上传文件时出现 NullPointerException [英] NullPointerException when uploading a file

问题描述

上传文件时出现以下错误:

<块引用>

Struts 问题报告 Struts 检测到一个未处理的异常:消息:文件:java/io/File.java 行号:317Stacktraces java.lang.NullPointerException java.io.File.(File.java:317)example.uploadFile.execute(uploadFile.java:36)sun.reflect.NativeMethodAccessorImpl.invoke0(本机方法)sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.jav‌ a:43)java.lang.reflect.Method.invoke(Method.java:483)

index.jsp

<label for="myFile">上传您的文件</label><input type="file" name="myFile"/><input type="submit" value="上传"/></表单>

上传文件.java

包示例；导入 java.io.File;导入 org.apache.commons.io.FileUtils;导入 java.io.IOException;导入 com.opensymphony.xwork2.ActionSupport;公共类 uploadFile 扩展 ActionSupport {私人文件 myFile;私人字符串 myFileContentType;私人字符串 myFileFileName;私有字符串destPath；公共字符串执行(){destPath = "C:\Program Files\Apache Software Foundation\Apache Tomcat 8.0.3\work";尝试{System.out.println("源文件名:" + myFile);System.out.println("Dst 文件名:" + myFileFileName);File destFile = new File(destPath, myFileFileName);FileUtils.copyFile(myFile, destFile);}catch(IOException e){返回错误；}返回成功；}公共文件 getMyFile() {返回我的文件；`}public void setMyFile(File myFile) {this.myFile = myFile;这是用户选择上传的文件}公共字符串 getMyFileContentType() {返回 myFileContentType；上传文件的内容类型}public void setMyFileContentType(String myFileContentType) {this.myFileContentType = myFileContentType;`}公共字符串 getMyFileFileName() {返回我的文件文件名；}public void setMyFileFileName(String myFileFileName) {this.myFileFileName = myFileFileName;}}

struts.xml

<include file="example.xml"/><constant name="struts.devMode" value="true"/><constant name="struts.multipart.maxSize" value="1000000"/><!-- 默认包的配置.--><package name="default" extends="struts-default"><action name="upload" class="example.uploadFile"><interceptor-ref name="basicStack"/><interceptor-ref name="fileUpload"><param name="allowedTypes">image/jpeg,image/gif</param></interceptor-ref><result name="success">/success.jsp</result><result name="error">/error.jsp</result></动作></包></支柱>

解决方案

要正常工作，FileUpload 拦截器必须在 basicStack 中的其他一些拦截器之前运行；

您可以在 struts-default.xml:

示例 1:

<!-- 示例文件上传堆栈--><interceptor-stack name="fileUploadStack"><interceptor-ref name="fileUpload"/><interceptor-ref name="basicStack"/></拦截器堆栈>

示例 2:

<interceptor-ref name="异常"/><interceptor-ref name="alias"/><interceptor-ref name="servletConfig"/><interceptor-ref name="i18n"/><interceptor-ref name="prepare"/><interceptor-ref name="chain"/><interceptor-ref name="scopedModelDriven"/><interceptor-ref name="modelDriven"/><interceptor-ref name="fileUpload"/><interceptor-ref name="checkbox"/><interceptor-ref name="datetime"/><interceptor-ref name="multiselect"/><interceptor-ref name="staticParams"/><interceptor-ref name="actionMappingParams"/><interceptor-ref name="params"><param name="excludeParams">^action:.*,^method:.*</param></interceptor-ref><interceptor-ref name="conversionError"/><interceptor-ref name="validation"><param name="excludeMethods">input,back,cancel,browse</param></interceptor-ref><interceptor-ref name="workflow"><param name="excludeMethods">input,back,cancel,browse</param></interceptor-ref><interceptor-ref name="debugging"/><interceptor-ref name="deprecation"/></拦截器堆栈>

然后将其手动放置在 basicStack 声明之前，或使用堆栈(defaultStack 或 fileUploadStack)并包含拦截器的名称在参数名称之前，例如:

<param name="fileUpload.allowedTypes">image/jpeg,image/gif</param></interceptor-ref>

或

<param name="fileUpload.allowedTypes">image/jpeg,image/gif</param></interceptor-ref>

When uploading a file, I get the following error:

Struts Problem Report Struts has detected an unhandled exception: Messages: File: java/io/File.java Line number: 317 
Stacktraces java.lang.NullPointerException java.io.File.(File.java:317) 
    example.uploadFile.execute(uploadFile.java:36) 
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.jav‌​a:43)
    java.lang.reflect.Method.invoke(Method.java:483)

index.jsp

<form action="upload" method="post" enctype="multipart/form-data">
    <label for="myFile">Upload your file</label>
    <input type="file" name="myFile" />
    <input type="submit" value="Upload"/>
</form>

uploadFile.java

package example;
import java.io.File;
import org.apache.commons.io.FileUtils;
import java.io.IOException;    
import com.opensymphony.xwork2.ActionSupport;

public class uploadFile extends ActionSupport {
   private File myFile;
   private String myFileContentType;
   private String myFileFileName;
   private String destPath;

   public String execute() {

      destPath = "C:\Program Files\Apache Software Foundation\Apache Tomcat 8.0.3\work";

      try{
         System.out.println("Src File name: " + myFile);
         System.out.println("Dst File name: " + myFileFileName);                     
         File destFile  = new File(destPath, myFileFileName);
         FileUtils.copyFile(myFile, destFile);      
      }catch(IOException e){
         return ERROR;
      }

      return SUCCESS;
   }

   public File getMyFile() {
      return myFile;`
   }
   public void setMyFile(File myFile) {
      this.myFile = myFile; this the file which user selects to upload
   }
   public String getMyFileContentType() {
      return myFileContentType; content type of the uploading file
   }
   public void setMyFileContentType(String myFileContentType) {
      this.myFileContentType = myFileContentType;`
   }
   public String getMyFileFileName() {
      return myFileFileName;
   }
   public void setMyFileFileName(String myFileFileName) {
      this.myFileFileName = myFileFileName; 
   }
}

struts.xml

<struts>
    <include file="example.xml"/>
    <constant name="struts.devMode" value="true" />
    <constant name="struts.multipart.maxSize" value="1000000" />

    <!-- Configuration for the default package. -->
    <package name="default" extends="struts-default">
       <action name="upload" class="example.uploadFile">
            <interceptor-ref name="basicStack"/>
            <interceptor-ref name="fileUpload">
                <param name="allowedTypes">image/jpeg,image/gif</param>
            </interceptor-ref>
            <result name="success">/success.jsp</result>
            <result name="error">/error.jsp</result>
        </action>
    </package>
</struts>

解决方案

To work properly, the FileUpload Interceptor must run before some other Interceptors in the basicStack;

you can check it out in the struts-default.xml:

Example 1:

<!-- Sample file upload stack -->
<interceptor-stack name="fileUploadStack">
    <interceptor-ref name="fileUpload"/>
    <interceptor-ref name="basicStack"/>
</interceptor-stack>

Example 2:

<interceptor-stack name="defaultStack">
    <interceptor-ref name="exception"/>
    <interceptor-ref name="alias"/>
    <interceptor-ref name="servletConfig"/>
    <interceptor-ref name="i18n"/>
    <interceptor-ref name="prepare"/>
    <interceptor-ref name="chain"/>
    <interceptor-ref name="scopedModelDriven"/>
    <interceptor-ref name="modelDriven"/>
    <interceptor-ref name="fileUpload"/>
    <interceptor-ref name="checkbox"/>
    <interceptor-ref name="datetime"/>
    <interceptor-ref name="multiselect"/>
    <interceptor-ref name="staticParams"/>
    <interceptor-ref name="actionMappingParams"/>
    <interceptor-ref name="params">
        <param name="excludeParams">^action:.*,^method:.*</param>
    </interceptor-ref>
    <interceptor-ref name="conversionError"/>
    <interceptor-ref name="validation">
        <param name="excludeMethods">input,back,cancel,browse</param>
    </interceptor-ref>
    <interceptor-ref name="workflow">
        <param name="excludeMethods">input,back,cancel,browse</param>
    </interceptor-ref>
    <interceptor-ref name="debugging"/>
    <interceptor-ref name="deprecation"/>
</interceptor-stack>

Then place it manually before the basicStack declaration, or use a stack (the defaultStack, or the fileUploadStack) and include the Interceptor's name before the parameter's name, for example:

<interceptor-ref name="defaultStack">
    <param name="fileUpload.allowedTypes">image/jpeg,image/gif</param>
</interceptor-ref>

or

<interceptor-ref name="fileUploadStack">
    <param name="fileUpload.allowedTypes">image/jpeg,image/gif</param>
</interceptor-ref>

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