JSP tag case

Catalog

One 、 Customize foreach label

Two 、 Customize select label

3、 ... and 、 expand ： Customize checkbox label

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One 、 Customize foreach label

foreach Tags can be used to verify what I shared yesterday Jsp The second and third routes in the tag article

Let's review these three routes again ：

JSP There are three routes in the tag life cycle ：
1、 Route one ：doStartTag---> The return value is （SkipBody）--->doEndTag
2、 Route two ： Route two ：doStartTag---> The return value is （EAVL_BODY_INCLUDE）---       >doAfterBody---> The return value is （EAVL_PAGE）--->doEndTag
3、 Route three :doStartTag---> The return value is （EAVL_BODY_INCLUDE）--->doAfterbody---> Return value （EAVL_Body_Again）--->doAfterBody( loop )--->doEndTag
 

1、 Create helper class

package com.zjy.tag;

import java.util.Iterator;
import java.util.List;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * foreach Label helper class 
 * @author  Zhu Jiayin 
 *
 */
public class ForeachTag extends BodyTagSupport{

	private List<Object> items;
	private String var;
	public List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	public String getVar() {
		return var;
	}
	public void setVar(String var) {
		this.var = var;
	}
	@Override
	public int doStartTag() throws JspException {
		Iterator<Object> it = items.iterator();
		pageContext.setAttribute(var, it.next());
		pageContext.setAttribute("it", it);// Get the current position of the iterator 
		return EVAL_BODY_INCLUDE;
	}
	
	@Override
	public int doAfterBody() throws JspException {
	Iterator<Object> it = items.iterator();
	if(it.hasNext()) {
		pageContext.setAttribute(var, it.next());
		pageContext.setAttribute("it", it);
		return EVAL_BODY_AGAIN;
	}
	
	else {
		return EVAL_PAGE;
	}
	}
}

Route 2 and route 3 have different return values in the label body ,foreach The reason why the tag can verify Route 2 and route 3 at the same time is that when we use iterators to traverse , Make a judgment on the data ,it.hasNext Is there a next value , If so, we will continue to get its value and store it , To perform , The return value is return EVAL_BODY_AGAIN; If not , Then execute the subsequent code, that is, return EVAL_PAGE;

How iterators work ： stay foreach Ergodic time , There is a pointer down one by one to find things , When used for the first time , Save the iterator first , Every time the pointer traverses , To save the position of the pointer

2. establish tld class

 <name>foreach</name>
  
    <tag-class>com.zjy.tag.ForeachTag</tag-class>
    
    <body-content>JSP</body-content>
   <attribute> 
   
        <name>var</name>
       
        <required>true</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute> 
    
     <attribute> 
   
        <name>items</name>
       
        <required>true</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute> 
  </tag>

3、jsp Interface reference

<%
  	List<Theaher> ls = new ArrayList<>();
  	ls.add(new Theaher(1," Big bear "));
	ls.add(new Theaher(2," Two bears "));
  	request.setAttribute("ls", ls);
  %>

<z:foreach items="${ls}" var="a">
	${a.tid}:${a.tname}
	</z:foreach>

Running effect ：

Two 、 Customize select label

effect ： It can reduce the amount of code added, deleted, modified and checked

1、 Helper

The helper class has a total of six properties ,items、textval、textkey、headertextval、headertextkey、selectedval  Corresponding to the data source respectively 、option Content displayed in 、option Medium value、 The default selection 、 Selected by default value And data echo

package com.zjy.tag;

import java.io.IOException;
import java.lang.reflect.Field;
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.PropertyUtils;
/**
 * 1. Omit the process of traversal 
 * <z:select></select>
 * 
 * 2. As data echo , No need to add if Judge , No need to add new code 
 * @author Administrator
 *
 *
 * analysis ：1. Background to traverse --》 data source items
 *2. You need an object attribute to represent the corresponding display content of the drop-down box --》textValue
 *3. You need an object attribute to represent the corresponding... Of the drop-down box value value --》textKey
 *4. The default header option shows the content --》headtextval
 *5. Default header option value --》headtextKey
 *6. Values stored in the database , To facilitate data echo --》selectedVal
 *7.id
 *8.name
 *9.Cssstyle
 */
public class SelectTag extends BodyTagSupport{

	private List<Object> items;
	private String textVal;//teacher Medium name
	private String textKey;
	private String headtextval;
	private String headtextKey;
	private String selectedVal;
	
	
	// Beautification interface 
	private String id;
	private String name;
	private String cssStyle;
	
	
	@Override
	public int doStartTag() throws JspException {
		JspWriter out = pageContext.getOut();
		try {
			out.print(toHTML());
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.doStartTag();
	}
	
	private String toHTML() throws Exception, Exception {
		StringBuffer sb = new StringBuffer();
		sb.append("<select id='"+id+"' name='"+name+"'>");
		if(headtextval!=null && !"".equals(headtextval)) {
			sb.append("<option value='"+headtextKey+"'>"+headtextKey+"</option>");
		}
		for (Object object : items) {
			Field textKeyfield = object.getClass().getDeclaredField(textKey);
			textKeyfield.setAccessible(true);
			Object value = textKeyfield.get(object);// Really show the value of the drop-down box 
			if(selectedVal!=null&&!"".equals(selectedVal)&&selectedVal.equals(value)) {
				sb.append("<option  selected value='"+value+"'>"+PropertyUtils.getProperty(object, textVal)+"</option>");
			}
			sb.append("<option value='"+value+"'>"+PropertyUtils.getProperty(object, textVal)+"</option>");
		}
		sb.append("</select>");
		return sb.toString();
	}
	
	
	
	public List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	public String getTextVal() {
		return textVal;
	}
	public void setTextVal(String textVal) {
		this.textVal = textVal;
	}
	public String getTextKey() {
		return textKey;
	}
	public void setTextKey(String textKey) {
		this.textKey = textKey;
	}
	public String getHeadtextval() {
		return headtextval;
	}
	public void setHeadtextval(String headtextval) {
		this.headtextval = headtextval;
	}
	public String getHeadtextKey() {
		return headtextKey;
	}
	public void setHeadtextKey(String headtextKey) {
		this.headtextKey = headtextKey;
	}
	public String getSelectedVal() {
		return selectedVal;
	}
	public void setSelectedVal(String selectedVal) {
		this.selectedVal = selectedVal;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public SelectTag() {
		// TODO Auto-generated constructor stub
	}

	public SelectTag(List<Object> items, String textVal, String textKey, String headtextval, String headtextKey,
			String selectedVal, String id, String name) {
		super();
		this.items = items;
		this.textVal = textVal;
		this.textKey = textKey;
		this.headtextval = headtextval;
		this.headtextKey = headtextKey;
		this.selectedVal = selectedVal;
		this.id = id;
		this.name = name;
	}

	@Override
	public String toString() {
		return "SelectTag [items=" + items + ", textVal=" + textVal + ", textKey=" + textKey + ", headtextval="
				+ headtextval + ", headtextKey=" + headtextKey + ", selectedVal=" + selectedVal + ", id=" + id
				+ ", name=" + name + "]";
	}
	
	
	
	
}

2、tld class

 <name>select</name>
  
    <tag-class>com.zjy.tag.SelectTag</tag-class>
    
    <body-content>JSP</body-content>
    <attribute> 
   
        <name>items</name>
       
        <required>true</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute> 
    
     <attribute> 
   
        <name>textVal</name>
       
        <required>true</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute> 
     <attribute> 
   
        <name>textKey</name>
       
        <required>true</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute> 
     <attribute> 
   
        <name>headerTextVal</name>
       
        <required>false</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute>
     <attribute> 
   
        <name>headerTextKey</name>
       
        <required>false</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute> 
    
    <attribute> 
   
        <name>selectedVal</name>
       
        <required>false</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute> 
     <attribute> 
   
        <name>id</name>
       
        <required>false</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute>
     <attribute> 
   
        <name>selectedVal</name>
       
        <required>false</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute>  
    
     <attribute> 
   
        <name>id</name>
       
        <required>false</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute>
      
     <attribute> 
   
        <name>name</name>
       
        <required>false</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute>  
  </tag>

3、jsp Interface reference

<z:select   textVal="name" items="${ls}" textKey="value">

You can customize the selector to beautify the label

3、 ... and 、 expand ： Customize checkbox label

In fact, it's the same as the one above select The idea of label implementation is similar , Only when echoing, you have to use the collection to receive , Because we may get more than one value . It can also reduce the amount of code

1. Helper

There are six properties of the helper class items、checknr、checkvalue、checked、id、name Corresponding to the data source respectively 、 The contents of the check box and the value Value and a data echo 、id and input Inside the label name value

package com.zjy.tag;

import java.io.IOException;
import java.io.PrintWriter;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
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.PropertyUtils;

/**
 *  Checkbox helper class 
 * <input type="checkbox" name="hid" value="1"  > dance 
 * <input type="checkbox" name="hid" value="2"  > Sing a song 
 * <input type="checkbox" name="hid" value="3"  > read 
 * @author  Zhu Jiayin 
 *
 */
public class CheckedTag extends BodyTagSupport{

	private List<Object> items;
	private String checknr;
	private String checkvalue;
	private  List<Object>  checked;
	// Beautify the selector of the label 
	private String id;
	private String name;
	private Object obj;
	public List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	public String getChecknr() {
		return checknr;
	}
	public void setChecknr(String checknr) {
		this.checknr = checknr;
	}
	public String getCheckvalue() {
		return checkvalue;
	}
	public void setCheckvalue(String checkvalue) {
		this.checkvalue = checkvalue;
	}
	public  List<Object>  getChecked() {
		return checked;
	}
	public void setChecked( List<Object>  checked) {
		this.checked = checked;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public CheckedTag() {
		// TODO Auto-generated constructor stub
	}
	
	public CheckedTag(List<Object> items, String checknr, String checkvalue, List<Object> checked, String id,
			String name, Object obj) {
		this.items = items;
		this.checknr = checknr;
		this.checkvalue = checkvalue;
		this.checked = checked;
		this.id = id;
		this.name = name;
		this.obj = obj;
	}
	@Override
	public int doStartTag() throws JspException {
		JspWriter out = pageContext.getOut();
		try {
			out.print(toHTML());
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.doStartTag();
	}
	private String toHTML() throws Exception{
		StringBuffer sb = new StringBuffer();
		for (Object obj : items) {
			Field Field = obj.getClass().getDeclaredField(checkvalue);
			 Field.setAccessible(true);
			 Object value = Field.get(obj);
			if(checked.contains(value)) {
				sb.append("<input checked type='checkbox' id='"+id+"' name='"+name+"' value='"+value+"'>"+PropertyUtils.getProperty(obj, checknr));
			}
			else {
				sb.append("<input  type='checkbox' id='"+id+"' name='"+name+"' value='"+value+"'>"+PropertyUtils.getProperty(obj, checknr));
			}
		}
		return sb.toString();
	}
	
	
}

2、tld class

<tag>
<!--     Name of tag library  --> 
   <name>checkbox</name>
  
    <tag-class>com.zjy.tag.CheckedTag</tag-class>
    
    <body-content>JSP</body-content>
  <attribute> 
   
        <name>items</name>
       
        <required>true</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute> 
     <attribute> 
   
        <name>checknr</name>
       
        <required>true</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute> 
    
     <attribute> 
   
        <name>checkvalue</name>
       
        <required>true</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute> 
     <attribute> 
   
        <name>checked</name>
       
        <required>true</required>
       
        <rtexprvalue>true</rtexprvalue>
        
        
    </attribute> 
      <attribute> 
   
        <name>id</name>
       
        <required>false</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute> 
     <attribute> 
   
        <name>name</name>
       
        <required>false</required>
       
        <rtexprvalue>false</rtexprvalue>
        
        
    </attribute> 
    
  </tag>
  

3、jsp Page references

Because the data is echoed with sets , So in addition to defining a set of teachers , You also need to define a set

<%
  	List<Theaher> ls = new ArrayList<>();
  	ls.add(new Theaher(1," Big bear "));
	ls.add(new Theaher(2," Two bears "));
  	request.setAttribute("ls", ls);
  	
  	
  	List<Object> list = new ArrayList<>();
  	list.add(1);
  	request.setAttribute("list", list);
  %>

<z:checkbox items="${ls}" checked="${list}" checkvalue="tid" checknr="tname"></z:checkbox>

Effect display ：

Well, let's share it here first  bye~~~~