How to Mock a javax.servlet.ServletInputStream

Question

I am creating some unit testing and trying to Mock out some calls. Here is what I have in my working code:

String soapRequest = (SimUtil.readInputStream(request.getInputStream())).toString();
if (soapRequest.equals("My String")) { ... }

and SimUtil.readInputSteam looks like this:

StringBuffer sb = new StringBuffer();
BufferedReader reader = null;
try  {
    reader = new BufferedReader(new InputStreamReader(inputStream));
    final int buffSize = 1024;
    char[] buf = new char[buffSize];
    int numRead = 0;
    while ((numRead = reader.read(buf)) != -1) {
        String readData = String.valueOf(buf, 0, numRead);
        sb.append(readData);
        buf = new char[buffSize];
    }
} catch (IOException e) {
    LOG.error(e.getMessage(), e);
} finally {
    try {
        if (reader != null) {
            reader.close();
        }
    } catch (IOException e) {
        LOG.error(e.getMessage(), e);
    }
}

What I am trying to do is the request.getInputStream(), the stream returns certain String.

HttpServletRequest request = mock(HttpServletRequest.class);
ServletInputStream inputStream = mock(ServletInputStream.class);
when(request.getInputStream()).thenReturn(inputStream);

So This is the code I want to condition

when(inputStream.read()).thenReturn("My String".toInt());

Any Help would be greatly appreciated.

Answer 1

Don't mock the InputStream. Instead, transform the String to an array of bytes using the getBytes() method. Then create a ByteArrayInputStream with the array as input, so that it returns the String when consumed, each byte at a time. Next, create a ServletInputStream that wraps a regular InputStream like the one from Spring:

public class DelegatingServletInputStream extends ServletInputStream {

    private final InputStream sourceStream;


    /**
     * Create a DelegatingServletInputStream for the given source stream.
     * @param sourceStream the source stream (never <code>null</code>)
     */
    public DelegatingServletInputStream(InputStream sourceStream) {
        Assert.notNull(sourceStream, "Source InputStream must not be null");
        this.sourceStream = sourceStream;
    }

    /**
     * Return the underlying source stream (never <code>null</code>).
     */
    public final InputStream getSourceStream() {
        return this.sourceStream;
    }


    public int read() throws IOException {
        return this.sourceStream.read();
    }

    public void close() throws IOException {
        super.close();
        this.sourceStream.close();
    }

}

and finally, the HttpServletRequest mock would return this DelegatingServletInputStream object.