<!-- 在jsp页面中，使用el表达式获取list集合中指定位置的数据 -->
<% 
	Person p1 = new Person();
	p1.setName("name");
	
	Person p2 = new Person();
	p2.setName("name2");
	
	List list = new ArrayList();
	list.add(p1);
	list.add(p2);
	
	request.setAttribute("list",list);
%>

${list[0].name}

<!-- 在jsp页面中，使用el表达式获取map集合的数据 -->
<% 
	Map map = new HashMap();
	map.put("a","aa");
	map.put("b","bb");
	map.put("c","cc");
	
	map.put("1","11");
	
	request.setAttribute("map",map);
%>

${map.a}
<!-- 使用.符号取不到时候使用[]取 -->
${map["1"]} 

package com.xpress.util;
public class Tool {
    public static int add(String num1, String num2) {
        int a = 0;
        int b = 0;
        try {
            a = Integer.parseInt(num1);
            b = Integer.parseInt(num2);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return a+b;
    }
}

public class ViewIPTag implements Tag {
	private PageContext pageContext;
	
	public int doStartTag() throws JspException {
		
		HttpServletRequest request = (HttpServletRequest) pageContext.getRequest();
		JspWriter out = pageContext.getOut();
		
		String ip = request.getRemoteAddr();
    	try {
			out.write(ip);
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
		
		return 0;
	}
	
	public int doEndTag() throws JspException {
		return 0;
	}
	public Tag getParent() {
		return null;
	}
	public void release() {
	}
	public void setPageContext(PageContext arg0) {
		this.pageContext = arg0;
	}
	public void setParent(Tag arg0) {
	}
}

// extends TagSupport
@Override
public int doStartTag() throws JspException {
	return Tag.SKIP_BODY;
}

// extends TagSupport
@Override
public int doEndTag() throws JspException {
	//return Tag.SKIP_PAGE;  //余下jsp不会执行
	return Tag.EVAL_PAGE;
}

// extends TagSupport
int x = 5;

@Override
public int doStartTag() throws JspException {
	return Tag.EVAL_BODY_INCLUDE;
}

@Override
public int doAfterBody() throws JspException {
	x--;
	if(x>0){
		return IterationTag.EVAL_BODY_AGAIN;
	}else{
		return IterationTag.SKIP_BODY;
	}
}

// extends BodyTagSupport 

//bodycontent
@Override
public int doStartTag() throws JspException {
	return BodyTag.EVAL_BODY_BUFFERED;
}

@Override
public int doEndTag() throws JspException {
	//拿到标签体
	String content = this.getBodyContent().getString();
	String result = content.toUpperCase();
	try {
		this.pageContext.getOut().write(result);
	} catch (IOException e) {
		throw new RuntimeException(e);
	}
	return Tag.EVAL_PAGE;
}

// extends SimpleTagSupport
//简单标签使用这个方法完成所有业务逻辑
@Override
public void doTag() throws JspException, IOException {
	//得到代表标签体的JspFragment
	JspFragment jf = this.getJspBody();
	PageContext pageContext = (PageContext) this.getJspContext();
	
	jf.invoke(pageContext.getOut());// 什么都不做则标签体不执行
}

// extends SimpleTagSupport
@Override
public void doTag() throws JspException, IOException {
	throw new SkipPageException();//抛出异常则不执行
}

// 通过属性控制
private int count;  //<xpress:for count="6">

public void setCount(int count) {
	this.count = count;
}

// extends SimpleTagSupport
@Override
public void doTag() throws JspException, IOException {

	for(int i=0;i<count;i++){
		this.getJspBody().invoke(null);
	}
	
}

// extends SimpleTagSupport
@Override
public void doTag() throws JspException, IOException {
	JspFragment jf = this.getJspBody();
	StringWriter sw = new StringWriter();
	jf.invoke(sw);

	String content = sw.getBuffer().toString();
	content = content.toUpperCase();

	PageContext pageContent = (PageContext) this.getJspContext();
	pageContent.getOut().write(content);
}

private int count;  //<xpress:demo5 count="6">
public void setCount(int count) {
	this.count = count;
}
@Override
public void doTag() throws JspException, IOException {
	for(int i=0;i<count;i++){
		this.getJspBody().invoke(null);
	}
}