当jsp的内置标签和jstl标签库内的标签都满足不了需求，这时候就需要开发者自定义标签。

 

自定义标签的开发步骤

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 在你的web应用目录下，找到WEB-INF文件夹，在里面新建一个tld类型的文件

如果你忘记了怎么写，可以参考jstl里的tld文件，如下：

     
         
          
      
       1.0
          
          
      
       1.2
          
          
      
       test
          
          
      
       /zking
          
              
               
       
        yy
               
               
       
        com.TestTag
               
               
       
        jsp
               
               
                   
                    
        
         name
                    
                    
        
         true
                    
                    
        
         false
                
           
      
     

 

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

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

 

自定义set和out标签

分别创建一个·set和out的助手类

1.set

package com.jsp; 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;    }

2.out

package com.jsp;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 {    private static final long serialVersionUID = 5811663341301161566L;    private String value;    public String getValue() {        return value;    }    public void setValue(String value) {        this.value = value;    }    @Override    public int doStartTag() throws JspException {        JspWriter out = pageContext.getOut();        try {            out.print(value);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return SKIP_BODY;    }}

在tld文件中添加set和out的标签

　　
             
      
       set
              
      
       com.jsp.SetTag
              
      
       JSP
              
                  
       
        var
                   
       
        true
                   
       
        false
               
              
                  
       
        value
                   
       
        true
                   
       
        true
               
          
         
             
      
       out
              
      
       com.jsp.OutTag
              
      
       JSP
              
                  
       
        value
                   
       
        true
                   
       
        true
               
          
     

jsp页面演示set，out标签

自定义if标签

步骤同上：

package com.jsp.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    }     }

             
      
       if
              
      
       com.jsp.IfTag
              
      
       JSP
              
                  
       
        test
                   
       
        true
                   
       
        true
               
          
     

 

jsp页面演示：

     
      你看得见我
     
     
      你看不见我
     

定义foreach标签

package com.jsp;/** * foreach助手类 */import java.util.ArrayList;import java.util.Iterator;import java.util.List;import javax.servlet.jsp.JspException;import javax.servlet.jsp.tagext.BodyTagSupport;public class ForeachTag extends BodyTagSupport {    private static final long serialVersionUID = -6290285418914929131L;    private String var;    private List

　　
             
      
       foreah
              
      
       com.jsp.ForeachTag
              
      
       JSP
              
                  
       
        var
                   
       
        true
                   
       
        true
               
              
                  
       
        items
                   
       
        true
                   
       
        true
               
          
     

jsp页面演示foreach标签

<%        List
     
       is = new ArrayList<>();        is.add("aa");        is.add("bb");        is.add("cc");        is.add("dd");        is.add("sb");        pageContext.setAttribute("is", is);    %>     
      
        
                   
        
${i }
        
           
      
     

JSP自定义select标签

创建一个学生类

package com.entity;public class Student {    private String sid;    private String sname;    public String getsid() {        return sid;    }    public void setsid(String sid) {        this.sid = sid;    }    public String getsname() {        return sname;    }    public void setsname(String sname) {        this.sname = sname;    }    public Student(String sid, String sname) {        super();        this.sid = sid;        this.sname = sname;    }    public Student() {        super();        // TODO Auto-generated constructor stub    }    }

 

package com.jsp;import java.io.IOException;import java.lang.reflect.Field;import java.util.ArrayList;import java.util.List;import javax.servlet.jsp.JspException;import javax.servlet.jsp.JspWriter;import javax.servlet.jsp.tagext.BodyTagSupport;import org.apache.commons.beanutils.BeanUtils;public class SelectTag extends BodyTagSupport {    private static final long serialVersionUID = 1L;    private String id;    private String name;    private List

select标签的tld文件

             
      
       select
              
      
       com.jsp.ServletTag
              
      
       JSP
              
                  
       
        id
                   
       
        false
                   
       
        flase
               
              
                  
       
        name
                   
       
        flase
                   
       
        flase
               
              
                  
       
        items
                   
       
        true
                   
       
        true
               
              
                  
       
        textKey
                   
       
        true
                   
       
        false
               
              
                  
       
        textval
                   
       
        true
                   
       
        flase
               
              
                  
       
        headTextKey
                   
       
        false
                   
       
        false
               
              
                  
       
        headTextVal
                   
       
        false
                   
       
        flase
               
              
                  
       
        selectedval
                   
       
        false
                   
       
        true
               
          
     

 

<%    List
     
       student=new ArrayList();    student.add(new Student("1","zs"));    student.add(new Student("2","ls"));    student.add(new Student("3","ww"));    student.add(new Student("4","zl"));    student.add(new Student("5","qq"));    student.add(new Student("6","gd"));    student.add(new Student("7","wb"));    pageContext.setAttribute("stus", student);    %>