Question

我有以下代码，它应该返回0到n-1之间的m个数字的排序列表。我已经验证列表已创建更正，但JSP没有打印任何内容。谁能帮我这个？这是我的动作类中的方法。

public static SortedSet<Integer> createCombo(int items, int maxNum) {
    if (items > maxNum) {
        System.out
                .println("Cannot create a combination longer than the highest possible number.");
        return null;
    }

    for (int i = 1; i <= items; i++) {
        int newNum = 0;
        boolean distinctNumber = false;
        while (! distinctNumber) {
            newNum = (int) Math.floor(Math.random() * maxNum);
            distinctNumber = true;

            if (i > 1) {
                Iterator<Integer> iterator = combo.iterator();
                while ((iterator.hasNext()) && (distinctNumber)) {
                    if (newNum == iterator.next()) {
                        distinctNumber = false;
                    }
                }
            }
        }
        combo.add(newNum);
    }

    printCombo();
    return combo;
}

这是我的控制器类中的方法。

public String execute() {
    SortedSet<Integer> combo = new TreeSet<Integer>();

    try {
        if ((items == 0) || (maxNum == 0)) {
            return "failure";
        }
        combo = Combo.createCombo(items, maxNum);
        if (combo != null) {
            HttpSession session = (HttpSession) request.getSession();
            session.setAttribute("combo", combo);
        }

        return "success";
    } catch (Exception e) {
    }
    return "failure";
}

这是我的JSP。我的浏览器中只显示h1标签之间的文字。

<%@ page import="java.io.*"%>
<%@ page import="java.util.List"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib prefix="s" uri="/struts-tags"%>
<html>
<head>
<title>Lotto Results</title>
</head>
<body>
<center>
<h1>Lotto Results</h1>
</center>
<s:iterator value="combo">
        <c:forEach var="iterator" items="${combo.iterator}" >
            ${iterator.next}
        </c:forEach>
</s:iterator>
</body>
</html>

Answer 1

combo 应该是您的Action类的属性，您应该有一个返回集合的方法getCombo()。然后将显示值。

参见示例，我有一个名为 Song 的类和一个名为 AlbumInfoAction

的Action

package vaannila;

public class Song {

    private String title;
    private String genre;

    Song(String title, String genre)
    {
        this.title = title;
        this.genre = genre;
    }
    public String getTitle() {
            return title;
    }
    public void setTitle(String title) {
            this.title = title;
    }
    public String getGenre() {
            return genre;
    }
    public void setGenre(String genre) {
            this.genre = genre;
    }
}

package vaannila;

import java.util.ArrayList;
import java.util.List;


public class AlbumInfoAction{

private String title;
private Artist artist;
private static List&lt;Song&gt; songs = new ArrayList&lt;Song&gt;();

    static {
        songs.add(new Song("Thriller","Disco"));
        songs.add(new Song("Beat It","Rock"));
        songs.add(new Song("Billie Jean","Pop"));
    }

    public String populate()
    {
        title = "Thriller";
        artist = new Artist("Michael Jackson","King of pop");
        return "populate";
    }

    public String execute()
    {
        return "success";
    }

    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public Artist getArtist() {
        return artist;
    }
    public void setArtist(Artist artist) {
        this.artist = artist;
    }

    public List&lt;Song&gt; getSongs() {
        return songs;
    }

}

要进行迭代，我应该将歌曲作为动作类的属性，并且应该存在方法 getSongs 。

JSP代码看起来像这样

<table class="songTable">
<tr class="even">
<td><b>Title</b></td>
<td><b>Genre</b></td>
</tr>
<s:iterator value="songs" status="songStatus">
<tr
class="<s:if test="#songStatus.odd == true ">odd</s:if><s:else>even</s:else>">
<td><s:property value="title" /></td>
<td><s:property value="genre" /></td>
</tr>
</s:iterator>
</table>

希望这有帮助。

Answer 2

我已经解决了自己的问题。我删除了s：iterator标记，并在其中保留了迭代循环并将其更改为以下内容，并且这些更改有效。

<c:forEach var="combo" items="${combo}">
    ${combo}
</c:forEach>

JSTL不打印值

2 个答案: