.1">
<!-- 2. Writing Tag Library Description Files -->
<tlib-version>1.0</tlib-version>
<short-name>jnb</short-name>
<tag>
<name>referer</name>
<tag-class>cn.itcast.custom.MyReferer</tag-class>
<body-content>empty</body-content>
<attribute>
<name>site</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>back</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
</taglib>
3. Introduction and use
<%@taglib uri="/WEB-INF/referer.tld" prefix="my"%>
<my:referer site=http://localhost:8080/day11/list.jsp
back="/day11/list.jsp"/>
JSP 2.0 Custom Label
--SimpleTag interface
Defines the lifecycle method of the label handling class. doTag ()
--SimpleTagSupport category
All the methods of the SimpleTag interface are implemented, so we just need to inherit and override the class later.
Case 2: Implement your own if …. else tag
Objectives:
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<c:choose>
<c:when test="<%= 12>1 %>">
Greater than
</c:when>
<c:otherwise>
Less than
</c:otherwise>
</c:choose>
Analysis:
1. ChooseTag. java, 1 tag field attribute must be defined
public class ChooseTag extends SimpleTagSupport {
private boolean tag = true;
public boolean isTag() {
return tag;
}
public void setTag(boolean tag) {
this.tag = tag;
}
// Automatically execute when encountering labels
public void doTag() throws JspException, IOException {
// Get the tag body object
JspFragment body = this.getJspBody();
// Execute tag body
body.invoke(null);
super.doTag();
}
}
2. WhenTag.java
public class WhenTag extends SimpleTagSupport {
private boolean test;
public boolean isTest() {
return test;
}
public void setTest(boolean test) {
this.test = test;
}
// Automatically execute when encountering labels
public void doTag() throws JspException, IOException {
// Get the parent element
ChooseTag choose = (ChooseTag)this.getParent();
// Gets the tag variable value of the parent element
boolean parent = choose.isTag();
// Judge
if( parent && this.isTest() ){
// Execute tag body
JspFragment body = this.getJspBody();
body.invoke(null);
}
super.doTag();
}
}
3. Otherwise.java
public class OtherwiseTag extends SimpleTagSupport {
// Automatically execute when encountering labels
public void doTag() throws JspException, IOException {
// Get the parent element
ChooseTag choose = (ChooseTag)this.getParent();
// Gets the tag variable value of the parent element
boolean parent = choose.isTag();
// Judge
if(parent){
// Execute tag body
JspFragment body = this.getJspBody();
body.invoke(null);
}
super.doTag();
}
}
4. Describe the file
<?xml version="1.0" encoding="UTF-8"?>
<taglib
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
version="2.1">
<!-- 2. Writing Tag Library Description Files -->
<tlib-version>1.0</tlib-version>
<short-name>jnb</short-name>
<tag>
<name>choose</name>
<tag-class>cn.itcast.tags.ChooseTag</tag-class>
<body-content>scriptless</body-content> JSP2.0 Mode
</tag>
<tag>
<name>when</name>
<tag-class>cn.itcast.tags.WhenTag</tag-class>
<body-content>scriptless</body-content>
<attribute>
<name>test</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<tag>
<name>otherwise</name>
<tag-class>cn.itcast.tags.OtherwiseTag</tag-class>
<body-content>scriptless</body-content>
</tag>
</taglib>
5. Introduction and use
<%@taglib uri="/WEB-INF/ifelse.tld" prefix="jnb"%>
<jnb:choose>
<jnb:when test="<%= 1>2 %>">
Less than
</jnb:when>
<jnb:otherwise>
Greater than
</jnb:otherwise>
</jnb:choose>
Packaging Custom Tag Library
1. Create an taglibs folder
2. Copy all the class files corresponding to the tag handling classes together with the package to the directory in 1
3. Create an META-INF folder in the folder in 1
4. Copy the tld file to the META-INF directory
5. Edit the tld file to introduce the uri element: < uri > http://www.jnb.com < /uri > Provide the incoming url path
6. Packaging with the jar command: D:\ mytaglibs > jar cvf jnb.jar *
Summarize
Master how to use JSP 2.0 custom label development and packaging.
1. Create an taglibs folder
2. Copy all the class files corresponding to the tag-handling classes together with the package to the directory in 1
3. Create an META-INF folder in the folder in 1
4. Copy the tld file to the META-INF directory
5. Edit the tld file to introduce the uri element: < uri > http://www.jnb.com < /uri > Provide the incoming url path
6. Packaging with the jar command: D:\ mytaglibs > jar cvf jnb.jar *
Summarize
Master how to use JSP 2.0 custom label development and packaging.