哈喽啊铁子们今天分享的是jsp标签
老规矩 先看思维导图
目录
一,标签语言特点
二，自定义标签的开发及使用步骤
编辑
三、标签生命周期
四，c:if标签 c:set与c:out标签
一,标签语言特点
1.标签形式
对
true 标签体
2.标签分类：
标签分类：控制标签：例如if foreach 数据标签:out UI标签:input table 空标签：例如br,hr
没有标签体也能在网页中输出内容 称为UI标签
代码案例：
<%@ 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
下面是运行效果
二，自定义标签的开发及使用步骤
自定义标签的开发分为：
助手类(继承BodyTagSupport)
标签库描述文件（.tld）(按住Ctrl键点击c:if即可进入，.tld文件必须放在WEB_INF目录下或者其子目录下)
JSP页面通过taglib指令导入标签库
实例：z:if
助手类：继承BodyTagSupport 实现三个开发场景
jsp页面
运行结果
三、标签生命周期
① 返回值
SKIP_BODY 跳过主体
EVAL_BODY_INCLUDE 计算标签主体内容并输出
EVAL_BODY_AGAIN 再计算主体一次
SKIP_PAGE 跳过页面的后续
② 标签开发场景
package com.tsq.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
public class Demotag1 extends BodyTagSupport {
@Override
public int doStartTag() throws JspException {
System.out.println("=========== doStartTag==========");
// TODO Auto-generated method stub
return SKIP_BODY;
}
public class doAfterBody extends BodyTagSupport {
@Override
public int doStartTag() throws JspException {
System.out.println("=========== doAfterBody==========");
// TODO Auto-generated method stub
// int i=1;
// return EVAL_BODY_AGAIN;
return SKIP_PAGE;
}
}
@Override
public int doEndTag() throws JspException {
System.out.println("=========doEndTag===========");
return super.doEndTag();
}
}
四，c:if标签 c:set与c:out标签
了解了那么多理论知识，大多都是试验测试，不怎么好看运行结果，
而接下来我们就来利用我们了解的理论知识来实践一下：
4.1自定义几个属于自己的标签吧~
4.2 if标签的的定义
我们需要先建一个if标签类，继承助手类：定义一个if属性test：boolean类型
package com.tsq.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
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 {
// * 如果满足条件 就打印标签签体——dosarttag的返回值eval_boby_include
// * 如果不满足条件 就不输出标签体
return test ? EVAL_BODY_INCLUDE: SKIP_BODY;
}
}
我们写好这个标签类后就要去文件里写好相关的配置，我们把其他的配置全部删除，
留下一个范本：
JSTL 1.1 core library JSTL core 1.1 z http://jsp.tsq1.cn Provides core validation features for JSTL tags. org.apache.taglibs.standard.tlv.JstlCoreTLV demo1 com.tsq.tag.Demotag1 JSP var false false if com.tsq.tag.iftag JSP test false true set com.tsq.tag.settag JSP var true false out com.tsq.tag.outtag JSP value true true value com.tsq.tag.outtag JSP test false true 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
我们发现没有问题！
接着我们继续来试一下Set以及Out标签的定义：
Set标签类：这个我们就是拿到一个存储数据的地方：pageContext
package com.tsq.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.BodyTagSupport;
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 {
// PageContext.setAttribute(var,value);
return super.doStartTag();
}
}
我们继续定义标签类：
Out标签类：这个我们主要就是拿到一个输出流：pageContext.getOut();
package com.tsq.tag;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
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();
}
}
写好标签类后我们就统一tld文件配置一下：
demo1 com.tsq.tag.Demotag1 JSP var false false if com.tsq.tag.iftag JSP test false true set com.tsq.tag.settag JSP var true false out com.tsq.tag.outtag JSP value true true value com.tsq.tag.outtag JSP test false true
好了本次分享到此结束了我们下次见
