日向博客最近在优化，有这一样一个小问题,我希望在下面的消息中心页面，未读的消息链接显示蓝色，已读的消息显示红色：
这就需要用jstl做一个判断。
之前的代码是这种形式：
消息中心：<br>
<c:forEach items="${msgPage.content}" begin="0" end="15" step="1" var="msg">
<!-- 如果消息类型为评论 -->
<div id="msg_line">
<c:choose>
<c:when test="${empty msg.sender.username}">
一名游客在${fn:substring(msg.date,0,16)}评论了你的文章<a href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:when>
<c:otherwise>
用户 ${msg.sender.username}在${fn:substring(msg.date,0,16)}评论了你的文章<a href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:otherwise>
</c:choose>
</div>
</c:forEach>
msg.content是后台传来的Message对象的List。遍历显示在页面。
Message实体类的代码：
package sonn.entity; import java.util.Date; import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne; import sonn.enums.MsgIsRead;
import sonn.enums.MsgType; /**
* @ClassName: Message
* @Description: entity class of message
* @author sonne
* @date 2016-12-23 20:32:16
* @version 1.0
*/
@Entity
public class Message { /*id*/
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id; private String content; @OneToOne(fetch = FetchType.EAGER)
private User sender; @OneToOne(fetch = FetchType.EAGER)
private User reciever; private MsgType type; private MsgIsRead is_read; private Date date; @OneToOne(fetch = FetchType.EAGER)
private Article article; public int getId() {
return id;
} public void setId(int id) {
this.id = id;
} public String getContent() {
return content;
} public void setContent(String content) {
this.content = content;
} public User getSender() {
return sender;
} public void setSender(User sender) {
this.sender = sender;
} public User getReciever() {
return reciever;
} public void setReciever(User reciever) {
this.reciever = reciever;
} public MsgType getType() {
return type;
} public void setType(MsgType type) {
this.type = type;
} public Date getDate() {
return date;
} public void setDate(Date date) {
this.date = date;
} public Article getArticle() {
return article;
} public void setArticle(Article article) {
this.article = article;
} public MsgIsRead getIs_read() {
return is_read;
} public void setIs_read(MsgIsRead is_read) {
this.is_read = is_read;
} }
我需要的是根据enum字段is_read来判断是否已读。
package sonn.enums;
public enum MsgIsRead {
Yes, No;
}
于是我最初写下下面的代码：
<%@ page import="sonn.enums.MsgIsRead" %>
.............................
<c:choose>
<c:when test="${empty msg.sender.username}">
<c:choose>
<c:when test="${msg.is_read eq MsgIsRead.No}">
一名游客在${fn:substring(msg.date,0,16)}评论了你的文章<a style="color:red" href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:when>
<c:otherwise>
一名游客在${fn:substring(msg.date,0,16)}评论了你的文章<a href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:otherwise>
</c:choose>
</c:when>
<c:otherwise>
<c:choose>
<c:when test="${msg.is_read eq MsgIsRead.No}">
用户 ${msg.sender.username}在${fn:substring(msg.date,0,16)}评论了你的文章<a style="color:red" href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:when>
<c:otherwise>
用户 ${msg.sender.username}在${fn:substring(msg.date,0,16)}评论了你的文章<a href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:otherwise>
</c:choose>
</c:otherwise>
</c:choose>
上面代码是没有效果的，我以为页面最上方引入了<%@ page import="sonn.enums.MsgIsRead" %>的话，jstl标签就可以获取这个enum对象了。
实际上，jstl标签获取变量的范围只是pageScope, sessionScope, requestScope, applicationScope……
所以，为了获取这个enum需要在判断前先set一下：
<%@ page import="sonn.enums.MsgIsRead" %>
..........................................................................................
消息中心：<br>
<c:set var="Not_Read" value="<%=MsgIsRead.No%>"/>
<c:forEach items="${msgPage.content}" begin="0" end="15" step="1" var="msg">
<!-- 如果消息类型为评论 -->
<div id="msg_line">
<c:choose>
<c:when test="${empty msg.sender.username}">
<c:choose>
<c:when test="${msg.is_read eq Not_Read}">
一名游客在${fn:substring(msg.date,0,16)}评论了你的文章<a style="color:red" href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:when>
<c:otherwise>
一名游客在${fn:substring(msg.date,0,16)}评论了你的文章<a href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:otherwise>
</c:choose>
</c:when>
<c:otherwise>
<c:choose>
<c:when test="${msg.is_read eq Not_Read}">
用户 ${msg.sender.username}在${fn:substring(msg.date,0,16)}评论了你的文章<a style="color:red" href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:when>
<c:otherwise>
用户 ${msg.sender.username}在${fn:substring(msg.date,0,16)}评论了你的文章<a href="/RiXiang_blog/msg/show.form?id=${msg.id}">${msg.article.title}</a><br>
</c:otherwise>
</c:choose>
</c:otherwise>
</c:choose>
</div>
</c:forEach>
<c:set var="Not_Read" value="<%=MsgIsRead.No%>"/>先这样写，jstl才能获取到该java对象~