Java 如何在 JSP 中循环遍历 HashMap？
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How to loop through a HashMap in JSP?
提问by blub
How can I loop through a HashMapin JSP?
如何循环遍历HashMapJSP 中的 a？
<%
HashMap<String, String> countries = MainUtils.getCountries(l);
%>
<select name="country">
<%
// Here I need to loop through countries.
%>
</select>
回答by Jim Garrison
Depending on what you want to accomplish within the loop, iterate over one of these instead:
根据您想要在循环中完成的内容，请迭代其中之一：
countries.keySet()countries.entrySet()countries.values()
countries.keySet()countries.entrySet()countries.values()
回答by BalusC
Just the same way as you would do in normal Java code.
就像您在普通 Java 代码中所做的那样。
for (Map.Entry<String, String> entry : countries.entrySet()) {
String key = entry.getKey();
String value = entry.getValue();
// ...
}
However, scriptlets(raw Java code in JSP files, those <% %>things) are considered a poor practice. I recommend to install JSTL(just drop the JAR file in /WEB-INF/liband declare the needed taglibsin top of JSP). It has a <c:forEach>tag which can iterate over among others Maps. Every iteration will give you a Map.Entryback which in turn has getKey()and getValue()methods.
但是，scriptlet（JSP 文件中的原始 Java 代码，那些<% %>东西）被认为是一种糟糕的做法。我建议安装JSTL（只需将 JAR 文件放入/WEB-INF/lib并在 JSP 顶部声明所需的标签库）。它有一个<c:forEach>可以迭代的标签Map。每次迭代都会给你一个Map.Entry返回，它反过来有getKey()和getValue()方法。
Here's a basic example:
这是一个基本示例：
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:forEach items="${map}" var="entry">
Key = ${entry.key}, value = ${entry.value}<br>
</c:forEach>
Thus your particular issue can be solved as follows:
因此，您的特定问题可以按如下方式解决：
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<select name="country">
<c:forEach items="${countries}" var="country">
<option value="${country.key}">${country.value}</option>
</c:forEach>
</select>
You need a Servletor a ServletContextListenerto place the ${countries}in the desired scope. If this list is supposed to be request-based, then use the Servlet's doGet():
您需要 aServlet或 aServletContextListener将 放置${countries}在所需的范围内。如果这个列表应该是基于请求的，那么使用Servlet's doGet()：
protected void doGet(HttpServletRequest request, HttpServletResponse response) {
Map<String, String> countries = MainUtils.getCountries();
request.setAttribute("countries", countries);
request.getRequestDispatcher("/WEB-INF/page.jsp").forward(request, response);
}
Or if this list is supposed to be an application-wide constant, then use ServletContextListener's contextInitialized()so that it will be loaded only once and kept in memory:
或者，如果这个列表应该是一个应用程序范围的常量，那么使用ServletContextListener'scontextInitialized()这样它只会被加载一次并保存在内存中：
public void contextInitialized(ServletContextEvent event) {
Map<String, String> countries = MainUtils.getCountries();
event.getServletContext().setAttribute("countries", countries);
}
In both cases the countrieswill be available in ELby ${countries}.
在这两种情况下，countries将在EL通过${countries}。
Hope this helps.
希望这可以帮助。
See also:
也可以看看：
回答by tk_
Below code works for me
下面的代码对我有用
first I defined the partnerTypesMaplike below in the server side,
首先我partnerTypesMap在服务器端定义如下，
Map<String, String> partnerTypes = new HashMap<>();
after adding values to it I added the object to model,
添加值后，我将对象添加到model，
model.addAttribute("partnerTypesMap", partnerTypes);
When rendering the page I use below foreachto print them one by one.
在渲染页面时，我使用下面的方式foreach将它们一一打印。
<c:forEach items="${partnerTypesMap}" var="partnerTypesMap">
<form:option value="${partnerTypesMap['value']}">${partnerTypesMap['key']}</form:option>
</c:forEach>
