如何从Jersey的多部分表单中读取多个具有相同名称的（文件）输入？

问题描述

我已经成功开发了一项服务，在该服务中，我阅读了在泽西岛以多部分形式上传的文件。这是我一直在做的非常简化的版本：

  
我已经找到了解决方案，按照下面的例子 FormDataMultipart 。事实证明我非常接近答案。 
 $ b 
  FormDataBodyPart 类提供了一种方法，允许其用户读取值为 InputStream （或理论上，任何其他类，为其提供消息正文阅读器） 
 
 
这是最终的解决方案： 
 
 
表格
 
 
 
表格保持不变。我有几个同名的字段，我可以在其中放置文件。可以同时使用表单输入（当从一个目录上传许多文件时需要这些）以及多个共享名称的输入（灵活的方式从不同位置上传未指定数量的文件）。 
 < form action =/ filesmethod =post也可以在表单中附加更多的输入。 enctype =multipart / form-data> 
< fieldset> 
<图例>同名的多个输入< / legend> 
< input type =filename =testmultiple =multiple/> 
< input type =filename =test/> 
< input type =filename =test/> 
< / fieldset> 
< input type =submitvalue =上传它/> 
< / form> 
  
 
 
 
服务 - 使用 
 
 
 
以下是从多部分表单读取文件集合的简化方法。所有具有相同输入的输入都分配给一个 List ，并且它们的值使用方法。一旦你将这些文件作为 InputStream 实例，就很容易对它们做任何事情。 
  @POST 
 @Path（files）
 @Consumes（MediaType.MULTIPART_FORM_DATA）
 public response uploadMultipart（FormDataMultiPart multiPart）throws IOException {
 List< FormDataBodyPart> fields = multiPart.getFields（test）; （FormDataBodyPart field：fields）
 {
 handleInputStream（field.getValueAs（InputStream.class））; 
} 
 //准备响应
} 
 
 private void handleInputStream（InputStream is）{
 //以任何方式读取流
} 
  
 
I have successfully developed a service, in which I read files uploaded in a multipart form in Jersey. Here's an extremely simplified version of what I've been doing:
@POST
@Path("FileCollection")
@Consumes(MediaType.MULTIPART_FORM_DATA)
public Response uploadFile(@FormDataParam("file") InputStream uploadedInputStream,
        @FormDataParam("file") FormDataContentDisposition fileDetail) throws IOException {
    //handle the file
}
This works just fine but I've been given a new requirement. In addition to the file I'm uploading, I have to handle an arbitrary number of resources. Let's assume these are image files.
I figured I'd just provide the client with a form with one input for the file, one input for the first image and a button to allow adding more inputs to the form (using AJAX or simply plain JavaScript).
<form action="blahblahblah" method="post" enctype="multipart/form-data">
   <input type="file" name="file" />
   <input type="file" name="image" />
   <input type="button" value="add another image" />
   <input type="submit"  />
</form>
So the user can append the form with more inputs for images, like this:
<form action="blahblahblah" method="post" enctype="multipart/form-data">
   <input type="file" name="file" />
   <input type="file" name="image" />
   <input type="file" name="image" />
   <input type="file" name="image" />
   <input type="button" value="add another image" />
   <input type="submit"  />
</form>
I hoped it would be simple enough to read the fields with the same name as a collection. I've done it successfully with text inputs in MVC .NET and I thought it wouldn't be harder in Jersey. It turns out I was wrong.
Having found no tutorials on the subject, I started experimenting. 
In order to see how to do it, I dumbed the problem down to simple text inputs.
<form action="blahblabhblah" method="post" enctype="multipart/form-data">
   <fieldset>
       <legend>Multiple inputs with the same name</legend>
       <input type="text" name="test" />
       <input type="text" name="test" />
       <input type="text" name="test" />
       <input type="text" name="test" />
       <input type="submit" value="Upload It" />
   </fieldset>
</form>
Obviously, I needed to have some sort of collection as a parameter to my method. Here's what I tried, grouped by collection type.
Array
At first, I checked whether Jersey was smart enough to handle a simple array:
@POST
@Path("FileCollection")
@Consumes(MediaType.MULTIPART_FORM_DATA)
public Response uploadFile(@FormDataParam("test") String[] inputs) {
    //handle the request
}
but the array wasn't injected as expected.
MultiValuedMap
Having failed miserably, I remembered that MultiValuedMap objects could be handled out of the box. 
@POST
@Path("FileCollection")
@Consumes(MediaType.MULTIPART_FORM_DATA)
public Response uploadFile(MultiValuedMap<String, String> formData) {
    //handle the request
}
but it doesn't work either. This time, I got an exception
SEVERE: A message body reader for Java class javax.ws.rs.core.MultivaluedMap,
and Java type javax.ws.rs.core.MultivaluedMap<java.lang.String, java.lang.String>,
and MIME media type multipart/form-data;
boundary=----WebKitFormBoundaryxgxeXiWk62fcLALU was not found.
I was told that this exception could be gotten rid of by including the mimepull library so I added the following dependency to my pom:
    <dependency>
        <groupId>org.jvnet</groupId>
        <artifactId>mimepull</artifactId>
        <version>1.3</version>
    </dependency>
Unfortunately the problem persists. It's probably a matter of choosing the right body reader and using different parameters for the generic. I'm not sure how to do this. I want to consume both file and text inputs, as well as some others (mostly Long values and custom parameter classes).
FormDataMultipart
After some more research, I found the FormDataMultiPart class. I've successfully used it to extract the string values from my form
@POST
@Path("upload2")
@Consumes(MediaType.MULTIPART_FORM_DATA)
public Response uploadMultipart(FormDataMultiPart multiPart){
    List<FormDataBodyPart> fields = multiPart.getFields("test");
    System.out.println("Name\tValue");
    for(FormDataBodyPart field : fields){
        System.out.println(field.getName() + "\t" + field.getValue());
        //handle the values
    }
    //prepare the response
}
The problem is, this is a solution to the simplified version of my problem. While I know that every single parameter injected by Jersey is created by parsing a string at some point (no wonder, it's HTTP after all) and I have some experience writing my own parameter classes, I don't really how to convert these fields to InputStream or File instances for further processing.
Therefore, before diving into Jersey source code to see how these objects are created, I decided to ask here whether there is an easier way to read a set (of unknown size) of files. Do you know how to solve this conundrum?
 解决方案 
I have found the solution by following the example with FormDataMultipart. It turns out I was very close to the answer.
The FormDataBodyPart class provides a method that allows its user to read the value as InputStream (or theoretically, any other class, for which a message body reader is present).
Here's the final solution:
Form
The form remains unchanged. I have a couple of fields with the same name, in which I can place files. It's possible to use both multiple form inputs (you want these when uploading many files from a directory) and numerous inputs that share a name  (Flexible way to upload an unspecified number of files from different location). It's also possible to append the form with more inputs using JavaScript.
<form action="/files" method="post" enctype="multipart/form-data">
   <fieldset>
       <legend>Multiple inputs with the same name</legend>
       <input type="file" name="test" multiple="multiple"/>
       <input type="file" name="test" />
       <input type="file" name="test" />
   </fieldset>
   <input type="submit" value="Upload It" />
</form>
Service - using FormDataMultipart
Here's a simplified method that reads a collection of files from a multipart form. All inputs with the same are assigned to a List and their values are converted to InputStream using the getValueAs method of FormDataBodyPart. Once you have these files as InputStream instances, it's easy to do almost anything with them. 
@POST
@Path("files")
@Consumes(MediaType.MULTIPART_FORM_DATA)
public Response uploadMultipart(FormDataMultiPart multiPart) throws IOException{
    List<FormDataBodyPart> fields = multiPart.getFields("test");
    for(FormDataBodyPart field : fields){
        handleInputStream(field.getValueAs(InputStream.class));
    }
    //prepare the response
}

private void handleInputStream(InputStream is){
    //read the stream any way you want
}
                        
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