如何从JSP页面访问环境变量 [英] How to access environment variables from JSP page

问题描述

如何从JSP页面访问环境变量？其中一个隐式对象是否允许访问它们？我找不到解决这个具体问题的例子。理想情况下，我正在寻找类似的东西：

 < c：set var =where值= $ {myEnvironment.machineName} > 
  

解决方案

您可以在服务器启动时读取属性文件 - 使用

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如果您正在寻找样本代码然后在这里找到它。请在下面的帖子中找到它。它可能对你有帮助。

• 在两个jsp与jstl之间获取值




• < a href =http://www.tutorialspoint.com/jsp/jsp_standard_tag_library.htm =nofollow noreferrer> JSP - 标准标签库（JSTL）教程

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其他范围内的更多样本。

 <％ - 设置范围变量 - ％> 
< c：set var =paravalue =$ {41 + 1}scope =page/> 
< c：set var =paravalue =$ {41 + 1}scope =request/> 
< c：set var =paravalue =$ {41 + 1}scope =session/> 
< c：set var =paravalue =$ {41 + 1}scope =application/> 
 
<％ - 打印值 - ％> 
< c：out value =$ {pageScope.para}/> 
< c：out value =$ {requestScope.para}/> 
< c：out value =$ {sessionScope.para}/> 
< c：out value =$ {applicationScope.para}/> 
  

在您的情况下，您已设置属性其中默认页面范围。

How can I access environment variables from a JSP page? Does one of the implicit objects give access to them? I couldn't find an example addressing this specific issue. Ideally I'm looking for something like:

<c:set var="where" value="${myEnvironment.machineName}">

解决方案

You can read the properties file at the server start-up using ServletContextListener and store it as application scoped attribute to access it from anywhere in the application.

Steps to follow:

.properties:

machineName=xyz

web.xml:

<listener>
    <listener-class>com.x.y.z.AppServletContextListener</listener-class>
</listener>

AppServletContextListener.java:

public class AppServletContextListener implements ServletContextListener {

    private static Properties properties = new Properties();

    static {
        // load properties file
        try {
            // absolute path on server outside the war 
            // where properties files are stored

            String absolutePath = ..; 
            File file = new File(absolutePath);
            properties.load(new FileInputStream(file));
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        servletContextEvent.getServletContext().
                                    setAttribute("myEnvironment", properties);
    }
}

JSP:

Then you can just treat it as Map in EL.

${myEnvironment['machineName']}

or

${myEnvironment.machineName}

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Read more about JSTL Core c:set Tag

The <c:set> tag is JSTL-friendly version of the setProperty action. The tag is helpful because it evaluates an expression and uses the results to set a value of a JavaBean or a java.util.Map object.

The <c:set> tag has following attributes:

If target is specified, property must also be specified.

Read more about it HERE

---

If you are looking for sample code then find it here. Please find it at below posts. It might help you.

• Acces value between two jsp with jstl

• JSP - Standard Tag Library (JSTL) Tutorial

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More samples on other scopes.

    <%-- Set scoped variables --%>
    <c:set var="para" value="${41+1}" scope="page" />
    <c:set var="para" value="${41+1}" scope="request" />
    <c:set var="para" value="${41+1}" scope="session" />
    <c:set var="para" value="${41+1}" scope="application" />

    <%-- Print the values --%>
    <c:out value="${pageScope.para}" />
    <c:out value="${requestScope.para}" />
    <c:out value="${sessionScope.para}" />
    <c:out value="${applicationScope.para}" />

In your case you have set an attribute where in default page scope.

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