The Jstl of JSP

JSTL Overview:
Apache thing that relies on el;
Use Jstl to import Jstl1.2.jar
Four libraries:
Core: Kernel Library
FMT: formatting dates, numbers
SQL: Obsolete
XML: Obsolete
2. Import Tag Library
* Jar Package
* In the JSP page, <% @taglib prefix= "prefix" uri= "path"%>
======================================================
Core Tag Library Common tags (c tag)
1, out and set
<c:out value= "AAA"/>
<c:out value= "${aaa}"/>
<c:out value= "${aaa}" default= "BBB"/>
<c:out value= "${aaa}" default= "BBB" escapexml= "true"/> The default value is true to indicate escape;
<c:set var= "name" value= "value" scope= "Request"/>
var: variable Name value: Variable value scope: Set domain page/request/session/application If you do not declare default to page
2. Remove
<c:remove var= "a"/>
Scope: If you do not write the default delete all domain variable named a value, if specified only delete the specified;
3. URL
Value: Specify a path! He will automatically add the project name in front of the path.
<c:url value= "/index.jsp" > it will output/day13_1/index.jsp
The child label:<c:param> is used to add parameters to the URL, for example:
<c:url value= "/index.jsp" >
<c:param name= "username" value= "Zhangsan"/>
</c:url>
The result is:/day13_1/index.jsp?username=%ed%2c%d3%2d%4f URL encoding

var: Once this attribute is added, the URL is not exported to the page but added to the domain for saving;
Scope: Used with VAR to hold the specified domain of the URL
4. If
<c:if test= "Boolean value" > when the test value is true, execute the following statement
<c:set var= "A" value= "Hello"/>
<c:if test= "${not Empty A}" >
<c:if>
5, choose
<c:choose>
<c:when tedt= "" >...</c:when>
<c:when tedt= "" >...</c:when>
<c:when tedt= "" >...</c:when>
<c:otherwise>.....</c:otherwise>
</c:choose>
6. ForEach
It is used to iterate through arrays and collections, and it can also be counted in the form of loops!
Counting method:
<c:foreach var= "I" begin= "1" end= "step=" 2 "> equivalent to i>=1 i<=10 step=" Step "
${i}<br/>
</c:forEach>
var = loop variable
begin= Setting the loop variable from several beginnings
end= set the loop variable to a few ends
step= Set Step step defaults to 1
To iterate over arrays and collections:
1. Creating an array
<%
string[] str = {"Name", "value"}
Request.setattribute ("arr", str);
%>
2. Iterating through an array
<c:foreach items= "${str}" var= "S" >
${s}<br/>
</c:forEach>
Items: Arrays or collections to traverse
var: define each member to traverse
foreach Loop state:
You can use Varstatus to create loop state variables!
Count: Number of elements currently traversed
Last: Whether the current loop is the final lap
First: The first element, one lap
Index: Current element subscript
Current: Object
<%
arraylist<string>list= new arraylist<string> ();
List.add ("one");
List.add ("both");
List.add ("three");
Pagecontext.setattribute ("list", list);
%>
<c:foreach items= "${list}" var= "Ele" varstatus= "vs" >
${vs.index}${vs.count}${vs.first}${vs.last}${vs.current}
</c:forEach>
FMT Library:
Format Library
Import the/JSP/JSTL/FMT tag library first
1. Formatted date
<%
Date date = new Date ();
Request.setattribute ("date", date);
%>
<fmt:formatdate value= "${requestscope.date}" pattern= "Yyyy-mm-dd HH:MM:SS"/>
Value is a date class variable
pattern is the date format of the output
2. Format numbers
<%
Request.setattribute ("Num1", 3.1415926);
%>
<fmt:number value= "${requestscope.num1}" pattern= "0.00"/>
Pattern default number of decimal places, and default rounding, vacancy will be 0 to fill the position
<fmt:number value= "${requestscope.num1}" pattern= "#.##"/>
The difference is not to fill the position, are rounded;
Custom Tags:
1, Label processing class (the label is also an object, then you need to have a class first)
2. tld file, he is an XML
3, the page import TLD file location <%@ taglib prefix= "" uri= "TLD True Path"%>
* Label Processing class
Early Java EE provides interface Tag, later with a lot of implementation class, in order to operate convenient sun company provided interface Simpletag;
Jsptag is the father of tag and Simpletag.
We're using Simpletag, and here's how.
void Dotag (): This method is called every time the label is executed;
Jsptag getParent (): Returns the parent tag
void Setjspbody (Jspfragment jspbody): Set label body
void Setjspcontext (Jspcontext pc): Set Label Context Object PageContext is Jspcontext's son.
void SetParent (): Set parent tag
These methods are called by Tomcat itself, and the GetParent () method is called by ourselves, but is not used at all;
All setxxxxx methods are called before the Dotag method, so you can use the object that tomcat passed over in Dotag!
* Configure TLD Files:
TLD files are generally placed under Web-inf to ensure security
* Templates can be used in the TLD file of the core tag to borrow
<tag>
<name>mytag1</name>//Specify the name of the label
<tag-class>cn.itcast.tag.MyTag1</tag-class>//Specify Label class location
<body-content>empty</body-content>//Specify label body type, we use empty label here! For example:<br/> himself began to end himself
</tag>
To make it easier for us to use the implementation class Simpletagsupport, this class has automatically saved the stuff that Tomcat passed and provided a Get method

The Jstl of JSP