JavaWeb----自定义标签的开发

最大值标签：

MaxNumberTag.java

package cn.limbo.tags;import javax.servlet.jsp.JspContext;import javax.servlet.jsp.JspException;import javax.servlet.jsp.PageContext;import javax.servlet.jsp.tagext.JspFragment;import javax.servlet.jsp.tagext.JspTag;import javax.servlet.jsp.tagext.SimpleTag;import java.io.IOException;/** * Created by Limbo on 2016/9/21. */public class MaxNumberTag implements SimpleTag{    private String num1;    private String num2;    private PageContext pageContext;    public void setNum1(String num1) {        this.num1 = num1;    }    public void setNum2(String num2) {        this.num2 = num2;    }    @Override    public void doTag() throws JspException, IOException {        Integer num1Integer = Integer.parseInt(num1);        Integer num2Integer = Integer.parseInt(num2);        Integer max = num1Integer > num2Integer ? num1Integer : num2Integer;        this.pageContext.getOut().print("最大的数是： " + max);    }    @Override    public void setParent(JspTag jspTag) {    }    @Override    public JspTag getParent() {        return null;    }    @Override    public void setJspContext(JspContext jspContext) {        this.pageContext = (PageContext) jspContext;    }    @Override    public void setJspBody(JspFragment jspFragment) {    }}

myTag.tld

 <tag>        <name>max</name>        <tag-class>cn.limbo.tags.MaxNumberTag</tag-class>        <body-content>empty</body-content>        <attribute>            <name>num1</name>            <required>true</required>            <rtexprvalue>true</rtexprvalue>        </attribute>        <attribute>            <name>num2</name>            <required>true</required>            <rtexprvalue>true</rtexprvalue>        </attribute>    </tag>

转换大写标签：

ToUpperCaseTag.java

package cn.limbo.tags;import javax.servlet.jsp.JspException;import javax.servlet.jsp.tagext.SimpleTagSupport;import java.io.IOException;import java.io.StringWriter;/** * Created by Limbo on 2016/9/21. */public class ToUpperCaseTag extends SimpleTagSupport {    @Override    public void doTag() throws JspException, IOException {        //获取标签体中的内容        StringWriter sw = new StringWriter();        getJspBody().invoke(sw);  //将标签体中的内容以输出流写入到sw中，如果为null直接输出到屏幕        String content = sw.toString().toUpperCase();//转大写        //输出到页面        getJspContext().getOut().print(content);    }}

myTag.tld

<tag>        <name>uppercase</name>        <tag-class>cn.limbo.tags.ToUpperCaseTag</tag-class>        <body-content>scriptless</body-content>    </tag>

迭代标签：

ForEachTag.java

package cn.limbo.tags;import javax.servlet.jsp.JspException;import javax.servlet.jsp.tagext.SimpleTagSupport;import java.io.IOException;import java.lang.reflect.Array;import java.util.ArrayList;import java.util.Collection;import java.util.Iterator;import java.util.Map;/** * Created by Limbo on 2016/9/21. */public class ForEachTag extends SimpleTagSupport{    private Collection<Object> collection;    private String var;    private Object items;    public void setItems(Object items) {        this.items = items;        //c标签的源码也是这样写的 利用一堆的instanceof来判断传入参数的类型        if(items instanceof Collection)        {            collection = (Collection<Object>) items;        }        if(items instanceof Map)        {            Map map = (Map) items;            collection = map.entrySet();        }        //加上这个就可以使用8种基本类型的迭代        if(items.getClass().isArray()) //这个是最重要的，反射判断        {            this.collection = new ArrayList<>();            int length = Array.getLength(items);            for(int i = 0; i < length; ++i)            {                Object value = Array.get(items,i);                collection.add(value);            }        }    }    public void setVar(String var) {        this.var = var;    }    @Override    public void doTag() throws JspException, IOException {    //遍历items对应的集合        Iterator it = this.collection.iterator();        while(it.hasNext())        {            Object value = it.next();            //把正在遍历的对象放到pageContext中 键：var 值：正在遍历的对象            this.getJspContext().setAttribute(var,value);            //把标签体的内容输出到页面上            this.getJspBody().invoke(null);        }    }}

myTag.tld

<tag>        <name>forEachTag</name>        <tag-class>cn.limbo.tags.ForEachTag</tag-class>        <body-content>JSP</body-content>        <attribute>            <name>items</name>            <required>true</required>            <rtexprvalue>true</rtexprvalue>        </attribute>        <attribute>            <name>var</name>            <required>true</required>            <rtexprvalue>true</rtexprvalue>        </attribute>    </tag>

应用：

<%@ page import="cn.limbo.tags.Customer" %><%@ page import="java.util.List" %><%@ page import="java.util.ArrayList" %><%@ page import="java.util.Map" %><%@ page import="java.util.HashMap" %><%--  Created by IntelliJ IDEA.  User: Limbo  Date: 2016/9/21  Time: 13:56  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %><%@taglib prefix="limbo" uri="http://www.limbo.com/jsp/jstl/core" %><%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %><html><head>    <title>Hello</title></head><body>    <%        List<Customer> customers = new ArrayList<>();        customers.add(new Customer(1,"AA"));        customers.add(new Customer(2,"BB"));        customers.add(new Customer(3,"CC"));        customers.add(new Customer(4,"DD"));        customers.add(new Customer(5,"EE"));        Map<String , List<Customer> > map = new HashMap<>();        map.put("customers",customers);        request.setAttribute("map",map);    %>    <limbo:hello></limbo:hello>    <limbo:max num1="12" num2="17"></limbo:max>    <br><br>    <limbo:forEachTag items="${requestScope.map}" var="cust" >       <limbo:forEachTag items="${cust.value}" var="content">           ID: ${content.id} ---- Name: ${content.name}<br><br>       </limbo:forEachTag>    </limbo:forEachTag>    <limbo:uppercase>hello world</limbo:uppercase>    <%--<c:forEach items="${requestScope.map}" var="cust">--%>        <%--${cust.key} ---- ${cust.value}--%>    <%--</c:forEach>--%></body></html>