1、自定义标签语言特点
<开始标签 属性="属性值">标签体</结束标签>
空标签
<br/><hr/>
<开始标签></结束标签>
<开始标签/>
2. 自定义标签的开发及使用步骤
2.1 创建一个标签助手类(继承BodyTagSupport)
标签属性必须助手类的属性对应、且要提供对应get/set方法rtexprvalue
2.2 创建标签库描述文件(tld)，添加自定义标签的配置
注：tld文件必须保存到WEB-INF目录或其子目录
2.3 在JSP通过taglib指令导入标签库，并通过指定后缀
访问自定义标签
3、JSP自定义标签生命周期图：
SKIP_BODY：跳过主体
EVAL_BODY_INCLUDE：计算标签主体内容并[输出]
EVAL_BODY_BUFFERED：计算标签主体内容并[缓存]
EVAL_PAGE:计算页面的后续部分
SKIP_PAGE:跳过页面的后续部分
EVAL_BODY_AGAIN:再计算主体一次
4、自定义set跟out标签
分别创建一个set和out助手类
4、1：set助手类
package com.zl.jsp;
/*
* set助手类
*/
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
public class SetTag extends BodyTagSupport{
private static final long serialVersionUID = 1L;
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);//将值存入pageContext
return SKIP_BODY;
}
}
4、2：out助手类
package com.zl.jsp;
/*
* out助手类
*/
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 {
public Object getValue() {
return value;
}
public void setValue(Object value) {
this.value = value;
}
private Object value;
@Override
public int doStartTag() throws JspException {
JspWriter out=pageContext.getOut();
try {
out.write(value.toString());
} catch (IOException e) {
// TODO Auto-generated catch block
throw new RuntimeException(e);
}
return SKIP_BODY;
}
}
4、3：set跟out的tld文件
<!-- OUT标签 -->
<tag>
<name>out</name>
<tag-class>com.zl.jsp.OutTag</tag-class>
<body-content>empty</body-content>
<attribute>
<name>value</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<!-- SET标签 -->
<tag>
<name>set</name>
<tag-class>com.zl.jsp.SetTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>var</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>value</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
4、4：jsp页面演示set与out标签
<!-- set标签 -->
<!-- OUT标签 -->
<c:set var="name" value="hello" ></c:set>
<c:out value="${name }"/>
5、自定义if标签
5、1：if助手类
package com.zl.jsp;
/*
* if助手类
*/
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 {
if(!test) {
return SKIP_BODY;//不显示标签中间的内容
}
return EVAL_BODY_INCLUDE;//显示标签中间的内容
}
}
5.2：if标签的tld文件
<!-- if标签 -->
<tag>
<name>if</name>
<tag-class>com.zl.jsp.IfTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>test</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
5、3：jsp页面演示if标签
<!-- if标签 --> <c:if test="true" >zs</c:if> <c:if test="false">ls</c:if>
6、自定义Foreach标签
6、1：Foreach助手类
package com.zl.jsp;
/*
* Foreach助手类
*/
import java.util.Iterator;
import java.util.List;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
import javax.swing.text.html.HTML.Tag;
public class ForEachTag extends BodyTagSupport{
//集合
private List<Object> items;
//变量的名称
private String var;
public List<Object> getItems() {
return items;
}
public void setItems(List<Object> items) {
this.items = items;
}
public String getVar() {
return var;
}
public void setVar(String var) {
this.var = var;
}
@Override
public int doStartTag() throws JspException {
// TODO Auto-generated method stub
if(items==null||items.size()==0) {
return SKIP_BODY;
}
else {
Iterator<Object> i=items.iterator();
pageContext.setAttribute("s", i);
//第一次给变量进行赋值
pageContext.setAttribute(var, i.next());
return EVAL_BODY_INCLUDE;
}
}
@Override
public int doAfterBody() throws JspException {
Iterator<Object> it=(Iterator<Object>)pageContext.getAttribute("s");
while(it.hasNext()) {
//如何将循环读取出来的数据，显示在页面上
pageContext.setAttribute(var, it.next());
return EVAL_BODY_AGAIN;
}
return SKIP_BODY;
}
}
6、2：Foreach标签的tld文件
<!--foreach标签 --> <tag> <name>foreach</name> <tag-class>com.zl.jsp.ForEachTag</tag-class> <body-content>JSP</body-content> <attribute> <name>items</name> <required>true</required> <rtexprvalue>false</rtexprvalue> </attribute> <attribute> <name>var</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag>
6、3：jsp页面演示Foreach标签
<%
List list=new ArrayList();
list.add(new Student("sb1","zs"));
list.add(new Student("sb2","ls"));
list.add(new Student("sb3","ws"));
request.setAttribute("stus",list);
%>
<p:foreach items="${stus }" var="stu">
${stu.sid },${stu.sname }<br>
</p:foreach>
7、自定义select标签
7、1：select标签助手类
private static final long serialVersionUID = 1L;
private String id;
private String name;
private List<Object> items = new ArrayList<Object>();
private String textKey;
private String textval;
private String headTextKey;
private String headTextVal;
private String selectedval;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Object> getItems() {
return items;
}
public void setItems(List<Object> items) {
this.items = items;
}
public String getTextKey() {
return textKey;
}
public void setTextKey(String textKey) {
this.textKey = textKey;
}
public String getTextval() {
return textval;
}
public void setTextval(String textval) {
this.textval = textval;
}
public String getHeadTextKey() {
return headTextKey;
}
public void setHeadTextKey(String headTextKey) {
this.headTextKey = headTextKey;
}
public String getHeadTextVal() {
return headTextVal;
}
public void setHeadTextVal(String headTextVal) {
this.headTextVal = headTextVal;
}
public String getSelectedval() {
return selectedval;
}
public void setSelectedval(String selectedval) {
this.selectedval = selectedval;
}
@Override
public int doStartTag() throws JspException {
JspWriter out = pageContext.getOut();
try {
out.write(toHTML());
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return super.doStartTag();
}
/**
* 拼接出下拉列表所对应的select的html代码
* <select id='' name=''>
* <option value='-1'selected>=======请选择======</option>
* </select>
*/
private String toHTML() throws Exception {
StringBuilder sb = new StringBuilder();
sb.append("<select id='" + id + "' name='" + name + "'>");
if (headTextKey == null || "".equals(headTextKey) || headTextVal == null || "".equals(headTextVal)) {
sb.append("<option value='" + headTextKey + "' selected>" + headTextVal + "</option>");
}
String val;
String html;
for (Object obj : items) {
// 要让学生的id存入数据库，让学生的名字展示在jsp页面
// <option value='s001'>ls</option>
// obj sid sname
Field textKeyField = obj.getClass().getDeclaredField(textKey);
textKeyField.setAccessible(true);
val = (String) textKeyField.get(obj);
html = BeanUtils.getProperty(obj, textval);
if(val.equals(selectedval)) {
sb.append(" <option value='"+val+"'selected>"+html+"</option>");
}else {
sb.append("<option value='"+val+"'>"+html+"</option>");
}
}
sb.append("</select>");
return sb.toString();
}
7、2：select的tld文件
<!--select标签 -->
<tag> <name>select</name> <tag-class>com.jsp.ServletTag</tag-class> <body-content>JSP</body-content> <attribute> <name>id</name> <required>false</required> <rtexprvalue>flase</rtexprvalue> </attribute> <attribute> <name>name</name> <required>flase</required> <rtexprvalue>flase</rtexprvalue> </attribute> <attribute> <name>items</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> <attribute> <name>textKey</name> <required>true</required> <rtexprvalue>false</rtexprvalue> </attribute> <attribute> <name>textval</name> <required>true</required> <rtexprvalue>flase</rtexprvalue> </attribute> <attribute> <name>headTextKey</name> <required>false</required> <rtexprvalue>false</rtexprvalue> </attribute> <attribute> <name>headTextVal</name> <required>false</required> <rtexprvalue>flase</rtexprvalue> </attribute> <attribute> <name>selectedval</name> <required>false</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag>
7、3：jsp页面演示select标签
<p:select items="${stus }" textval="sname" textKey="sid"></p:select>
<p:select headTextKey="-1" headTextVal="===请选择学生===" items="${stus }" textval="sname" textKey="sid"></p:select>