如何将图片作为多部分POST请求的一部分发送 - Java HtmlUnit

Question

I am trying to use Java to submit a captcha to decaptcher.com. Decaptcher doesn't really do a good job of explaining how to use their API's, so I am trying to figure out how to use an HTTP POST request to submit a captcha. Here is the example code I got from their website:

<form 
 method="post" 
 action="http://poster.decaptcher.com/" 
 enctype="multipart/form-data">
 <input type="hidden" name="function"  value="picture2">
 <input type="text"   name="username"  value="client">
 <input type="text"   name="password"  value="qwerty">
 <input type="file"   name="pict">
 <input type="text"   name="pict_to"   value="0">
 <input type="text"   name="pict_type" value="0">
 <input type="submit" value="Send">
</form>

I am supposed to send a post request like that to the web server and get a string returned to me. Here is my attempt to implement that in Java.

public String getDecaptcherAnswer(String username, String password){
        try{
            URL decaptcherPostURL = new URL("http://poster.decaptcher.com/");
            WebRequestSettings request = new WebRequestSettings(decaptcherPostURL, HttpMethod.POST);
            request.setEncodingType(FormEncodingType.MULTIPART);
            ArrayList<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new NameValuePair("function", "picture2"));
            params.add(new NameValuePair("username", username));
            params.add(new NameValuePair("password", password));

            //I added this block in 
            File file = new File("captcha.png");
            params.add(new KeyDataPair("pict", capFile, "png", "utf-8"));
            //----------------------

            params.add(new NameValuePair("pict_to", "0"));
            params.add(new NameValuePair("pict_type", "0"));
            request.setRequestParameters(params);
            request.setUrl(decaptcherPostURL);

            HtmlPage page = webClient.getPage(request);
            System.out.println(page.asText());
            System.out.println("--------------------------------------");
            System.out.println(page.asXml());

            return page.asText();
        }catch (Exception e){
            e.printStackTrace();
            return null;
        }
}

Am I supposed to set the value of pict to a File object instead of the String pointing to where the captcha is stored? (captcha.png is the name of the image I am trying to submit).

Answer 1

There is a higher-level mechanism to send that file, you don't need to create WebRequestSettings and set its individual values.

You should host that static html somewhere and do something like the below.

If you still have an issue, please submit a bug report in HtmlUnit bug tracker.

BTW, HtmlUnit 2.8 is about to be released, give it a try.

WebClient webClient = new WebClient();
HtmlPage page = webClient.getPage("http://some_host/test.html");
HtmlForm form = page.getForms().get(0);
form.getInputByName("username").setValueAttribute(username);
form.getInputByName("password").setValueAttribute(password);
form.getInputByName("pict_to").setValueAttribute("0");
form.getInputByName("pict_type").setValueAttribute("0");
form.getInputByName("pict").setValueAttribute("full_path_to_captcha_png");
form.<HtmlFileInput>getInputByName("pict").setContentType("image/png");//optional
HtmlPage page2 = form.getInputByValue("Send").click();

Answer 2

You should not use a NameValuePair for this but its subclass, KeyDataPair . This way you can specify a file to upload.

The following should work:

new KeyDataPair("pict", new File(fileName), "image/png", "utf-8");

The content type parameter is the MIME type of the file. Since you are uploading a PNG file, it should be image/png .

Answer 3

Here's what I was trying to type:

File file = new File("captcha.png");
params.add(new KeyDataPair("pict", capFile, "png", "utf-8"));

Are PNG files encoded with UTF-8? Is that how I would specify the KeyDataPair for the file input? I think I am either specifying the wrong contentType or the wrong charSet, or both. Am I supposed to put them in all caps?