InputStream丢失

Question

我有一门课名为: ServiceCaller.java

该类包含一个用于调用web服务的方法：

public static Response callService(String strURL, String Token, int timeout, Boolean isPostMethod) {

    String error = "";
    int statusCode = HttpStatus.SC_INTERNAL_SERVER_ERROR;

    HttpURLConnection urlConnection = null;

    try
    {
        URL url = new URL(strURL);

        // Allow non trusted ssl certificates
        if(strURL.startsWith("https"))
        {               
            TrustManagerManipulator.allowAllSSL();
        }

        urlConnection = (HttpURLConnection) url.openConnection();

        if (isPostMethod) {
            urlConnection.setRequestMethod("POST");
        }
        else {
            urlConnection.setRequestMethod("GET");
        }

        // Allow Inputs                                                     
        urlConnection.setDoInput(true);                                              

        // Allow Outputs                                                    
        urlConnection.setDoOutput(true);                                             

        // Don't use a cached copy.                                         
        urlConnection.setUseCaches(false);       

        urlConnection.setRequestProperty("Connection", "Keep-Alive");                

        urlConnection.setRequestProperty("Content-Type", "application/json");     

        urlConnection.setRequestProperty("Token", Helpers.getUTF8Encode(Token));

        urlConnection.setConnectTimeout(timeout);   

        DataOutputStream dos = new DataOutputStream(urlConnection.getOutputStream());
        dos.flush();
        dos.close();

        statusCode = urlConnection.getResponseCode();

        Response r = new Response(statusCode, urlConnection.getInputStream(), "No Exception");

        return r;

    } catch (Exception ex) {

        error = ex.getMessage();

        if (error != null && !error.equals("") && error.contains("401"))
            statusCode = HttpStatus.SC_UNAUTHORIZED;

    } finally {

        urlConnection.disconnect();

    }

    return new Response(statusCode, null, error);

}

下面是响应类：

public static class Response
{
    private int statusCode;
    private InputStream responseStream;
    private String exception;

    public int getStatusCode() {
        return statusCode;
    }

    public InputStream getResponseStream() {
        return responseStream;
    }

    public String getExceptionError() {
        return exception;
    }

    public Response(int code, InputStream stream, String strException)
    {
        this.statusCode = code;
        this.responseStream = stream;
        this.exception = strException;
    }
}

这是我用来测试ServiceCaller中函数的测试类：

    public class TestDemo {

        private static final String EncriptionKey = "keyValueToUse";

        public static void main(String[] args) {

            try {

                String strURL = "http://...";
                String strURL2 = "http://...";
                String Token = "iTcakW5...";
                int timeout = 120000;
                Boolean isPostMethod = true;

                ServiceCaller.Response resp = ServiceCaller.CallService(strURL2, Token, timeout, isPostMethod);

                InputStream inputStream = resp.getResponseStream();
                StringWriter writer = new StringWriter();
                IOUtils.copy(inputStream, writer);
                String resultJSON = writer.toString();

                System.out.println("Status Code: " + resp.getStatusCode());
                System.out.println("JSON String:\n" + resultJSON);
                System.out.println("Exception: " + resp.getExceptionError());

            } catch (Exception e) {

                e.printStackTrace();

            }
        }
    }

下面是执行hte前一段代码的输出：

Status Code: 200
JSON String:

Exception: No Exception

问题是，测试类中返回的InputString似乎是空的，因为对字符串的转换返回一个空字符串，但是如果我在CallService函数中执行相同的代码来转换InputString，则转换是成功的，还请注意，状态代码和异常(字符串)正在正确返回。

Answer 1

public static Response CallService(String strURL, String Token, int timeout, Boolean isPostMethod) {

     HttpURLConnection urlConnection = ...

     ...

     new Response(statusCode, urlConnection.getInputStream(), "No Exception");
}

这个代码丢失在..。可能是最重要的部分。在返回到调用方之前，我猜您正在关闭HttpURLConnection。您如何做到这一点可能会有所不同：

• 您只需在return之前关闭它。
• 尝试-抓住-最后:你要关闭它在最后的块。
• 您使用的是Java7中介绍的try-with-resource结构，HttpURLConnection可能会自动关闭。这是不太可能的，因为HttpURLConnection没有实现AutoClosable。

Answer 2

我首先从InputStream中获取HttpURLConnection，然后将其转换为字节数组，然后将该字节数组放入ByteArrayInputStream中，从而解决了问题

byte[] bytes = IOUtils.toByteArray(urlConnection.getInputStream());
ByteArrayInputStream byteStream = new ByteArrayInputStream(bytes);

return new Response(statusCode, byteStream, "");

根据文档，ByteArrayInputStream：

公共ByteArrayInputStream(byte[] buf)创建一个ByteArrayInputStream，以便使用buf作为其缓冲区数组。缓冲区数组未被复制。pos的初始值为0，计数的初始值为buf的长度。参数: buf -输入缓冲区。

Answer 3

问题在于您已经在使用InputStream方法中的CallService方法。

statusCode = urlConnection.getResponseCode();
Response resp = new Response(statusCode, urlConnection.getInputStream(), "");
InputStream inputStream = resp.getResponseStream();
StringWriter writer = new StringWriter();
IOUtils.copy(inputStream, writer); // consuming the stream
String resultJSON = writer.toString(); // you never use this, so why is it here?

因此，当您尝试在main()中再次读取它时，就没有剩下的字节了。

您只能从其中读取一次字节。

这不会引发任何异常，因为IOUtils只调用InputStream#read(...)，如果到达EOF，则返回-1。

注意，Java命名约定规定方法名称应该以小写字符开头。