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Log response body in case of exception

I am using retrofit for http calls with gson as a converter.
In some cases I get exceptions thrown when gson tries to convert response to object and I would like to know what is the actual response in such case.
For example:
This is the exception message I get:
Expected a string but was BEGIN_OBJECT at line 1 column 26 path $[0].date
The code that execute the call is like this:
Gson gson = gsonBuilder.create();
Retrofit retrofit = (new retrofit2.Retrofit.Builder()).baseUrl(baseUrl).addConverterFactory(GsonConverterFactory.create(gson)).client(httpClient).build();
MyService service = retrofit.create(clazz);
...
Response<T> response = service.call().execute();
When this code throws exception I would like to log the raw response body somehow. How can I do that?

I don't think it can be accomplished easily. Retrofit does not seem to provide an easy way of tracking input streams (the most natural place I was thinking of was CallAdapter.Factory but it does not allow invalid response tracking).
Basically, illegal response conversion should be detected in a particular converter whose only responsibility is logging invalid payloads. Sounds pretty much like the Decorator design pattern. Since Java (unlike Kotlin?) does not support decorators as a first-class citizen, forwarding implementations can be implemented similarly to Google Guava Forwarding*** classes:
ForwardingInputStream.java
#SuppressWarnings("resource")
abstract class ForwardingInputStream
extends InputStream {
protected abstract InputStream inputStream();
// #formatter:off
#Override public int read() throws IOException { return inputStream().read(); }
// #formatter:on
// #formatter:off
#Override public int read(final byte[] b) throws IOException { return inputStream().read(b); }
#Override public int read(final byte[] b, final int off, final int len) throws IOException { return inputStream().read(b, off, len); }
#Override public long skip(final long n) throws IOException { return inputStream().skip(n); }
#Override public int available() throws IOException { return inputStream().available(); }
#Override public void close() throws IOException { inputStream().close(); }
#Override public void mark(final int readlimit) { inputStream().mark(readlimit); }
#Override public void reset() throws IOException { inputStream().reset(); }
#Override public boolean markSupported() { return inputStream().markSupported(); }
// #formatter:on
}
ForwardingResponseBody.java
#SuppressWarnings("resource")
abstract class ForwardingResponseBody
extends ResponseBody {
protected abstract ResponseBody responseBody();
// #formatter:off
#Override public MediaType contentType() { return responseBody().contentType(); }
#Override public long contentLength() { return responseBody().contentLength(); }
#Override public BufferedSource source() { return responseBody().source(); }
// #formatter:on
// #formatter:off
#Override public void close() { super.close(); }
// #formatter:on
}
ForwardingBufferedSource.java
abstract class ForwardingBufferedSource
implements BufferedSource {
protected abstract BufferedSource bufferedSource();
// #formatter:off
#Override public Buffer buffer() { return bufferedSource().buffer(); }
#Override public boolean exhausted() throws IOException { return bufferedSource().exhausted(); }
#Override public void require(final long byteCount) throws IOException { bufferedSource().require(byteCount); }
#Override public boolean request(final long byteCount) throws IOException { return bufferedSource().request(byteCount); }
#Override public byte readByte() throws IOException { return bufferedSource().readByte(); }
#Override public short readShort() throws IOException { return bufferedSource().readShort(); }
#Override public short readShortLe() throws IOException { return bufferedSource().readShortLe(); }
#Override public int readInt() throws IOException { return bufferedSource().readInt(); }
#Override public int readIntLe() throws IOException { return bufferedSource().readIntLe(); }
#Override public long readLong() throws IOException { return bufferedSource().readLong(); }
#Override public long readLongLe() throws IOException { return bufferedSource().readLongLe(); }
#Override public long readDecimalLong() throws IOException { return bufferedSource().readDecimalLong(); }
#Override public long readHexadecimalUnsignedLong() throws IOException { return bufferedSource().readHexadecimalUnsignedLong(); }
#Override public void skip(final long byteCount) throws IOException { bufferedSource().skip(byteCount); }
#Override public ByteString readByteString() throws IOException { return bufferedSource().readByteString(); }
#Override public ByteString readByteString(final long byteCount) throws IOException { return bufferedSource().readByteString(byteCount); }
#Override public int select(final Options options) throws IOException { return bufferedSource().select(options); }
#Override public byte[] readByteArray() throws IOException { return bufferedSource().readByteArray(); }
#Override public byte[] readByteArray(final long byteCount) throws IOException { return bufferedSource().readByteArray(byteCount); }
#Override public int read(final byte[] sink) throws IOException { return bufferedSource().read(sink); }
#Override public void readFully(final byte[] sink) throws IOException { bufferedSource().readFully(sink); }
#Override public int read(final byte[] sink, final int offset, final int byteCount) throws IOException { return bufferedSource().read(sink, offset, byteCount); }
#Override public void readFully(final Buffer sink, final long byteCount) throws IOException { bufferedSource().readFully(sink, byteCount); }
#Override public long readAll(final Sink sink) throws IOException { return bufferedSource().readAll(sink); }
#Override public String readUtf8() throws IOException { return bufferedSource().readUtf8(); }
#Override public String readUtf8(final long byteCount) throws IOException { return bufferedSource().readUtf8(byteCount); }
#Override public String readUtf8Line() throws IOException { return bufferedSource().readUtf8Line(); }
#Override public String readUtf8LineStrict() throws IOException { return bufferedSource().readUtf8LineStrict(); }
#Override public int readUtf8CodePoint() throws IOException { return bufferedSource().readUtf8CodePoint(); }
#Override public String readString(final Charset charset) throws IOException { return bufferedSource().readString(charset); }
#Override public String readString(final long byteCount, final Charset charset) throws IOException { return bufferedSource().readString(byteCount, charset); }
#Override public long indexOf(final byte b) throws IOException { return bufferedSource().indexOf(b); }
#Override public long indexOf(final byte b, final long fromIndex) throws IOException { return bufferedSource().indexOf(b, fromIndex); }
#Override public long indexOf(final ByteString bytes) throws IOException { return bufferedSource().indexOf(bytes); }
#Override public long indexOf(final ByteString bytes, final long fromIndex) throws IOException { return bufferedSource().indexOf(bytes, fromIndex); }
#Override public long indexOfElement(final ByteString targetBytes) throws IOException { return bufferedSource().indexOfElement(targetBytes); }
#Override public long indexOfElement(final ByteString targetBytes, final long fromIndex) throws IOException { return bufferedSource().indexOfElement(targetBytes, fromIndex); }
#Override public InputStream inputStream() { return bufferedSource().inputStream(); }
#Override public long read(final Buffer sink, final long byteCount) throws IOException { return bufferedSource().read(sink, byteCount); }
#Override public Timeout timeout() { return bufferedSource().timeout(); }
#Override public void close() throws IOException { bufferedSource().close(); }
// #formatter:on
}
Trivial forwarding implementations just override all methods of their parent classes and delegate the job to a delegated object. Once a forwarding class is extended, some of the parent methods can be overridden again.
IConversionThrowableConsumer.java
This is just a listener used below.
interface IConversionThrowableConsumer {
/**
* Instantiating {#link okhttp3.ResponseBody} can be not easy due to the way of how {#link okio.BufferedSource} is designed -- too heavy.
* Deconstructing its components to "atoms" with some lack of functionality may be acceptable.
* However, this consumer may need some improvements on demand.
*/
void accept(MediaType contentType, long contentLength, InputStream inputStream, Throwable ex)
throws IOException;
}
ErrorReportingConverterFactory.java
The next step is implementating the error-reporting converter factory that can be injected to Retrofit.Builder and listen to any errors occurring in downstream converters. Note how it works:
For every response converter an intermediate converter is injected. It allows to listen to any error in downstream converters.
Downstream converters obtain a non-closeable resources in order not to close underlaying I/O resources prematurely...
Downstream converters convert whilst the intermediate converter collects the real input stream content into a buffer in order to respond with an input stream that may cause GsonConverter fail. This should be considered a bottleneck here due to possibly large size of the grown buffer (however, it may be limited), its internal array is copied when requested from the converter and so on.
If IOException or RuntimeException occur, the intermediate converter concatenates the buffered input stream content and the real input stream in order to let a consumer to accept input streams from the very beginning.
The intermediate converter takes care of closing resources itself.
final class ErrorReportingConverterFactory
extends Factory {
private final IConversionThrowableConsumer consumer;
private ErrorReportingConverterFactory(final IConversionThrowableConsumer consumer) {
this.consumer = consumer;
}
static Factory getErrorReportingConverterFactory(final IConversionThrowableConsumer listener) {
return new ErrorReportingConverterFactory(listener);
}
#Override
public Converter<ResponseBody, ?> responseBodyConverter(final Type type, final Annotation[] annotations, final Retrofit retrofit) {
return (Converter<ResponseBody, Object>) responseBody -> {
final ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
final InputStream realInputStream = responseBody.byteStream();
try {
final ForwardingResponseBody bufferingResponseBody = new BufferingNoCloseResponseBOdy(responseBody, byteArrayOutputStream);
final Converter<ResponseBody, Object> converter = retrofit.nextResponseBodyConverter(this, type, annotations);
return converter.convert(bufferingResponseBody);
} catch ( final RuntimeException | IOException ex ) {
final InputStream inputStream = concatInputStreams(new ByteArrayInputStream(byteArrayOutputStream.toByteArray()), realInputStream);
consumer.accept(responseBody.contentType(), responseBody.contentLength(), inputStream, ex);
throw ex;
} finally {
responseBody.close();
}
};
}
private static class BufferingInputStream
extends ForwardingInputStream {
private final InputStream inputStream;
private final ByteArrayOutputStream byteArrayOutputStream;
private BufferingInputStream(final InputStream inputStream, final ByteArrayOutputStream byteArrayOutputStream) {
this.inputStream = inputStream;
this.byteArrayOutputStream = byteArrayOutputStream;
}
#Override
protected InputStream inputStream() {
return inputStream;
}
#Override
public int read()
throws IOException {
final int read = super.read();
if ( read != -1 ) {
byteArrayOutputStream.write(read);
}
return read;
}
#Override
public int read(final byte[] b)
throws IOException {
final int read = super.read(b);
if ( read != -1 ) {
byteArrayOutputStream.write(b, 0, read);
}
return read;
}
#Override
public int read(final byte[] b, final int off, final int len)
throws IOException {
final int read = super.read(b, off, len);
if ( read != -1 ) {
byteArrayOutputStream.write(b, off, read);
}
return read;
}
}
private static class BufferingNoCloseResponseBOdy
extends ForwardingResponseBody {
private final ResponseBody responseBody;
private final ByteArrayOutputStream byteArrayOutputStream;
private BufferingNoCloseResponseBOdy(final ResponseBody responseBody, final ByteArrayOutputStream byteArrayOutputStream) {
this.responseBody = responseBody;
this.byteArrayOutputStream = byteArrayOutputStream;
}
#Override
protected ResponseBody responseBody() {
return responseBody;
}
#Override
#SuppressWarnings("resource")
public BufferedSource source() {
final BufferedSource source = super.source();
return new ForwardingBufferedSource() {
#Override
protected BufferedSource bufferedSource() {
return source;
}
#Override
public InputStream inputStream() {
return new BufferingInputStream(super.inputStream(), byteArrayOutputStream);
}
};
}
/**
* Suppressing close due to automatic close in {#link ErrorReportingConverterFactory#responseBodyConverter(Type, Annotation[], Retrofit)}
*/
#Override
public void close() {
// do nothing
}
}
}
Note that this implementation uses forwarding classes heavily and only overrides what's necessary.
Also there are some utilities like concatenating input streams and adapting iterators to enumerations.
IteratorEnumeration.java
final class IteratorEnumeration<T>
implements Enumeration<T> {
private final Iterator<? extends T> iterator;
private IteratorEnumeration(final Iterator<? extends T> iterator) {
this.iterator = iterator;
}
static <T> Enumeration<T> iteratorEnumeration(final Iterator<? extends T> iterator) {
return new IteratorEnumeration<>(iterator);
}
#Override
public boolean hasMoreElements() {
return iterator.hasNext();
}
#Override
public T nextElement() {
return iterator.next();
}
}
InputStreams.java
final class InputStreams {
private InputStreams() {
}
static InputStream concatInputStreams(final InputStream... inputStreams) {
return inputStreams.length == 2
? new SequenceInputStream(inputStreams[0], inputStreams[1])
: new SequenceInputStream(iteratorEnumeration((Iterator<? extends InputStream>) asList(inputStreams).iterator()));
}
}
OutputStreamConversionThrowableConsumer.java
Trivial logging implementation.
final class OutputStreamConversionThrowableConsumer
implements IConversionThrowableConsumer {
private static final int BUFFER_SIZE = 512;
private final PrintStream printStream;
private OutputStreamConversionThrowableConsumer(final PrintStream printStream) {
this.printStream = printStream;
}
static IConversionThrowableConsumer getOutputStreamConversionThrowableConsumer(final OutputStream outputStream) {
return new OutputStreamConversionThrowableConsumer(new PrintStream(outputStream));
}
static IConversionThrowableConsumer getSystemOutConversionThrowableConsumer() {
return getOutputStreamConversionThrowableConsumer(System.out);
}
static IConversionThrowableConsumer getSystemErrConversionThrowableConsumer() {
return getOutputStreamConversionThrowableConsumer(System.err);
}
#Override
public void accept(final MediaType contentType, final long contentLength, final InputStream inputStream, final Throwable ex)
throws IOException {
printStream.print("Content type: ");
printStream.println(contentType);
printStream.print("Content length: ");
printStream.println(contentLength);
printStream.print("Content: ");
final byte[] buffer = new byte[BUFFER_SIZE];
int read;
while ( (read = inputStream.read(buffer)) != -1 ) {
printStream.write(buffer, 0, read);
}
printStream.println();
}
}
Put all together
final Gson gson = new Gson();
final Retrofit retrofit = new Retrofit.Builder()
.baseUrl(...)
.addConverterFactory(getErrorReportingConverterFactory(getSystemOutConversionThrowableConsumer()))
.addConverterFactory(GsonConverterFactory.create(gson))
.build();
final IWhateverService service = retrofit.create(IWhateverService.class);
final Call<...> call = service.getWhatever("test.json");
call.enqueue(new Callback<...>() {
#Override
public void onResponse(final Call<...> call, final Response<...> response) {
System.out.println(response.body());
}
#Override
public void onFailure(final Call<...> call, final Throwable throwable) {
throwable.printStackTrace(System.err);
}
});
Note that ErrorReportingConverterFactory must registered before the GsonConverterFactory. Let's assume the service requests for a JSON that's eventually illegal:
{"foo":1,###"bar":2}
In such case, the error reporting converter will produce the following dump to stdout:
Content type: application/json
Content length: -1
Content: {"foo":1,###"bar":2}
I'm not an expert in Log4j, and could not find an efficient way to get the output streams to redirect the input stream to. Here is the closest thing what I've found:
final class Log4jConversionThrowableConsumer
implements IConversionThrowableConsumer {
private static final int BUFFER_SIZE = 512;
private final Logger logger;
private Log4jConversionThrowableConsumer(final Logger logger) {
this.logger = logger;
}
static IConversionThrowableConsumer getLog4jConversionThrowableConsumer(final Logger logger) {
return new Log4jConversionThrowableConsumer(logger);
}
#Override
public void accept(final MediaType contentType, final long contentLength, final InputStream inputStream, final Throwable ex) {
try {
final StringBuilder builder = new StringBuilder(BUFFER_SIZE)
.append("Content type=")
.append(contentType)
.append("; Content length=")
.append(contentLength)
.append("; Input stream content=");
readInputStreamFirstChunk(builder, inputStream);
logger.error(builder.toString(), ex);
} catch ( final IOException ioex ) {
throw new RuntimeException(ioex);
}
}
private static void readInputStreamFirstChunk(final StringBuilder builder, final InputStream inputStream)
throws IOException {
final Reader reader = new InputStreamReader(inputStream);
final char[] buffer = new char[512];
final int read = reader.read(buffer);
if ( read >= 0 ) {
builder.append(buffer, 0, read);
}
}
}
Unfortunately, collecting the whole string may be expensive, so it only takes the very first 512 bytes. This may require callibrating the joined streams in the intermediate converter in order to "shift" the content "to the left" a bit.

Parquet Writer to buffer or byte stream

I have a java application that converts json messages to parquet format. Is there any parquet writer which writes to buffer or byte stream in java? Most of the examples, I have seen write to files.

TLDR; you will need to implement OutputFile, e.g. something along the line of:
import org.apache.parquet.io.OutputFile;
import org.apache.parquet.io.PositionOutputStream;
import java.io.BufferedOutputStream;
import java.io.IOException;
public class ParquetBufferedWriter implements OutputFile {
private final BufferedOutputStream out;
public ParquetBufferedWriter(BufferedOutputStream out) {
this.out = out;
}
#Override
public PositionOutputStream create(long blockSizeHint) throws IOException {
return createPositionOutputstream();
}
private PositionOutputStream createPositionOutputstream() {
return new PositionOutputStream() {
#Override
public long getPos() throws IOException {
return 0;
}
#Override
public void write(int b) throws IOException {
out.write(b);
}
};
}
#Override
public PositionOutputStream createOrOverwrite(long blockSizeHint) throws IOException {
return createPositionOutputstream();
}
#Override
public boolean supportsBlockSize() {
return false;
}
#Override
public long defaultBlockSize() {
return 0;
}
}
And your writer would be something like:
ParquetBufferedWriter out = new ParquetBufferedWriter();
try (ParquetWriter<Record> writer = AvroParquetWriter.
<Record>builder(out)
.withRowGroupSize(DEFAULT_BLOCK_SIZE)
.withPageSize(DEFAULT_PAGE_SIZE)
.withSchema(SCHEMA)
.build()) {
for (Record record : records) {
writer.write(record);
}
} catch (IOException e) {
throw new IllegalStateException(e);
}

I just also needed to write to a stream, so I completed the example given by naimdjon. The following works perfectly fine for me.
class ParquetBufferedWriter implements OutputFile {
private final BufferedOutputStream out;
public ParquetBufferedWriter(BufferedOutputStream out) {
this.out = out;
}
#Override
public PositionOutputStream create(long blockSizeHint) throws IOException {
return createPositionOutputstream();
}
private PositionOutputStream createPositionOutputstream() {
return new PositionOutputStream() {
int pos = 0;
#Override
public long getPos() throws IOException {
return pos;
}
#Override
public void flush() throws IOException {
out.flush();
};
#Override
public void close() throws IOException {
out.close();
};
#Override
public void write(int b) throws IOException {
out.write(b);
pos++;
}
#Override
public void write(byte[] b, int off, int len) throws IOException {
out.write(b, off, len);
pos += len;
}
};
}
#Override
public PositionOutputStream createOrOverwrite(long blockSizeHint) throws IOException {
return createPositionOutputstream();
}
#Override
public boolean supportsBlockSize() {
return false;
}
#Override
public long defaultBlockSize() {
return 0;
}
}

You need to write the data into temp file and then covert the data from file to input stream or buffer
something like this, first read the tempfile data
final InputStream targetStream = new DataInputStream(new FileInputStream(tmp1.getAbsoluteFile()));
StringWriter writer = new StringWriter();
String encoding = StandardCharsets.UTF_8.name();
IOUtils.copy(targetStream, writer, encoding);
System.out.println(writer);

load html on Blackberry4.6 os version

Hi I'm new in Blackberry app development i want to load HTML in browser field..
I'm able to load HTML for version 5 ,and 6 and more but it not loading in OS version 4
plz tell me how to load this HTML on Blackberry OS version4.6 i m using Eclipsed
to developing application on 5 and 6 works properly but in 4.6 not plz tell me how to write. Code for this or any specific change in code or we cant load HTML in OS version 4.6?
BrowserField mybroBrowserField=new BrowserField();
add(mybroBrowserField);
mybroBrowserField.displayContent(
"<html><body><h1>hello world! This blackbery apps</h1> </body></html>",
"http://localhost");
this code apply for 5 and more than 5 version but not work for OS version 4

You can show your html document in this way
BrowserSession session = Browser.getDefaultSession();
session.displayPage("cod://Name of your application code file/test.html");

If you are using BlackBerry Eclipse Plug-in to develop BB apps, you can import sample BlackBerry projects. In the list there is something like BlackBerry Browser Field Demo. Just import that and find out how this works. Insert this snippet to Utilities class
private static DataInputStream dataInput;
private static InputStream in;
static HttpConnection makeDummyConnection(String htmlData){
try {
in = new ByteArrayInputStream(htmlData.getBytes("UTF-8"));
dataInput = new DataInputStream(in);
} catch (Exception e) {
System.out.println("HttpConnectionImpl : Exception : " + e);
}
return new HttpConnection() {
public String getURL() {
return "";
}
public String getProtocol() {
return "";
}
public String getHost() {
return "";
}
public String getFile() {
return "";
}
public String getRef() {
return "";
}
public String getQuery() {
return "";
}
public int getPort() {
return 0;
}
public String getRequestMethod() {
return "";
}
public void setRequestMethod(String s) throws IOException {
}
public String getRequestProperty(String s) {
return "";
}
public void setRequestProperty(String s, String s1) throws IOException {
}
public int getResponseCode() throws IOException {
return 200;
}
public String getResponseMessage() throws IOException {
return "";
}
public long getExpiration() throws IOException {
return 0;
}
public long getDate() throws IOException {
return 0;
}
public long getLastModified() throws IOException {
return 0;
}
public String getHeaderField(String s) throws IOException {
return "";
}
public int getHeaderFieldInt(String s, int i) throws IOException {
return 0;
}
public long getHeaderFieldDate(String s, long l) throws IOException {
return 0;
}
public String getHeaderField(int i) throws IOException {
return "";
}
public String getHeaderFieldKey(int i) throws IOException {
return "";
}
public String getType() {
return "text/html";
}
public String getEncoding() {
return "text/html";
}
public long getLength() {
return 7000;
}
public InputStream openInputStream() throws IOException {
return in;
}
public DataInputStream openDataInputStream() throws IOException {
return dataInput;
}
public void close() throws IOException {
}
public OutputStream openOutputStream() throws IOException {
return new ByteArrayOutputStream();
}
public DataOutputStream openDataOutputStream() throws IOException {
return new DataOutputStream(new ByteArrayOutputStream());
}
};
}
and call this instead of makeConnection(String url, HttpHeaders requestHeaders, byte[] postData) method.

BrowserField exist only since BlackBerry API 5.0.0, but you can use this custom BrowserFieldRenderer class from LogicMail to solve your problem

Is there a SignatureOutputStream (or equivalent) in Java?

I note that there is a CipherOutputStream in Java, but apparently no SignatureOutputStream. Is this true? Where might I find a SignatureOutputStream?

Here is an example implementation, just for you. It comes with a test function (see below).
package de.fencing_game.paul.examples;
import java.io.*;
import java.security.*;
/**
* This class provides an outputstream which writes everything
* to a Signature as well as to an underlying stream.
*/
public class SignatureOutputStream
extends OutputStream
{
private OutputStream target;
private Signature sig;
/**
* creates a new SignatureOutputStream which writes to
* a target OutputStream and updates the Signature object.
*/
public SignatureOutputStream(OutputStream target, Signature sig) {
this.target = target;
this.sig = sig;
}
public void write(int b)
throws IOException
{
write(new byte[]{(byte)b});
}
public void write(byte[] b)
throws IOException
{
write(b, 0, b.length);
}
public void write(byte[] b, int offset, int len)
throws IOException
{
target.write(b, offset, len);
try {
sig.update(b, offset, len);
}
catch(SignatureException ex) {
throw new IOException(ex);
}
}
public void flush()
throws IOException
{
target.flush();
}
public void close()
throws IOException
{
target.close();
}
}
Here are some test methods to show how to use this:
private static byte[] signData(OutputStream target,
PrivateKey key, String[] data)
throws IOException, GeneralSecurityException
{
Signature sig = Signature.getInstance("SHA1withRSA");
sig.initSign(key);
DataOutputStream dOut =
new DataOutputStream(new SignatureOutputStream(target, sig));
for(String s : data) {
dOut.writeUTF(s);
}
byte[] signature = sig.sign();
return signature;
}
private static void verify(PublicKey key, byte[] signature,
byte[] data)
throws IOException, GeneralSecurityException
{
Signature sig = Signature.getInstance("SHA1withRSA");
sig.initVerify(key);
ByteArrayOutputStream collector =
new ByteArrayOutputStream(data.length);
OutputStream checker = new SignatureOutputStream(collector, sig);
checker.write(data);
if(sig.verify(signature)) {
System.err.println("Signature okay");
}
else {
System.err.println("Signature falsed!");
}
}
/**
* a test method.
*/
public static void main(String[] params)
throws IOException, GeneralSecurityException
{
if(params.length < 1) {
params = new String[] {"Hello", "World!"};
}
KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA");
KeyPair pair = gen.generateKeyPair();
ByteArrayOutputStream arrayStream = new ByteArrayOutputStream();
byte[] signature = signData(arrayStream, pair.getPrivate(), params);
byte[] data = arrayStream.toByteArray();
verify(pair.getPublic(), signature, data);
// change one byte by one
data[3]++;
verify(pair.getPublic(), signature, data);
data = arrayStream.toByteArray();
verify(pair.getPublic(), signature, data);
// change signature
signature[4]++;
verify(pair.getPublic(), signature, data);
}
The main method signs its command line parameters with a new (random) private key, and then checks it with the corresponding public key. It again checks it with a bit changed data and signature.
Of course, for the checking of the signature a SignatureInputStream would be more useful - you can create it precisely the same way.

Java: How to get upload and download speed

I write a program to upload and download files to FTP server but I can not monitor the speed and the transfer rate.
I used FTPClient class and its two methods retrievFile() and storeFile()

Give this a try:
public class ReportingOutputStream extends OutputStream {
public static final String BYTES_PROP = "Bytes";
private FileOutputStream fileStream;
private long byteCount = 0L;
private long lastByteCount = 0L;
private long updateInterval = 1L << 10;
private long nextReport = updateInterval;
private PropertyChangeSupport changer = new PropertyChangeSupport(this);
public ReportingOutputStream(File f) throws IOException {
fileStream = new FileOutputStream(f);
}
public void setUpdateInterval(long bytes) {
updateInterval = bytes;
nextReport = updateInterval;
}
#Override
public void write(int b) throws IOException {
byte[] bytes = { (byte) (b & 0xFF) };
write(bytes, 0, 1);
}
#Override
public void write(byte[] b, int off, int len) throws IOException {
fileStream.write(b, off, len);
byteCount += len;
if (byteCount > nextReport) {
changer.firePropertyChange( BYTES_PROP, lastByteCount, byteCount);
lastByteCount = byteCount;
nextReport += updateInterval;
}
}
#Override
public void close() throws IOException {
if (fileStream != null) {
fileStream.close();
fileStream = null;
}
}
public void removePropertyChangeListener(String propertyName, PropertyChangeListener listener) {
changer.removePropertyChangeListener(propertyName, listener);
}
public void addPropertyChangeListener(String propertyName, PropertyChangeListener listener) {
changer.addPropertyChangeListener(propertyName, listener);
}
}
After creating the stream, add a property change listener for BYTES_PROP. By default it fires the handler for every 1 KB received. Call setUpdateInterval to change.

Since retrieveFile and storeFile deal with input and output streams, is it possible for you to write your own subclasses that can monitor the number of bytes transferred in or out over a certain time?