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[英]I keep getting this @bean error when trying to run my spring boot app with dynamodb and graphql
[英]Trying to retrieve Spring bean but keep getting a NullPointerException
我正在嘗試從bean檢索BasicDataSource。 每當我嘗試訪問Bean時,我都會收到NullPointerException
我的代碼:
<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1" %>
<%@ page import="java.sql.*" %>
<%@ page import="org.apache.commons.dbcp2.BasicDataSource" %>
<%@ page import="org.postgresql.*" %>
<!DOCTYPE html >
<html xmlns:th="http://www.thymeleaf.org/">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Thank you for suscribing</title>
</head>
<body>
<%
try {
BasicDataSource source = (BasicDataSource)getServletContext().getAttribute("dataSource");
out.write(source.toString());
} catch(Exception e) {
out.write(e.toString());
}
%>
<p>${suscriber.name}<p/>
<p>${suscriber.email}<p/>
</body>
</html>
我的servlet上下文:
<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:beans="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<!-- DispatcherServlet Context: defines this servlet's request-processing infrastructure -->
<!-- Enables the Spring MVC @Controller programming model -->
<annotation-driven />
<!-- Handles HTTP GET requests for /resources/** by efficiently serving up static resources in the ${webappRoot}/resources directory -->
<resources mapping="/resources/**" location="/resources/" />
<!-- Resolves views selected for rendering by @Controllers to .jsp resources in the /WEB-INF/views directory -->
<beans:bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<beans:property name="prefix" value="/WEB-INF/views/" />
<beans:property name="suffix" value=".jsp" />
</beans:bean>
<context:component-scan base-package="com.edutainer4u.site" />
<beans:bean id="dbURL" class="java.net.URI">
<beans:constructor-arg
value="'#{systemEnvironment['DATABASE_URL']}'">
</beans:constructor-arg>
</beans:bean>
<beans:bean id="dataSource"
class="org.apache.commons.dbcp2.BasicDataSource">
<beans:property name="url"
value="jdbc:postgresql://localhost:10000/postgres">
</beans:property>
<beans:property value="blabla"
name="username">
</beans:property>
<beans:property value="blabla"
name="password">
</beans:property>
</beans:bean>
</beans:beans>
無論如何,我一直收到NullPointerException。 我究竟做錯了什么?
您的問題中沒有任何內容表明您已在此處使用的ServletContext
放置了一個名為dataSource
的屬性。
BasicDataSource source = (BasicDataSource)getServletContext().getAttribute("dataSource");
似乎對Servlet API類型ServletContext
和DispatcherServlet
加載的Spring WebApplicationContext
的命名感到困惑, WebApplicationContext
通常也稱為(dispatcher)Servlet上下文。 這是兩個完全不同的組件。
以下是一些相關內容:
使用模型屬性(請求屬性)可能更好。 要從JSP訪問Spring bean,您需要使用適當的屬性名從ServletContext
訪問根WebApplicationContext
或Servlet WebApplicationContext
,這些屬性名稱可能會從Spring的一個版本更改為下一版本,並在該版本上訪問bean。
在視圖解析器配置中,您可以添加需要在JSP中可用的bean列表:
<beans:bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="exposedContextBeanNames">
<list>
<value>dataSource</value>
</list>
</property>
</beans:bean>
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