上传文件时发生NullPointerException [英] NullPointerException when uploading a file

问题描述

上传一个文件时，出现如下错误：

lockquote
$ str $ Struts问题报告Struts has检测到未处理的异常：消息：文件：java / io / File.java行号：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 =uploadmethod =postenctype =multipart / form-data> 
< label for =myFile>上传您的文件< / label> 
< input type =filename =myFile/> 
< input type =submitvalue =上传/> 
< / form> 
  

uploadFile.java

  package示例; 
 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; 
私人字符串myFileContentType; 
 private String myFileFileName; 
 private String destPath; 
 
 public String execute（）{
 
 destPath =C：\\Program Files\\Apache Software Foundation\\Apache Tomcat 8.0.3\\ \\\工作; 
 
尝试{
 System.out.println（Src File name：+ myFile）; 
 System.out.println（Dst文件名：+ myFileFileName）; 
文件destFile =新文件（destPath，myFileFileName）; 
 FileUtils.copyFile（myFile，destFile）; 
} catch（IOException e）{
 return ERROR; 
} 
 
返回SUCCESS; 
 
 $ b $ public File getMyFile（）{
 return myFile;`
} 
 public void setMyFile（File myFile）{
 this。 myFile = myFile;这是用户选择上传的文件
} 
 public String getMyFileContentType（）{
 return myFileContentType;上传文件的内容类型
} 
 public void getMyFileContentType（String myFileContentType）{
 this.myFileContentType = myFileContentType;`
} 
 public String getMyFileFileName（）{
返回myFileFileName; 
 
 public void setMyFileFileName（String myFileFileName）{
 this.myFileFileName = myFileFileName; 
 
 
 
 
 $ str $ str 
 
 $ b 
 < struts> 
< include file =example.xml/> 
< constant name =struts.devModevalue =true/> 
< constant name =struts.multipart.maxSizevalue =1000000/> 
 
 <！ -   - 默认包的配置。 - > 
 < action name =uploadclass =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

， FileUpload 拦截器必须在 basicStack 中的其他拦截器之前运行。



你可以在 struts-default.xml ：

$ b 示例1：

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


示例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>输入，返回，取消，浏览< /参数> 
< / interceptor-ref> 
< interceptor-ref name =workflow> 
< param name =excludeMethods>输入，返回，取消，浏览< /参数> 
< / interceptor-ref> 
< interceptor-ref name =debugging/> 
< interceptor-ref name =deprecation/> 
< / interceptor-stack> 
  

然后在 basicStack 声明之前手动，或使用堆栈（ defaultStack 或 fileUploadStack ），并在参数名称之前包含Interceptor的名称例如：
$ b

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


或

 < interceptor-ref name =fileUploadStack> 
< 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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