Read files with Okio

IoUtils.java

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;

import okhttp3.internal.io.FileSystem;
import okio.BufferedSource;
import okio.Okio;

/**
 * Utils for I/O operations.
 */
public class IoUtils {
    /**
     * Reads file and returns a String.
     *
     * @param file the file to read
     * @return the string with file content or null
     */
    @Nullable
    public static String tryReadFile(@NonNull final File file) {
        final BufferedSource source;
        try {
            source = Okio.buffer(FileSystem.SYSTEM.source(file));
            return source.readUtf8();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }

    /**
     * Reads InputStream and returns a String. It will close stream after usage.
     *
     * @param stream the stream to read
     * @return the string with file content or null
     */
    @Nullable
    public static String tryReadFile(@NonNull final InputStream stream) {
        final BufferedSource source = Okio.buffer(Okio.source(stream));
        try {
            return source.readUtf8();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }

    /**
     * Reads file and returns a String.
     *
     * @param file the file to read
     * @return the string content
     */
    @NonNull
    public static String readFile(@NonNull final File file) throws IOException {
        final BufferedSource source = Okio.buffer(FileSystem.SYSTEM.source(file));
        return source.readUtf8();
    }

    /**
     * Reads InputStream and returns a String. It will close stream after usage.
     *
     * @param stream the stream to read
     * @return the string content
     */
    @NonNull
    public static String readFile(@NonNull final InputStream stream) throws IOException {
        final BufferedSource source = Okio.buffer(Okio.source(stream));
        return source.readUtf8();
    }
}

Edited version of https://gist.github.com/ultraon/c6397dfb23de2f260f81e6946ad5adc2 that supports Android API below 19