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JSP tag case
2022-07-28 23:30:00 【I love coriander TVT】
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3、 ... and 、 expand ： Customize checkbox label
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~~~~
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