实现一个自定义<table>标签

　　需求是有两个自定义的标签<table>和<column>

<table>有个items属性，负责导入数据

package hello;

import java.util.HashMap;
import java.util.Map;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;

public class Column extends TagSupport {
    private String property;
    private String label;

    public int doStartTag() throws JspException {
        if (!(this.getParent() instanceof Table)) {
            throw new JspException("Column must be inside table.");
        }
        Map<String, String> column = new HashMap<String, String>();
        column.put("label", label);
        column.put("property", property);
        Table table = (Table) this.getParent();
        table.getColumns().add(column);
        return SKIP_BODY;
    }

    public int doEndTag() throws JspException {
        return EVAL_PAGE;
    }

    public void setLabel(String label) {
        this.label = label;
    }

    public void setProperty(String property) {
        this.property = property;
    }
}

<column>有property属性负责数据的setter和getter，label负责字段

package hello;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyContent;
import javax.servlet.jsp.tagext.BodyTagSupport;

public class Table extends BodyTagSupport {
    private List<Map<String, String>> columns = new ArrayList<Map<String, String>>();
    private List<Person> personList;
    private String url;

    @Override
    public int doStartTag() throws JspException {
        columns.clear();
        return super.doStartTag();
    }

    @Override
    @SuppressWarnings("unchecked")
    public int doAfterBody() throws JspException {
        try {
            BodyContent bc = this.getBodyContent();
            JspWriter out = bc.getEnclosingWriter();
            HttpServletRequest request = (HttpServletRequest) pageContext
                    .getRequest();
            String orderName = request.getParameter("orderName");
            String orderType = request.getParameter("orderType");
            orderType = "desc".equals(orderType) ? "desc" : "asc";
            out.println("<table id=theObjTable ");
            out.println("class=list_table  border=\"3\";>");
            out.println("<tr class=tr_title>");
            for (int i = 0; i < columns.size(); i++) {
                Map<String, String> column = columns.get(i);
                String label = column.get("label");
                String property = column.get("property");
                label = label == null ? property : label;// 没有列名的用属性做列名
                out.println("<td id='_id_td_" + property + "'>");
                out.println(label);
                out.println("</td>");
            }
            out.println("</tr>");
            if (personList != null) {
                for (int i = 0; i < personList.size(); i++) {
                    out.println("<tr class=tr_data>");
                    Person person = personList.get(i);
                    for (int j = 0; j < columns.size(); j++) {
                        Map<String, String> colmun = columns.get(j);
                        String property = colmun.get("property");
                        String getterStyle = toGetterStyle(property);
                        String method = "get" + getterStyle;
                        try {
                            Method m = person.getClass().getDeclaredMethod(
                                    method);
                            String value = (String) m.invoke(person);
                            out.println("<td>" + value + "</td>");
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        } catch (Exception e) {
        }
        return 0;
    }

    public String toGetterStyle(String column) {
        // TODO Auto-generated method stub
        if (column.length() == 1)
            return column.toUpperCase();
        char ch = column.charAt(0);
        return Character.toUpperCase(ch) + column.substring(1);
    }

    public List<Map<String, String>> getColumns() {
        return this.columns;
    }

    public void setItems(List<Person> personList) {
        this.personList = personList;

    }

}

　　思路：

在<table>设一个List<Map<String, String>> 来存放字段

每个<column>都有一个Map<String, String>存放一个字段，在doEndTag方法中

调用getParent获得<table>对象的getColmun方法获得上面的list，add这个Map

一个循环，把list的字段提出来

一个循环，把column的property加上“get“拼凑方法的字符串，

                            Method m = person.getClass().getDeclaredMethod( method);
                            String value = (String) m.invoke(person);

字符串不能作为方法只能反射调用方法