自定义JSP标签【上】

<!DOCTYPE taglib
  PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
   "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<!-- 标签库描述符 -->
<taglib xmlns="http://java.sun.com/JSP/TagLibraryDescriptor">
<tlib-version>1.0</tlib-version>
  <jsp-version>1.2</jsp-version>
  <short-name>Simple Tags</short-name>
  <uri>/ctb</uri>
  <tag>
    <name>out</name>
    <tag-class>com.ctb.tag.OutTag</tag-class>
    <body-content>empty</body-content>
    <attribute>
      <name>val</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <description>out标签val属性，用于输出val的值</description>
    </attribute>
    <attribute>
      <name>defaultVal</name>
      <required>false</required>
      <rtexprvalue>false</rtexprvalue>
      <description>定义默认值</description>
    </attribute>
  </tag>
  <tag>
    <name>if</name>
    <tag-class>com.ctb.tag.IfTag</tag-class>
    <body-content>jsp</body-content>
    <attribute>
      <name>test</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <description>if标签</description>
    </attribute>
  </tag>
   <tag>
    <name>foreach</name>
    <tag-class>com.ctb.tag.ForeachTag</tag-class>
    <body-content>jsp</body-content>
    <attribute>
      <name>items</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.Object</type>
    </attribute>
    <attribute>
      <name>var</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>
    </attribute>
  </tag>
</taglib>

package com.ctb.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
import com.mysql.jdbc.StringUtils;
/**
 * out助手类
 * @author biao
 *
 */
public class OutTag extends BodyTagSupport {
  private String val;
  private String defaultVal;
  public void setVal(String val) {
    this.val = val;
  }
  public void setDefaultVal(String defaultVal) {
    this.defaultVal = defaultVal;
  }
  @Override
  public int doStartTag() throws JspException {
    JspWriter out = this.pageContext.getOut();
    try {
      if(StringUtils.isNullOrEmpty(val)) {
        out.println(this.defaultVal);
      } else {
        out.println(this.val);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
    return SKIP_BODY;
  }
}

package com.ctb.tag;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * if助手类
 * @author biao
 *
 */
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() { 
    if(this.isTest()) {
      return EVAL_BODY_INCLUDE;
    } 
    return SKIP_BODY;
  }
}

package com.ctb.tag;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * foreach助手类
 * @author 86155
 *
 */
public class ForeachTag extends BodyTagSupport{
  //存放数据源
  private List<?> items;
  private String var;
  public List<?> getItems() {
    return items;
  }
  public void setItems(List<?> items) {
    this.items = items;
  }
  public String getVar() {
    return var;
  }
  public void setVar(String var) {
    this.var = var;
  }
  @Override
  public int doStartTag() {
    if(Objects.isNull(this.items) || this.items.size() == 0) {
      return SKIP_BODY;
    }
    Iterator<?> iterator = this.items.iterator();
    Object obj = iterator.next();
    this.pageContext.setAttribute(var, obj);
    this.pageContext.setAttribute("iterator", iterator);
    return EVAL_BODY_INCLUDE;
  }
  @Override
  public int doAfterBody() {
    Iterator<?> it = (Iterator<?>)this.pageContext.getAttribute("iterator");
    if(it.hasNext()) {
      this.pageContext.setAttribute(var, it.next());
      return EVAL_BODY_AGAIN;
    }
    return SKIP_BODY;
  }
}

<%@page import="com.ctb.tag.StudentAdd"%>
<%@page import="com.ctb.tag.Student"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@taglib prefix="c" uri="/ctb" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
  <%
    request.setAttribute("name", "");
  %>
  <!-- out 标签 -->
  <c:out val="${name}" defaultVal="--"/>
  <c:if test="${2 == 2}">
    测试if(2 == 2)
  </c:if>
  <c:if test="${1 != 12}">
    测试if(1 != 12)
  </c:if>
  <p>
<!--自定义foreach标签 -->
<%
//测试数据
List<Student> stu=StudentAdd.getStu();
//将数据保存在request对象中
request.setAttribute("stu", stu);
%>
<c:foreach items="${stu }" var="stu">
<c:out val="${stu.sid }"/>
<c:out val="${stu.sname }"/>
<c:out val="${stu.age }"/>
</c:foreach>
</body>
</html>