Question

我尝试使用ServletContext将图像文件上传到/ webapp / foto /上的文件夹照片，但每次我都有NullPointerExceptions

我该如何正确地做到这一点？

这是UploadFile.class，其中NPE在CONTAINER_ROOT变量上升。

@Component
public class UploadFile {

    @Autowired
    HttpServletRequest httpServletRequest;

    private String CONTAINER_ROOT = httpServletRequest.getSession().getServletContext().getRealPath("/");

    private String DIR_NAME = "foto";

    private String UPLOAD_DIR = CONTAINER_ROOT + File.separator + DIR_NAME;

    private Logger logManager = LogManager.getLogger(this.getClass());


    public String getUploadedPath(MultipartFile file) {
        return upload(file);
    }

    private String upload(MultipartFile file) {

        if (!file.isEmpty()) try {
            byte[] bytes = file.getBytes();
            String fileName = file.getOriginalFilename();
            File dir = new File(UPLOAD_DIR);

            if (!dir.exists()) dir.mkdirs();

            File fileOnServer = new File(dir.getAbsolutePath() + File.separator + fileName);
            BufferedOutputStream outputStream = new BufferedOutputStream(new FileOutputStream(fileOnServer));
            outputStream.write(bytes);
            outputStream.close();

            logManager.warn("UPLOADED FILE LOCATION: " + fileOnServer.getAbsolutePath());

            return fileOnServer.getPath();
        }
        catch (IOException e) {
            logManager.error("Error trying to upload file to location, or file is empty!", e.getMessage());
        }
        return null;
    }

}

这就是我在Controller上使用的方式：

Foto savedFoto = this.fotoRepository.save(new Foto(this.uploadFile.getUploadedPath(file), savedImovel));

Stacktrace：

    Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [br.com.agenciadsw.morenoimoveis.util.UploadFile]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:164)
28-Aug-2014 11:02:16.409 WARNING [RMI TCP Connection(2)-127.0.0.1] org.apache.catalina.loader.WebappClassLoader.clearReferencesJdbc The web application [] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1069)
    ... 71 more
Caused by: java.lang.NullPointerException
    at br.com.agenciadsw.morenoimoveis.util.UploadFile.<init>(UploadFile.java:26)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:148)
    ... 73 more

这里web.xml：

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
            http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

    <display-name>MorenoImoveis</display-name>


        <servlet>
            <servlet-name>dispacher</servlet-name>
            <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
            <init-param>
                <param-name>contextClass</param-name>
                <param-value>org.springframework.web.context.support.AnnotationConfigWebApplicationContext</param-value>
            </init-param>
            <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>
                br.com.agenciadsw.morenoimoveis.cfg.PersistenceConfigurer
                br.com.agenciadsw.morenoimoveis.cfg.SecurityConfigurer
                br.com.agenciadsw.morenoimoveis.cfg.WebMvcConfigurer
            </param-value>
        </init-param>
    </servlet>

    <servlet-mapping>
        <servlet-name>dispacher</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    <context-param>
        <param-name>contextClass</param-name>
        <param-value>
            org.springframework.web.context.support.AnnotationConfigWebApplicationContext
        </param-value>
    </context-param>
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
            br.com.agenciadsw.morenoimoveis.cfg.PersistenceConfigurer
            br.com.agenciadsw.morenoimoveis.cfg.SecurityConfigurer
            br.com.agenciadsw.morenoimoveis.cfg.WebMvcConfigurer
        </param-value>
    </context-param>

    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>


    <filter>
        <filter-name>encodingFilter</filter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter
        </filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>encodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

</web-app>

Answer 1

Spring组件的默认范围是singleton，因此bean可能在应用程序启动时初始化，其中不存在servlet请求。尝试将以下注释添加到类中：

@Scope("request")

您可以找到有效的bean范围here

Answer 2

您可以将图片上传到项目外的文件夹中。我对几张图片很有用

try {
            byte[] bytes = file.getBytes();

            // Creating the directory to store file
            File dir = new File(Utils.getFolderStoreImage(request.getSession().getServletContext().getRealPath("/")));
            if (!dir.exists())
                dir.mkdirs();
            // Create the file on server
            serverFile = new File(Utils.getFolderStoreImage(request.getServletContext().getRealPath("/"))+System.currentTimeMillis()+"-"+UUID.randomUUID().toString()+".jpg");
            BufferedOutputStream stream = new BufferedOutputStream(new FileOutputStream(serverFile));
            stream.write(bytes);
            stream.close();
        } catch (Exception e) {
            result.rejectValue("image", "error when upload image");
            return "product/add";
        }

Utils.java

public class Utils {
public static String getFolderStoreImage(String webContentRoot) {
    if (webContentRoot.endsWith("\\")){
        webContentRoot = webContentRoot.substring(0,webContentRoot.length() - 1);
        }
    String folder = webContentRoot.substring(0, webContentRoot.lastIndexOf("\\") + 1) + "upload\\";
    return folder;
}

}

Answer 3

此代码可帮助您上传任意数量的文件。这里的MultipartFile是包org.springframework.web.multipart.MultipartFile的接口;

 String uploadsDir = "/uploads/";
            String realPathtoUploads = request.getSession().getServletContext().getRealPath(uploadsDir);

            if (!new File(realPathtoUploads).exists()) {
                new File(realPathtoUploads).mkdir();
            }

            List<MultipartFile> files = upload.getFiles();

            List<String> fileNames = new ArrayList<String>();
            try {
                if (files != null && files.size() > 0) {
                    for (MultipartFile file : files) {
                        String fileName = file.getOriginalFilename();
                        String filePath = realPathtoUploads + File.separator + fileName;

                        File destination = new File(filePath);
                        file.transferTo(destination);
                        fileNames.add(fileName);


                    }
                }
            } catch (IllegalStateException e) {
                e.printStackTrace();
                isSuccess = false;
                logger.error("Error : ", e);
            }

如何在webapp文件夹中上传图片

3 个答案: