jsp标签
目录
一、标签语言的特点
二、自定义标签的使用步骤
三、JSP标签生命周期图
四、JSP标签实践
一、标签语言的特点
代码展示：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
Insert title here
true
false
运行结果：
二、自定义标签的使用步骤
通过点击c：if标签，可以链接跳到c.tld文件中、而.tld文件就是c标签库的定义配置文件
该配置文件源码：
JSTL 1.1 core library
JSTL core
1.1
c
http://java.sun.com/jsp/jstl/core
Provides core validation features for JSTL tags.
org.apache.taglibs.standard.tlv.JstlCoreTLV
Catches any Throwable that occurs in its body and optionally
exposes it.
catch
org.apache.taglibs.standard.tag.common.core.CatchTag
JSP
Name of the exported scoped variable for the
exception thrown from a nested action. The type of the
scoped variable is the type of the exception thrown.
var
false
false
Simple conditional tag that establishes a context for
mutually exclusive conditional operations, marked by
<when> and <otherwise>
choose
org.apache.taglibs.standard.tag.common.core.ChooseTag
JSP
Simple conditional tag, which evalutes its body if the
supplied condition is true and optionally exposes a Boolean
scripting variable representing the evaluation of this condition
if
org.apache.taglibs.standard.tag.rt.core.IfTag
JSP
The test condition that determines whether or
not the body content should be processed.
test
true
true
boolean
Name of the exported scoped variable for the
resulting value of the test condition. The type
of the scoped variable is Boolean.
var
false
false
Scope for var.
scope
false
false
Retrieves an absolute or relative URL and exposes its contents
to either the page, a String in 'var', or a Reader in 'varReader'.
import
org.apache.taglibs.standard.tag.rt.core.ImportTag
org.apache.taglibs.standard.tei.ImportTEI
JSP
The URL of the resource to import.
url
true
true
Name of the exported scoped variable for the
resource's content. The type of the scoped
variable is String.
var
false
false
Scope for var.
scope
false
false
Name of the exported scoped variable for the
resource's content. The type of the scoped
variable is Reader.
varReader
false
false
Name of the context when accessing a relative
URL resource that belongs to a foreign
context.
context
false
true
Character encoding of the content at the input
resource.
charEncoding
false
true
The basic iteration tag, accepting many different
collection types and supporting subsetting and other
functionality
forEach
org.apache.taglibs.standard.tag.rt.core.ForEachTag
org.apache.taglibs.standard.tei.ForEachTEI
JSP
Collection of items to iterate over.
items
false
true
java.lang.Object
If items specified:
Iteration begins at the item located at the
specified index. First item of the collection has
index 0.
If items not specified:
Iteration begins with index set at the value
specified.
begin
false
true
int
If items specified:
Iteration ends at the item located at the
specified index (inclusive).
If items not specified:
Iteration ends when index reaches the value
specified.
end
false
true
int
Iteration will only process every step items of
the collection, starting with the first one.
step
false
true
int
Name of the exported scoped variable for the
current item of the iteration. This scoped
variable has nested visibility. Its type depends
on the object of the underlying collection.
var
false
false
Name of the exported scoped variable for the
status of the iteration. Object exported is of type
javax.servlet.jsp.jstl.core.LoopTagStatus. This scoped variable has nested
visibility.
varStatus
false
false
Iterates over tokens, separated by the supplied delimeters
forTokens
org.apache.taglibs.standard.tag.rt.core.ForTokensTag
JSP
String of tokens to iterate over.
items
true
true
java.lang.String
The set of delimiters (the characters that
separate the tokens in the string).
delims
true
true
java.lang.String
Iteration begins at the token located at the
specified index. First token has index 0.
begin
false
true
int
Iteration ends at the token located at the
specified index (inclusive).
end
false
true
int
Iteration will only process every step tokens
of the string, starting with the first one.
step
false
true
int
Name of the exported scoped variable for the
current item of the iteration. This scoped
variable has nested visibility.
var
false
false
Name of the exported scoped variable for the
status of the iteration. Object exported is of
type
javax.servlet.jsp.jstl.core.LoopTag
Status. This scoped variable has nested
visibility.
varStatus
false
false
Like <%= ... >, but for expressions.
out
org.apache.taglibs.standard.tag.rt.core.OutTag
JSP
Expression to be evaluated.
value
true
true
Default value if the resulting value is null.
default
false
true
Determines whether characters <,>,&,'," in the
resulting string should be converted to their
corresponding character entity codes. Default value is
true.
escapeXml
false
true
Subtag of <choose> that follows <when> tags
and runs only if all of the prior conditions evaluated to
'false'
otherwise
org.apache.taglibs.standard.tag.common.core.OtherwiseTag
JSP
Adds a parameter to a containing 'import' tag's URL.
param
org.apache.taglibs.standard.tag.rt.core.ParamTag
JSP
Name of the query string parameter.
name
true
true
Value of the parameter.
value
false
true
Redirects to a new URL.
redirect
org.apache.taglibs.standard.tag.rt.core.RedirectTag
JSP
The URL of the resource to redirect to.
url
false
true
Name of the context when redirecting to a relative URL
resource that belongs to a foreign context.
context
false
true
Removes a scoped variable (from a particular scope, if specified).
remove
org.apache.taglibs.standard.tag.common.core.RemoveTag
empty
Name of the scoped variable to be removed.
var
true
false
Scope for var.
scope
false
false
Sets the result of an expression evaluation in a 'scope'
set
org.apache.taglibs.standard.tag.rt.core.SetTag
JSP
Name of the exported scoped variable to hold the value
specified in the action. The type of the scoped variable is
whatever type the value expression evaluates to.
var
false
false
Expression to be evaluated.
value
false
true
Target object whose property will be set. Must evaluate to
a JavaBeans object with setter property property, or to a
java.util.Map object.
target
false
true
Name of the property to be set in the target object.
property
false
true
Scope for var.
scope
false
false
Creates a URL with optional query parameters.
url
org.apache.taglibs.standard.tag.rt.core.UrlTag
JSP
Name of the exported scoped variable for the
processed url. The type of the scoped variable is
String.
var
false
false
Scope for var.
scope
false
false
URL to be processed.
value
false
true
Name of the context when specifying a relative URL
resource that belongs to a foreign context.
context
false
true
Subtag of <choose> that includes its body if its
condition evalutes to 'true'
when
org.apache.taglibs.standard.tag.rt.core.WhenTag
JSP
The test condition that determines whether or not the
body content should be processed.
test
true
true
boolean
自己创一个.tld文件
Ctrl+f -->搜索file 出现如图
将c:if中的配置文件的内容复制一份放进自己的配置文件中 改一下路径
JSTL 1.1 core library
JSTL core
1.1
z
http://jsp.veryedu.cn
Provides core validation features for JSTL tags.
org.apache.taglibs.standard.tlv.JstlCoreTLV
Catches any Throwable that occurs in its body and optionally
exposes it.
catch
org.apache.taglibs.standard.tag.common.core.CatchTag
JSP
Name of the exported scoped variable for the
exception thrown from a nested action. The type of the
scoped variable is the type of the exception thrown.
var
false
false
Simple conditional tag that establishes a context for
mutually exclusive conditional operations, marked by
<when> and <otherwise>
choose
org.apache.taglibs.standard.tag.common.core.ChooseTag
JSP
Simple conditional tag, which evalutes its body if the
supplied condition is true and optionally exposes a Boolean
scripting variable representing the evaluation of this condition
if
org.apache.taglibs.standard.tag.rt.core.IfTag
JSP
The test condition that determines whether or
not the body content should be processed.
test
true
true
boolean
Name of the exported scoped variable for the
resulting value of the test condition. The type
of the scoped variable is Boolean.
var
false
false
Scope for var.
scope
false
false
Retrieves an absolute or relative URL and exposes its contents
to either the page, a String in 'var', or a Reader in 'varReader'.
import
org.apache.taglibs.standard.tag.rt.core.ImportTag
org.apache.taglibs.standard.tei.ImportTEI
JSP
The URL of the resource to import.
url
true
true
Name of the exported scoped variable for the
resource's content. The type of the scoped
variable is String.
var
false
false
Scope for var.
scope
false
false
Name of the exported scoped variable for the
resource's content. The type of the scoped
variable is Reader.
varReader
false
false
Name of the context when accessing a relative
URL resource that belongs to a foreign
context.
context
false
true
Character encoding of the content at the input
resource.
charEncoding
false
true
The basic iteration tag, accepting many different
collection types and supporting subsetting and other
functionality
forEach
org.apache.taglibs.standard.tag.rt.core.ForEachTag
org.apache.taglibs.standard.tei.ForEachTEI
JSP
Collection of items to iterate over.
items
false
true
java.lang.Object
If items specified:
Iteration begins at the item located at the
specified index. First item of the collection has
index 0.
If items not specified:
Iteration begins with index set at the value
specified.
begin
false
true
int
If items specified:
Iteration ends at the item located at the
specified index (inclusive).
If items not specified:
Iteration ends when index reaches the value
specified.
end
false
true
int
Iteration will only process every step items of
the collection, starting with the first one.
step
false
true
int
Name of the exported scoped variable for the
current item of the iteration. This scoped
variable has nested visibility. Its type depends
on the object of the underlying collection.
var
false
false
Name of the exported scoped variable for the
status of the iteration. Object exported is of type
javax.servlet.jsp.jstl.core.LoopTagStatus. This scoped variable has nested
visibility.
varStatus
false
false
Iterates over tokens, separated by the supplied delimeters
forTokens
org.apache.taglibs.standard.tag.rt.core.ForTokensTag
JSP
String of tokens to iterate over.
items
true
true
java.lang.String
The set of delimiters (the characters that
separate the tokens in the string).
delims
true
true
java.lang.String
Iteration begins at the token located at the
specified index. First token has index 0.
begin
false
true
int
Iteration ends at the token located at the
specified index (inclusive).
end
false
true
int
Iteration will only process every step tokens
of the string, starting with the first one.
step
false
true
int
Name of the exported scoped variable for the
current item of the iteration. This scoped
variable has nested visibility.
var
false
false
Name of the exported scoped variable for the
status of the iteration. Object exported is of
type
javax.servlet.jsp.jstl.core.LoopTag
Status. This scoped variable has nested
visibility.
varStatus
false
false
Like <%= ... >, but for expressions.
out
org.apache.taglibs.standard.tag.rt.core.OutTag
JSP
Expression to be evaluated.
value
true
true
Default value if the resulting value is null.
default
false
true
Determines whether characters <,>,&,'," in the
resulting string should be converted to their
corresponding character entity codes. Default value is
true.
escapeXml
false
true
Subtag of <choose> that follows <when> tags
and runs only if all of the prior conditions evaluated to
'false'
otherwise
org.apache.taglibs.standard.tag.common.core.OtherwiseTag
JSP
Adds a parameter to a containing 'import' tag's URL.
param
org.apache.taglibs.standard.tag.rt.core.ParamTag
JSP
Name of the query string parameter.
name
true
true
Value of the parameter.
value
false
true
Redirects to a new URL.
redirect
org.apache.taglibs.standard.tag.rt.core.RedirectTag
JSP
The URL of the resource to redirect to.
url
false
true
Name of the context when redirecting to a relative URL
resource that belongs to a foreign context.
context
false
true
Removes a scoped variable (from a particular scope, if specified).
remove
org.apache.taglibs.standard.tag.common.core.RemoveTag
empty
Name of the scoped variable to be removed.
var
true
false
Scope for var.
scope
false
false
Sets the result of an expression evaluation in a 'scope'
set
org.apache.taglibs.standard.tag.rt.core.SetTag
JSP
Name of the exported scoped variable to hold the value
specified in the action. The type of the scoped variable is
whatever type the value expression evaluates to.
var
false
false
Expression to be evaluated.
value
false
true
Target object whose property will be set. Must evaluate to
a JavaBeans object with setter property property, or to a
java.util.Map object.
target
false
true
Name of the property to be set in the target object.
property
false
true
Scope for var.
scope
false
false
Creates a URL with optional query parameters.
url
org.apache.taglibs.standard.tag.rt.core.UrlTag
JSP
Name of the exported scoped variable for the
processed url. The type of the scoped variable is
String.
var
false
false
Scope for var.
scope
false
false
URL to be processed.
value
false
true
Name of the context when specifying a relative URL
resource that belongs to a foreign context.
context
false
true
Subtag of <choose> that includes its body if its
condition evalutes to 'true'
when
org.apache.taglibs.standard.tag.rt.core.WhenTag
JSP
The test condition that determines whether or not the
body content should be processed.
test
true
true
boolean
借用一下c标签的配置文件
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="http://jsp.veryedu.cn" prefix="z"%>
Insert title here
true
false
运行结果：
结论：
1、自定义标签是与tld文件相关的
2、标签库中的标签与tld中的tag元素有关，也就是跟tag元素对应的助手类有关
自己的配置文件
JSTL 1.1 core library
JSTL core
1.1
z
http://jsp.veryedu.cn
Provides core validation features for JSTL tags.
org.apache.taglibs.standard.tlv.JstlCoreTLV
demo1
com.cdl.tag.DemoTag1
JSP
测试代码：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="http://jsp.veryedu.cn" prefix="z"%>
Insert title here
xx
①当没标签体时的结果
②、有标签体时的结果
三、JSP标签生命周期图
结论：
1、有标签体的情况下 默认会调用助手类的doStartTag，doAfterBody，doEndTag方法
2、如果将doStartTag的返回值改为skip_body，那么doAfterBody就不会调用执行（路线1）
3、如果如果将doStartTag的返回值改为EVAL_BODY_INCLUDE，那么doAfterBody就不会调用执行 （路线2）
4、如果如果将doAfterBody的返回值改为EVAL_BODY_AGAIN，那么就会循环 （路线3）
四、JSP标签实践
写一个if标签
tld文件
JSTL 1.1 core library
JSTL core
1.1
z
http://jsp.veryedu.cn
Provides core validation features for JSTL tags.
org.apache.taglibs.standard.tlv.JstlCoreTLV
if
com.cdl.tag.IfTag
JSP
test
true
true
助手类：
package com.cdl.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
* if标签：
* 分析：
* 如果满足条件，就打印标签体-->dostarttag的返回值eval_body_include
* 如果不满足条件，就不输出标签体-->dostarttag的返回值skip_body
* 需要获取到是否满足条件的结果值，那么该标签就有一个属性，属性值是Boolean
*
* @author 陈冬丽
*
*/
public class IfTag extends BodyTagSupport {
private boolean test;
public boolean isTest() {
return test;
}
public void setTest(boolean test) {
this.test = test;
}
@Override
public int doStartTag() throws JspException {
return test ? EVAL_BODY_INCLUDE :SKIP_BODY;
}
}
运用：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="http://jsp.veryedu.cn" prefix="z"%>
Insert title here
<%-- xx --%>
true
false
结果图：
set和out标签
ltd的配置文件
JSTL 1.1 core library
JSTL core
1.1
z
http://jsp.veryedu.cn
Provides core validation features for JSTL tags.
org.apache.taglibs.standard.tlv.JstlCoreTLV
if
com.cdl.tag.IfTag
JSP
test
true
true
set
com.cdl.tag.SetTag
JSP
var
true
false
value
true
true
out
com.cdl.tag.OutTag
JSP
value
true
true
助手类：
settag:
package com.cdl.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
* 数据标签：存贮数据的
* 作用域：pagecontext，request，session，application（servletcontext）
*
* 要存贮数据：以键值对的方式进行存贮，分析得来该标签有两个属性
*
* @author 陈冬丽
*
*/
public class SetTag extends BodyTagSupport{
private String var;
private Object value;
public String getVar() {
return var;
}
public void setVar(String var) {
this.var = var;
}
public Object getValue() {
return value;
}
public void setValue(Object value) {
this.value = value;
}
@Override
public int doStartTag() throws JspException {
//要存贮数据：以键值对的方式进行存贮，分析得来该标签有两个属性
pageContext.setAttribute(var, value);
return super.doStartTag();
}
}
outtag:
package com.cdl.tag;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
* servlet中后台代码前台输出内容 out.print
* 将数据输出到前台 首先拿到输出流
* @author 陈冬丽
*
*/
public class OutTag extends BodyTagSupport{
private Object value;
public Object getValue() {
return value;
}
public void setValue(Object value) {
this.value = value;
}
@Override
public int doStartTag() throws JspException {
JspWriter out = pageContext.getOut();
try {
out.print(value);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return super.doStartTag();
}
}
测试代码：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="http://jsp.veryedu.cn" prefix="z"%>
Insert title here
<%-- xx --%>
true
false
运行结果：
