JSP EL 没有找到 requestScope 变量？

Question

所以，我正在尝试学习一些 Spring MVC，我尝试的第一个教程有一个 model.addAttribute("printme", "From spring");，在 JSP 中有一个 ${printme}。

我的控制器很简单：

@RequestMapping(value = "index", method = RequestMethod.GET)
public String index(Model modelMap) {
    System.out.println("on method");
    modelMap.addAttribute("printme", "Hello Spring FROM INDEX !!");
    return "index";
}

当我运行代码不起作用时，我开始添加到 JSP。

我在 body 中结束了这个：

        <h1>
            ${param.printme}
            <br />
            ${printme}
            <br />
            ${requestScope.printme}
            <br />
            <%=request.getParameter("printme")%>
            <br />
            <%=request.getAttribute("printme")%>
            <br />
            <%=pageContext.findAttribute("printme")%>
        </h1>

我的输出源如下所示：

    <h1>

            <br />

            <br />
            Hello Spring FROM INDEX !!
            <br />
            null
            <br />
            Hello Spring FROM INDEX !!
            <br />
            Hello Spring FROM INDEX !!
        </h1>

我希望 param.printme 是空字符串，request.getParameter() 也是空字符串。

不应该 ${printme} 搜索 requestScope 并找到它吗？

${printme} 不应该与

相同

${requestScope.printme}
<%=requestScope.getAttribute("printme")%> 和
<%=pageContext.findAttribute("printme")%>？

这是怎么回事，为什么 ${printme} 找不到属性？

我知道我可以继续使用 ${requestScope.printme}，但它更冗长，我想知道为什么它会这样。

以防万一，我使用的是 Tomcat7.0.52、Spring 4.0 xsds 和 java ee 3.0 xsds。

Answer 1

在我看来，您的 jsp 文件顶部没有引用 jstl。美元符号是 jstl shorthand。确保 jsp 文件的顶部有以下内容。

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>

Answer 2

我有以下简单项目：

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                             http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>biz.tugay</groupId>
    <artifactId>smvcelex</artifactId>
    <packaging>war</packaging>

    <version>1.0-SNAPSHOT</version>
    <name>smvcelex Maven Webapp</name>
    <url>http://maven.apache.org</url>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.el</groupId>
            <artifactId>javax.el-api</artifactId>
            <version>3.0.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>4.0.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>4.0.5.RELEASE</version>
        </dependency>
    </dependencies>

    <build>
        <finalName>smvcelex</finalName>
        <plugins>
            <plugin>
                <groupId>org.eclipse.jetty</groupId>
                <artifactId>jetty-maven-plugin</artifactId>
                <version>9.2.1.v20140609</version>
            </plugin>
        </plugins>
    </build>

    <properties>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

</project>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                             http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0">

    <servlet>
        <servlet-name>springDispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/servletContext.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>springDispatcher</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <jsp-config>
        <jsp-property-group>
            <url-pattern>*.jsp</url-pattern>
            <url-pattern>*.jspf</url-pattern>
            <page-encoding>UTF-8</page-encoding>
            <scripting-invalid>true</scripting-invalid>
            <trim-directive-whitespaces>true</trim-directive-whitespaces>
            <default-content-type>text/html</default-content-type>
        </jsp-property-group>
    </jsp-config>

</web-app>

servletContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans-4.0.xsd">

    <bean id="sampleController" class="biz.tugay.SampleController"/>

    <bean id="viewResolver"
          class="org.springframework.web.servlet.view.InternalResourceViewResolver"/>

</beans>

SampleController.java

package biz.tugay;

/* User: koray@tugay.biz Date: 2016/08/16 */


import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
@RequestMapping(value = "/")
public class SampleController {

    @RequestMapping(value = "", method = RequestMethod.GET)
    public String indexController(Model model) {
        model.addAttribute("printme", "Hello Spring FROM INDEX !!");
        return "index.jsp";
    }
}

最后 index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8"/>
    <title>Hello</title>
</head>
<body>
    ${printme}
</body>
</html>

当我访问localhost:8080时，我会看到文字

Hello Spring FROM INDEX !!

很好..

请将您的项目与本项目进行比较，提供额外的代码并在需要时进一步询问。

JSP EL 没有找到 requestScope 变量？

JSP EL not finding requestScope variable?

spring

jsp

el

spring-mvc