自定义标签的开发
1.Set,Out标签的开发
2.if标签的开发
3.foreach标签的开发
4.select标签的开发
1.Set,Out标签的开发
首先我们知道Set标签有两个属性一个是var,一个是value
Out标签只有一个属性value
接下来我们来定义他们的助手类
Set助手类
package com.chenkang2;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
public class SetChenkang extends BodyTagSupport {
private static final long serialVersionUID = 1L;
private String var;
private String value;
public String getVar() {
return var;
}
public void setVar(String var) {
this.var = var;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
@Override
public int doStartTag() throws JspException {
pageContext.setAttribute(var, value);
return SKIP_BODY;
}
}
Out助手类
package com.chenkang2;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
public class OutChenkang extends BodyTagSupport {
private static final long serialVersionUID = 1L;
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;
}
}
然后我们来看一下配置的tld文件
<tag>
<name>set</name>
<tag-class>com.chenkang2.SetChenkang</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>var</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>value</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<tag>
<name>out</name>
<tag-class>com.chenkang2.OutChenkang</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>value</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
测试类
<z:set var="sname" value="lalalala"></z:set>
<z:out value="${sname }"></z:out>
测试结果
2.if标签的开发
if只有一个test属性值
助手类
package com.chenkang2;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
public class IfChenkang extends BodyTagSupport{
private static final long serialVersionUID = 1L;
private boolean test;
public boolean isTest() {
return test;
}
public void setTest(boolean test) {
this.test = test;
}
@Override
public int doStartTag() throws JspException {
// TODO Auto-generated method stub
return test?EVAL_BODY_INCLUDE:SKIP_BODY;
}
}
tld配置
<tag>
<name>if</name>
<tag-class>com.chenkang2.IfChenkang</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>test</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
测试类
<z:if test="true">陈康</z:if>
测试结果我就不说了test为true的时候就会显示我的名字
如果定义为false就不会显示
3.foreach标签的开发
首先foreach有var和items两个属性值items则是一个数组
助手类
package com.chenkang2;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
*
* @author 20190528
*
*/
public class ForeachChenkang extends BodyTagSupport {
private static final long serialVersionUID = 1L;
private String var;
private List<Object> items=new ArrayList<>();
public String getVar() {
return var;
}
public void setVar(String var) {
this.var = var;
}
public List<Object> getItems() {
return items;
}
public void setItems(List<Object> items) {
this.items = items;
}
@Override
public int doStartTag() throws JspException {
Iterator<Object> iterator = items.iterator();
// 第一次默认指针存放的位置是没有指向对象的，现在需要指向对象，那么需要指针下移
pageContext.setAttribute(var, iterator.next());
// 因为集合中元素较多，那么指针需要循环的向下移，那么我们需要将迭代器保存，用于下一次指针下移所用
pageContext.setAttribute("iterator", iterator);
return EVAL_BODY_INCLUDE;
}
@Override
public int doAfterBody() throws JspException {
Iterator<Object> iterator = (Iterator<Object>) pageContext.getAttribute("iterator");
// 获取已经保存了的迭代器
if(iterator.hasNext()) {
// 指针下移指向新的元素
pageContext.setAttribute(var, iterator.next());
// 再保存正在使用的迭代器
pageContext.setAttribute("iterator", iterator);
return EVAL_BODY_AGAIN;
}else {
return EVAL_PAGE;
}
}
}
这里要记住的重点就是var是指针不是对象！！！！
tld配置
<tag>
<name>foreach</name>
<tag-class>com.chenkang2.ForeachChenkang</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>
测试
<%
List list=new ArrayList();
list.add(new Stu("001","chenkang"));
list.add(new Stu("002","chenbaba"));
list.add(new Stu("003","dabiaoguo"));
request.setAttribute("list", list);
%>
<br>
<z:foreach items="${list}" var="stu">
${stu.sid},${stu.sname}
</z:foreach>
这里新建一个实体类加数据的类我就不展示了
直接来看测试结果
select标签的开发
助手类
package com.chenkang2;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
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;
/**
* <select id='' name=''>
* <option value='-1' selected>==请选择=</option>
* </select>
* 查询维度：下拉列表
* 修改页面：下拉列表 数据回显
*
* 1.id,name
* 2.数据源items，存入数据库中的testKey,展示列testVal
* 3.加入属性（默认的头部属性值，默认的展示列值）
* 4.加入属性，能够实现数据回显的功能selectedVal;
* @author 20190528
*
*/
public class SelectChenkang extends BodyTagSupport{
private static final long serialVersionUID = 1L;
private String id;
private String name;
private List<Object>items=new ArrayList<Object>();
private String testKey;
private String testVal;
private String headTextKey;
private String headTextVal;
private String 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 List<Object> getItems() {
return items;
}
public void setItems(List<Object> items) {
this.items = items;
}
public String getTestKey() {
return testKey;
}
public void setTestKey(String testKey) {
this.testKey = testKey;
}
public String getTestVal() {
return testVal;
}
public void setTestVal(String testVal) {
this.testVal = testVal;
}
public String getHeadTextKey() {
return headTextKey;
}
public void setHeadTextKey(String headTextKey) {
this.headTextKey = headTextKey;
}
public String getHeadTextVal() {
return headTextVal;
}
public void setHeadTextVal(String headTextVal) {
this.headTextVal = headTextVal;
}
public String getSelectedVal() {
return selectedVal;
}
public void setSelectedVal(String selectedVal) {
this.selectedVal = selectedVal;
}
@Override
public int doStartTag() throws JspException {
// TODO Auto-generated method stub
JspWriter out = pageContext.getOut();
try {
out.print(toHTML());
} catch (IOException | NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return super.doStartTag();
}
/**
* 拼接出下拉列表所对应的的select的html代码
* <select id='' name=''>
* <option value='-1' selected>==请选择=</option>
* </select>
* @return
* @throws SecurityException
* @throws NoSuchFieldException
* @throws IllegalAccessException
* @throws IllegalArgumentException
* @throws NoSuchMethodException
* @throws InvocationTargetException
*/
private StringBuilder toHTML() throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, NoSuchMethodException {
// TODO Auto-generated method stub
StringBuilder sb=new StringBuilder();
sb.append("<select id='"+id+"' name='"+name+"'>");
if(!(headTextKey==null || "".equals(headTextKey) || headTextVal==null || "".equals(headTextVal))) {
sb.append("<option value='"+headTextKey+"' selected>"+headTextVal+"</option>");
}
for (Object obj : items) {
// 要让学生的id存入数据库，让学生的名字展示在jsp页面
// <option value='s00i' selected>zs</option>
// obj sid name
Field field = obj.getClass().getDeclaredField(testKey);
field.setAccessible(true);
String val=(String) field.get(obj);
String html=BeanUtils.getProperty(obj, testVal);
if(val.equals(selectedVal)) {
sb.append("<option value='"+val+"' selected >"+html+"</option>");
}else {
sb.append("<option value='"+val+"' >"+html+"</option>");
}
}
sb.append("</select>");
return sb;
}
}
tld配置
<tag>
<name>select</name>
<tag-class>com.chenkang2.SelectChenkang</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>id</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>name</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>items</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>testKey</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>testVal</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>headTextKey</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>headTextVal</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>selectedVal</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
测试
<z:select headTextKey="-1" headTextVal="==请选择=" items="${list}" testVal="sname" testKey="sid" selectedVal="002"></z:select>
测试结果
哪里修改绑定值了！！！
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