JavaWeb—自定义标签练习

ゝ一世哀愁。 2023-08-17 17:40 79阅读 0赞

**练习一：<max:num1="" num2=""/>**

**<petrelsky:maxTagDemo num1="23" num2="35">**

**练习二：定制一个带有一个属性的标签<xxx:readFile src="">用于输出指定文件的内容**

**<petrelsky:readFileTagDemo src="WEB-INF/haha.txt">**

**练习一：**

**创建MaxTag类并实现SimpleTag，添加num1、num2属性和setter方法，在doTag()方法中完成比较和输出。**

package com.demo.tag;
    
    import javax.servlet.jsp.JspContext;
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.JspWriter;
    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;
    
    public class MaxTag implements SimpleTag {
        private String num1;
        private String num2;
    
        public void setNum1(String num1) {
            this.num1 = num1;
        }
    
        public void setNum2(String num2) {
            this.num2 = num2;
        }
    
        @Override
        public void doTag() throws JspException, IOException {
            int a = 0;
            int b = 0;
    
            JspWriter out = pageContext.getOut();
    
            try {
                a = Integer.parseInt(num1);
                b = Integer.parseInt(num2);
                out.print(a > b ? a : b);
            }catch (Exception e){
                out.print("输入的属性格式不正确！！！");
            }
    
        }
    
        @Override
        public void setParent(JspTag jspTag) {
    
        }
    
        @Override
        public JspTag getParent() {
            return null;
        }
    
        private PageContext pageContext;
    
        @Override
        public void setJspContext(JspContext jspContext) {
                this.pageContext = (PageContext) jspContext;
        }
    
        @Override
        public void setJspBody(JspFragment jspFragment) {
    
        }
    }

**在mytld.tld中进行标签的相关配置**

<tag>
            <name>max</name>
            <tag-class>com.demo.tag.MaxTag</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>

**在jsp页面引用标签，首先需要导入标签**

<%@taglib prefix="yhs" uri="http://mycompany.com" %>

<yhs:max num1="${param.a}" num2="${param.b}"></yhs:max>

**效果图：**

![1642540-20190713095050963-1701456069.png][]

![1642540-20190713095114361-948295164.png][]

通常情况下开发简单标签直接继承SimpleTagSupport就可以了，可以直接调用其对应的getter方法的到 对应API

public class SimpleTagSupport implements SimpleTag {
        private JspTag parentTag;
        private JspContext jspContext;
        private JspFragment jspBody;
    
    
        public void doTag() throws JspException, IOException {
        }
    
        public void setParent(JspTag parent) {
            this.parentTag = parent;
        }
    
        public JspTag getParent() {
            return this.parentTag;
        }
    
        public void setJspContext(JspContext pc) {
            this.jspContext = pc;
        }
    
        protected JspContext getJspContext() {
            return this.jspContext;
        }
    
        public void setJspBody(JspFragment jspBody) {
            this.jspBody = jspBody;
        }
    
        protected JspFragment getJspBody() {
            return this.jspBody;
        }
    
       
    }

**练习二：**

**创建ReadFileTag类继承SimpleTagSupport类，重写doTag()方法，添加src属性**

package com.demo.tag;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    
    public class ReadFileTag extends SimpleTagSupport {
       //相对于当前web应用的根路径额文件名
        private String src;
    
        public void setSrc(String src) {
            this.src = src;
        }
    
        @Override
        public void doTag() throws JspException, IOException {
            PageContext pageContext = (PageContext) getJspContext();
            InputStream is = pageContext.getServletContext().getResourceAsStream(src);
    
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            String str = null;
            while ((str = reader.readLine())!=null){
                pageContext.getOut().write(str);
                pageContext.getOut().write("<br>");
            }
        }
    }

**在读取时标签必须转换为特定的编码符号**

**str = Pattern.compile("<").matcher(str).replaceAll("&lt");**

**str = Pattern.compile(">").matcher(str).replaceAll("&gt");**

**在mytld.tld中进行标签的相关配置**

<tag>
            <name>readfile</name>
            <tag-class>com.demo.tag.ReadFileTag</tag-class>
            <body-content>empty</body-content>
    
            <attribute>
                <name>src</name>
                <required>true</required>
                <rtexprvalue>true</rtexprvalue>
            </attribute>
        </tag>

**在jsp页面引用标签，首先需要导入标签**

<%@taglib prefix="yhs" uri="http://mycompany.com" %>
     <yhs:readfile src="/WEB-INF/note.txt"></yhs:readfile>

**效果图：**

**![1642540-20190713103546898-1763053616.png][]**

转载于:https://www.cnblogs.com/yangHS/p/11177542.html

[1642540-20190713095050963-1701456069.png]: /images/20230808/f26ab14092e340e7951f6431239e922e.png
[1642540-20190713095114361-948295164.png]: /images/20230808/f2ad8f153e1a43c08cdd5f9fbcc9ffff.png
[1642540-20190713103546898-1763053616.png]: /images/20230808/26c43213a5b24e0f91d6c47950c9ebe7.png