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How do I read / convert an InputStream into a String in Java?


Question

If you have a java.io.InputStream object, how should you process that object and produce a String?


Suppose I have an InputStream that contains text data, and I want to convert it to a String, so for example I can write that to a log file.

What is the easiest way to take the InputStream and convert it to a String?

public String convertStreamToString(InputStream is) {
    // ???
}
2019/01/05
1
4138
1/5/2019 10:28:26 AM

Accepted Answer

A nice way to do this is using Apache commons IOUtils to copy the InputStream into a StringWriter... something like

StringWriter writer = new StringWriter();
IOUtils.copy(inputStream, writer, encoding);
String theString = writer.toString();

or even

// NB: does not close inputStream, you'll have to use try-with-resources for that
String theString = IOUtils.toString(inputStream, encoding); 

Alternatively, you could use ByteArrayOutputStream if you don't want to mix your Streams and Writers

2018/05/21
2573
5/21/2018 1:09:50 PM


Here's a way using only the standard Java library (note that the stream is not closed, your mileage may vary).

static String convertStreamToString(java.io.InputStream is) {
    java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
    return s.hasNext() ? s.next() : "";
}

I learned this trick from "Stupid Scanner tricks" article. The reason it works is because Scanner iterates over tokens in the stream, and in this case we separate tokens using "beginning of the input boundary" (\A), thus giving us only one token for the entire contents of the stream.

Note, if you need to be specific about the input stream's encoding, you can provide the second argument to Scanner constructor that indicates what character set to use (e.g. "UTF-8").

Hat tip goes also to Jacob, who once pointed me to the said article.

2019/01/05

Apache Commons allows:

String myString = IOUtils.toString(myInputStream, "UTF-8");

Of course, you could choose other character encodings besides UTF-8.

Also see: (documentation)

2019/01/05

Taking into account file one should first get a java.io.Reader instance. This can then be read and added to a StringBuilder (we don't need StringBuffer if we are not accessing it in multiple threads, and StringBuilder is faster). The trick here is that we work in blocks, and as such don't need other buffering streams. The block size is parameterized for run-time performance optimization.

public static String slurp(final InputStream is, final int bufferSize) {
    final char[] buffer = new char[bufferSize];
    final StringBuilder out = new StringBuilder();
    try (Reader in = new InputStreamReader(is, "UTF-8")) {
        for (;;) {
            int rsz = in.read(buffer, 0, buffer.length);
            if (rsz < 0)
                break;
            out.append(buffer, 0, rsz);
        }
    }
    catch (UnsupportedEncodingException ex) {
        /* ... */
    }
    catch (IOException ex) {
        /* ... */
    }
    return out.toString();
}
2015/07/15

Use:

InputStream in = /* Your InputStream */;
StringBuilder sb = new StringBuilder();
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String read;

while ((read=br.readLine()) != null) {
    //System.out.println(read);
    sb.append(read);
}

br.close();
return sb.toString();
2019/01/05

If you are using Google-Collections/Guava you could do the following:

InputStream stream = ...
String content = CharStreams.toString(new InputStreamReader(stream, Charsets.UTF_8));
Closeables.closeQuietly(stream);

Note that the second parameter (i.e. Charsets.UTF_8) for the InputStreamReader isn't necessary, but it is generally a good idea to specify the encoding if you know it (which you should!)

2013/01/30

Source: https://stackoverflow.com/questions/309424
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