I have created an application which reads & writes into a remote file. I have different files (A.properties, B.properties, C.properties) in different directories (folder-1, folder-2, folder-3). Each directory has the same filename with different data.
I have implemented concurrency in my application by using the LockRegistry provided by this other answer. The issue is that if a thread is accessing A.properties while another thread accesses B.properties, the propertyMap displayed to the end user will contain both data from property files. How can I resolve this issue?
My code:
public class UDEManager
{
private Map<String, String> propertyMap = new TreeMap<>();
HttpSession session = null;
public UDEPropertyManager()
{
super();
}
public void init(ServletConfig config) throws ServletException
{
super.init(config);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
// Code for calling thread for read/write operations into remote
// file and fill the propertyMap
}
}
class WebAppProperty implements Runnable
{
private WebApp webapp; // folder-1
private String propertyFile; // A.properties
private String keyValue; //messages-title=Messages
private LockType mode;
public String getPropertyFile()
{
return propertyFile;
}
public void setPropertyFile(String propertyFile)
{
this.propertyFile = propertyFile;
}
#Override
public void run()
{
try {
LockRegistry.INSTANCE.acquire(propertyFile, mode);
if (this.mode == LockType.WRITE) {
writeToPropertyFile();
} else if (this.mode == LockType.READ) {
getProperty(this.webapp, this.propertyFile);
}
} catch (Exception ie) {
sysoutAndLog("Thread is Interrupted");
ie.printStackTrace();
} finally {
LockRegistry.INSTANCE.release(propertyFile, mode);
}
}
private boolean getProperty(WebApp webapp, String property)
{
try {
// read from file and put it into Map instance variable
// of calling class (UDEManager)
propertyMap.put(key, value);
} catch(Exception e) {
sysoutAndLog("Error while reading property ");
e.printStackTrace();
}
return false;
}
private void writeToPropertyFile()
{
try {
// Write data into remote file
} catch (Exception e) {
sysoutAndLog("exception while writing to file.");
e.printStackTrace();
}
}
}
You should associate the properties map with the user session or request
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.
The init method gets called again and again on every request in servlet.
Here is the code:
public class PersonInfoController extends HttpServlet {
private static final long serialVersionUID = 1L;
public PersonInfoController() {
super();
}
public void init() throws ServletException {
Connection connection = Database.getConnection();
System.out.println("init method");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
List<PersonInfoServiceI> myList = new ArrayList();
PersonInfoServiceI instance = new PersonInfoServiceImpl();
myList = instance.getdata();
String jsonstring = new Gson().toJson(myList);
request.setAttribute("List", jsonstring);
RequestDispatcher rd = request.getRequestDispatcher("showdata.jsp");
rd.forward(request, response);
}
public void destroy() {
System.out.println("the destory");
}
}
According to your code init() should call only once when servlet will load on first request. Then after its destruction init() will be called again on new request. In between only your service method will be called. Your code is good having no logical mistakes.
Are you calling init method outside the servlet?
Can you attach you deployment descriptor?
I asked a question regarding HTTP Upgrade handling in Servlet 3.1 on wildfly-dev mailing list how to develop simple bi-directional full-duplex echo protocol. After few days of discussion we concluded that the following example is somewhat correct:
#WebServlet(urlPatterns = "/upgrade")
public class AsyncEchoUpgradeServlet extends HttpServlet {
private static final long serialVersionUID = -6955518532146927509L;
#Override
protected void doGet(final HttpServletRequest req,
final HttpServletResponse resp) throws ServletException, IOException {
req.upgrade(Handler.class);
}
public static class Handler implements HttpUpgradeHandler {
#Override
public void init(final WebConnection wc) {
Listener listener = new Listener(wc);
try {
// we have to set the write listener before the read listener
// otherwise the output stream could be written to before it is
// in async mode
wc.getOutputStream().setWriteListener(listener);
wc.getInputStream().setReadListener(listener);
} catch (IOException e) {
throw new IllegalArgumentException(e);
}
}
#Override
public void destroy() {
}
}
private static class Listener implements WriteListener, ReadListener {
private final WebConnection connection;
private final Queue<String> queue = new ArrayDeque<String>();
private Listener(final WebConnection connection) {
this.connection = connection;
}
#Override
publicvoid onDataAvailable() throws IOException {
byte[] data = new byte[100];
while (connection.getInputStream().isReady()) {
int read;
if ((read = connection.getInputStream().read(data)) != -1) {
queue.add(new String(data, 0, read));
}
onWritePossible();
}
}
#Override
public void onAllDataRead() throws IOException {
}
#Override
public void onWritePossible() throws IOException {
while (!queue.isEmpty() && connection.getOutputStream().isReady()) {
String data = queue.poll();
connection.getOutputStream().write(data.getBytes());
}
}
#Override
public void onError(final Throwable t) {
}
}
}
It actually works and it is the only example exchanged during our discussion that works well and we don't have to create any additional threads to handle both input and output.
What bothers me in this example is that we call explicitly onWritePossible() from within onDataAvailable().
Does anyone have any other example on HTTP Upgrade using Servlet 3.1 API? Is the example shown above correct?
I have RESTful web service which is consumed by javascript. This service returns a content type of "application/json". However, for IE the content type must be "text/html". So I written a filter and wrapper to change the content type when IE is detected as the client. My logic seems to have no effect on the content type. What am I doing wrong?
The filter:
public class IE8Filter implements Filter {
private Logger logger = LoggerHelper.getLogger();
#Override
public void destroy() {}
#Override
public void doFilter(ServletRequest req, ServletResponse res,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
String userAgent = request.getHeader("User-Agent");
logger.debugf("User Agent = '%s'", userAgent);
IE8FilterResponseWrapper wrapper = new IE8FilterResponseWrapper(response);
chain.doFilter(req, wrapper);
if (userAgent.contains("MSIE 8") || userAgent.contains("MSIE 7")) {
wrapper.setContentType("text/html");
logger.debugf("Content Type = '%s'", wrapper.getContentType());
}
}
#Override
public void init(FilterConfig arg0) throws ServletException {}
}
The wrapper:
public class IE8FilterResponseWrapper extends HttpServletResponseWrapper {
private String contentType;
public IE8FilterResponseWrapper(HttpServletResponse response) {
super(response);
}
public void setContentType(String type) {
this.contentType = type;
super.setContentType(type);
}
public String getContentType() {
return contentType;
}
}
I found an answer. The trick was to prevent my web service from setting the content-type using my wrapper:
public class IE8FilterResponseWrapper extends HttpServletResponseWrapper {
public IE8FilterResponseWrapper(HttpServletResponse response) {
super(response);
}
public void forceContentType(String type) {
super.setContentType(type);
}
public void setContentType(String type) {
}
public void setHeader(String name, String value) {
if (!name.equals("Content-Type")) {
super.setHeader(name, value);
}
}
public void addHeader(String name, String value) {
if (!name.equals("Content-Type")) {
super.addHeader(name, value);
}
}
public String getContentType() {
return super.getContentType();
}
}
And my filter now looks like:
public class IE8Filter implements Filter {
private Logger logger = LoggerHelper.getLogger();
#Override
public void destroy() {}
#Override
public void doFilter(ServletRequest req, ServletResponse res,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
String userAgent = request.getHeader("User-Agent");
logger.debugf("User Agent = '%s'", userAgent);
IE8FilterResponseWrapper wrapper = new IE8FilterResponseWrapper(response);
if (userAgent.contains("MSIE 8") || userAgent.contains("MSIE 7")) {
wrapper.forceContentType("text/html");
chain.doFilter(req, wrapper);
}
else {
chain.doFilter(req, res);
}
}
#Override
public void init(FilterConfig arg0) throws ServletException {}
}
I'm not sure if this was how wrappers were intended to be used but heck it works.