How to use HttpServletRequest#getParts() in a servlet filter running on Tomcat?

Question

I would like to upload a file in my JSF application. I am using a Filter and HttpServletRequestWrapper to access the upload file.

 public MultipartRequestWrapper(HttpServletRequest request) {
    super(request);
    System.out.println("Created multipart wrapper....");
    try {
        System.out.println("Looping parts"+getParts().size());

        for (Part p : getParts()) {
            System.out.println(String.format("Part name: %1$s, contentType : %2$s", p.getName(), p.getContentType()));
            for(String header : p.getHeaderNames()){
                System.out.println("Header name : " + header + ", value : " + p.getHeader(header));
            }
            byte[] b = new byte[(int) p.getSize()];
            p.getInputStream().read(b);
            params.put(p.getName(), new String[]{new String(b)});
        }
    } catch (IOException ex) {
        ex.printStackTrace();
        Logger.getLogger(MultipartRequestWrapper.class.getName()).log(Level.SEVERE, null, ex);
    } catch (ServletException ex) {
         ex.printStackTrace();
        Logger.getLogger(MultipartRequestWrapper.class.getName()).log(Level.SEVERE, null, ex);
    }

However, getParts() returns an empty collection. How can I enable multipart/form-data parsing in a servlet filter in Tomcat 7.0.8?

Answer 1

In order to get HttpServletRequest#getParts() to work in a Filter in Tomcat, you need to set allowCasualMultipartParsing="true" in the webapp's <Context> element in Webapp/META-INF/context.xml or Tomcat/conf/server.xml.

<Context ... allowCasualMultipartParsing="true">

Because as per the servlet 3.0 specification the HttpServletRequest#getParts() should only be available inside a HttpServlet with the @MultipartConfig annotation. See also the documentation of the <Context> element:

allowCasualMultipartParsing

Set to true if Tomcat should automatically parse multipart/form-data request bodies when HttpServletRequest.getPart* or HttpServletRequest.getParameter* is called, even when the target servlet isn't marked with the @MultipartConfig annotation (See Servlet Specification 3.0, Section 3.2 for details). Note that any setting other than false causes Tomcat to behave in a way that is not technically spec-compliant. The default is false.

See also:

• Tomcat 7 issue 49711
• Uploading files in Servlet 3.0
• Uploading files in JSF 2.0 and Servlet 3.0

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Unrelated to the concrete problem, the following is definitely not right:

byte[] b = new byte[(int) p.getSize()];
p.getInputStream().read(b);
params.put(p.getName(), new String[]{new String(b)});

First, you are not respecting the character encoding specified by the client -if any. Second, this will fail for binary files.