JSTL_自定义标签

来源：互联网发布：心电图工作站软件下载编辑：程序博客网时间：2024/06/09 22:49

1.自定义标签步骤

jsp引入tld文件及标签
tld文件描述页面标签
后端class标签类（TagClass）的关系

2.jsp页面标签——设计（创造）

标签结构：<前缀：标签名属性=”属性值”>标签体

3.extends TagSupport实现自定义标签

1.<%@ taglib prefix="mytag" uri="http://www.lps.com/mytag" %>

<mytag:nowTime format="yyyy-MM-dd HH:mm:ss" var="time" outEl="true">当前时间:${time}</mytag:nowTime>

<?xml version="1.0" encoding="UTF-8" ?>http://java.sun.com/xml/ns/javaee"    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"    version="2.1">  <description>web 1 tag</description>  <display-name>mytag</display-name>  <tlib-version>1.0</tlib-version>  <!-- 版本 -->  <short-name>mytag</short-name> <!-- 前缀 -->  http://www.lps.com/mytag>   <tag>    <name>nowTime</name> <!-- 标签名 -->    <tag-class>com.lps.tag.NowTimeTag</tag-class> <!-- 对应类 -->    <body-content>JSP</body-content> <!-- 标签体内容格式 -->    <attribute>  <!-- 属性 -->        <name>format</name> <!-- 属性名 -->        <required>false</required> <!-- 属性是不是必须添加 -->        <rtexprvalue>true</rtexprvalue> <!-- 是否可以输入表达式 -->    </attribute>    <attribute>        <name>var</name>        <required>false</required>        <rtexprvalue>false</rtexprvalue>    </attribute>    <attribute>        <name>outEl</name>        <required>false</required>        <rtexprvalue>true</rtexprvalue>    </attribute>  </tag>  </taglib>

public class NowTimeTag extends TagSupport{    //结束标签后运行doEndTag(),开始解析标签时执行doStartTag()    private String format="yyyy年MM月dd日 hh:mm:ss";    private String var;    private boolean outEl;//  @Override//  public int doEndTag() throws JspException {//      System.out.println("doEndTag");//      return EVAL_PAGE;//  }    @Override    public int doStartTag() throws JspException {        try {        Date date=new Date();        SimpleDateFormat sdf=new SimpleDateFormat(format);        String dateStr=sdf.format(date);        if(var!=null&&outEl){            pageContext.setAttribute(var, dateStr);        }else{            pageContext.getOut().print(dateStr);        }        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return EVAL_BODY_INCLUDE;    }    public String getFormat() {        return format;    }    public void setFormat(String format) {        this.format = format;    }    public String getVar() {        return var;    }    public void setVar(String var) {        this.var = var;    }    public boolean isOutEl() {        return outEl;    }    public void setOutEl(boolean outEl) {        this.outEl = outEl;    }}

PS:

doStartTag()执行在属性输入之后
标签体显示控制：doStartTag()返回值EVAL_BODY_INCLUDE则显示，SKIP_BODY则跳过
doEndTag()控制后续页面是否显示:EVAL_PAGE,SKIP_PAGE

3.extends TagSupport实现for循环自定义标签

    <mytag:for begin="1" end="10" step="1">        a<br>    </mytag:for><br>

public class ForTag extends TagSupport{    private int begin;    private int end;    private int step;    @Override    //在标签体后循环执行    public int doAfterBody() throws JspException {        if(end>=begin){            begin=begin+step;            return EVAL_BODY_AGAIN;        }else{            return EVAL_BODY_INCLUDE;        }    }    @Override    public int doStartTag() throws JspException {        if(end>=begin){            begin=begin+step;            return EVAL_BODY_INCLUDE;        }else{            return SKIP_BODY;        }    }    public int getBegin() {        return begin;    }    public void setBegin(int begin) {        this.begin = begin;    }    public int getEnd() {        return end;    }    public void setEnd(int end) {        this.end = end;    }    public int getStep() {        return step;    }    public void setStep(int step) {        this.step = step;    }}

4.extends BodyTagSupport创建可获取标签提体的自定义标签

    <mytag:newBean var="user" type="com.lps.pojo.Users" scope="request" regex="," >        id:1,userName:李四,age:30    </mytag:newBean>    ${user.id}<br>    ${user.userName }    ${user.age }

public class NewBeanTag extends BodyTagSupport{    private String var;    private String type;    private String regex=",";    private String scope="page";    private Class c;    private Object obj;    @Override    public int doEndTag() throws JspException {        try {            String body=bodyContent.getString().trim();            String fields[]=body.split(regex);            for(String field:fields){                String fieldName=field.split(":")[0];                String fieldValue=field.split(":")[1];                String setMethodName="set"+fieldName.substring(0,1).toUpperCase()+fieldName.substring(1);                String getMethodName="get"+fieldName.substring(0,1).toUpperCase()+fieldName.substring(1);                Method getMethod=c.getMethod(getMethodName, null);                Method setMethod=c.getMethod(setMethodName, getMethod.getReturnType());                if(getMethod.getReturnType()==Integer.class||getMethod.getReturnType()==int.class){                    int num=Integer.parseInt(fieldValue);                    setMethod.invoke(obj, num);                }else{                    setMethod.invoke(obj, fieldValue);                }            }        } catch (NoSuchMethodException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (SecurityException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IllegalAccessException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IllegalArgumentException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (InvocationTargetException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return EVAL_PAGE;    }    @Override    public int doStartTag() throws JspException {        try {            c=Class.forName(type);            obj=c.newInstance();            switch(scope){                case "page":pageContext.setAttribute(var, obj);break;                case "request":pageContext.getRequest().setAttribute(var, obj);break;                case "session":pageContext.getSession().setAttribute(var, obj);break;                case "application":pageContext.getServletContext().setAttribute(var, obj);break;                default:pageContext.setAttribute(var, obj);            }        } catch (ClassNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (InstantiationException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IllegalAccessException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return EVAL_BODY_BUFFERED;    }    public String getVar() {        return var;    }    public void setVar(String var) {        this.var = var;    }    public String getType() {        return type;    }    public void setType(String type) {        this.type = type;    }    public String getRegex() {        return regex;    }    public void setRegex(String regex) {        this.regex = regex;    }    public String getScope() {        return scope;    }    public void setScope(String scope) {        this.scope = scope;    }}

ps:

doStartTag()设置返回值为EVAL_BODY_BUFFERED，将标签体内容放入缓存（内存）
doEndTag()或doAfterBody()中利用父类的bodyContent对象获取标签体内容。

5.extends SimpleTagSupport创建可获取标签提体的自定义标签

重写doTag()方法，没有任何返回值。
属性读取，标签体读取getJspBody()，页面输出或会话区间添加值getJspContext(),PageContext.SESSION_SCOPE

标签体读取getJspBody():

StringWriter sw=new StringWriter();getJspBody().invoke(sw);System.out.println(sw.toString().trim());sb.append(sw.toString());

页面输出或会话区间添加值

        System.out.println(getJspContext().getAttribute("demo"));System.out.println(getJspContext().getAttribute("demo",PageContext.SESSION_SCOPE));getJspContext().setAttribute("demoStr", "李珍基", PageContext.REQUEST_SCOPE);

6.嵌套标签

一般嵌套和普通标签开发无差别，唯一难点——当父标签采用BodyTagSupport并设置EVAL_BODY_BUFFERED时，必须将子表签重新写入父标签输出流，因为此时子标签的输出流不是pageContext.getOut()页面输出流而是父标签的bodyContent对象本身。

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