一个可实现任何数据类型的foreach(如List、set、map、各种数组)的foreach自定义标签，用SimpleTagSuppert子类实现
1.定义三个变量,var和items是标签的属性，Collection collection用来临时存储items的一般类型，定义set方法
首先新建实现了SimpleTagSuppert的ForEachTag类
然后定义set方法如下
public void setItems(Object items) {
this.items=items;
if(items instanceof Collection){
collection=(Collection) items;
}
if(items instanceof Map){
Map map=(Map) items;
collection=(map.entrySet());
}
if(items.getClass().isArray()){
collection=new ArrayList();
int length=Array.getLength(items);
for(int i=0;i<length;i++){
collection.add(Array.get(items, i));
}
}
}
public void setVar(String var) {
this.var = var;
}
最后覆盖父类方法doTag方法
@Override
public void doTag() throws JspException, IOException {
Iterator it=this.collection.iterator();
while(it.hasNext()){
Object value=it.next();
this.getJspContext().setAttribute(var, value);
this.getJspBody().invoke(null);
}
}
2.配置tld文件，一个name，两个属性
<tag>
<name>foreach</name>
<tag-class>com.jamsbwo.tag.ForeachTag</tag-class>
<body-content>scriptless</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测试
<body>
<br>----------------------LIST----------------------<br>
<%
List list=new ArrayList();
list.add("aaaaaa");
list.add("BBBBBB");
list.add("cccccc");
list.add("dddddd");
list.add("EEEEEE");
list.add("ffffff");
request.setAttribute("list", list);
%>
<j:foreach items="${list }" var="str">
${str }
</j:foreach>
<br><br>---------------------MAP-----------------------<br>
<%
Map map=new HashMap();
map.put("0", "aaa");
map.put("1", "bbb");
map.put("2", "ccc");
map.put("3", "ddd");
map.put("4", "eee");
map.put("5", "fff");
map.put("6", "ggg");
request.setAttribute("map", map);
%>
<j:foreach items="${map }" var="str">
${str.key }.....${str.value };
</j:foreach>
<br><BR>-------------------------------ARRAY-------------------------------<br>
----------------------INT----------------------<br>
<%
int []inum=new int[]{10,40,54,265};
request.setAttribute("inum", inum);
%>
<j:foreach items="${inum }" var="str">
${str }
</j:foreach>
<br>----------------------BOOLEAN----------------------<br>
<%
boolean [] bnum=new boolean[]{true,true,false,true,false};
request.setAttribute("bnum", bnum);
%>
<j:foreach items="${bnum }" var="str">
${str }
</j:foreach>
<br>----------------------DAOBLE----------------------<br>
<%
double dnum[]=new double[]{1.2,5521.12,54,36.5,8485.5};
request.setAttribute("dnum", dnum);
%>
<j:foreach items="${dnum }" var="str">
${str }
</j:foreach>
</body>
时间： 2024-09-30 05:05:42