Develop Reference

How to extract try catch outside method?

I have this method sendParameterValueAsMQTTMessage() which I use to publish message via MQTT on a specific topic. I am using try catch two times after another (not nested) but it still seems somewhat ugly and overcrowding the method. I read an article on clean code where Uncle Bob talks about extracting the body of try catch but I seem to not grasp it quite well or at least not in my case.
How could I get rid of the try catch in my method by extracting it outside?
public void sendParameterValueAsMQTTMessage() {
String payload = null;
try {
payload = convertToJSONString("range", String.valueOf(range));
} catch (JSONException e) {
this.logger.log(Level.ERROR, e);
}
MQTTMessage message = new MQTTMessage(MQTTTopics.RANGE_TOPIC,payload,0);
try {
this.client.publish(message);
Thread.sleep(3000);
} catch (Exception e) {
this.logger.log(Level.ERROR, e);
}
}

there are multiple different problems with provided code, here is how I'd refactor it:
public void sendParameterValueAsMQTTMessage() {
final String payload = tryGetPayloadAsJson();
if (payload != null) {
trySendPayloadViaMQTT(payload);
}
}
private String tryGetPayloadAsJson() {
try {
return convertToJSONString("range", String.valueOf(range));
} catch (JSONException e) {
this.logger.log(Level.ERROR, e);
}
return null;
}
private void trySendPayloadViaMQTT(final String payload) {
try {
final MQTTMessage message = new MQTTMessage(MQTTTopics.RANGE_TOPIC, payload, 0);
this.client.publish(message);
Thread.sleep(3000);
} catch (Exception e) {
this.logger.log(Level.ERROR, e);
}
}
one thing which might be improved here based on Uncle Bob's advice is to actually move try/catch outside of trySendPayloadViaMQTT, like this:
public void sendParameterValueAsMQTTMessage() {
final String payload = tryGetPayloadAsJson();
if (payload != null) {
trySendPayloadViaMQTT(payload);
}
}
private String tryGetPayloadAsJson() {
try {
return convertToJSONString("range", String.valueOf(range));
} catch (JSONException e) {
this.logger.log(Level.ERROR, e);
}
return null;
}
private void trySendPayloadViaMQTT(final String payload) {
try {
sendPayloadViaMQTT(payload);
} catch (Exception e) {
this.logger.log(Level.ERROR, e);
}
}
private void sendPayloadViaMQTT(final String payload) {
final MQTTMessage message = new MQTTMessage(MQTTTopics.RANGE_TOPIC, payload, 0);
this.client.publish(message);
Thread.sleep(3000);
}

you can put all of your code in just one try block and set multiple catches, when ever an exception be happened, the catch that is revelated to it will be execute, like:
try{
int a[]=new int[5];
a[5]=30/0;
}
catch(ArithmeticException e)
{
System.out.println("Arithmetic Exception occurs");
}
catch(ArrayIndexOutOfBoundsException e)
{
System.out.println("ArrayIndexOutOfBounds Exception occurs");
}

You can use single general catch for both possible exceptions inside the method as following:
public void sendParameterValueAsMQTTMessage() {
String payload = null;
try {
payload = convertToJSONString("range", String.valueOf(range));
MQTTMessage message = new MQTTMessage(MQTTTopics.RANGE_TOPIC,payload,0);
this.client.publish(message);
Thread.sleep(3000);
} catch (Exception e) {
this.logger.log(Level.ERROR, e);
}
}

public void sendParameterValueAsMQTTMessage() {
String payload = null;
try {
payload = convertToJSONString("range", String.valueOf(range));
} catch (JSONException e) {
this.logger.log(Level.ERROR, e);
}
MQTTMessage message = new MQTTMessage(MQTTTopics.RANGE_TOPIC,payload,0);
publishMessage(message); //extracted in a new method
}
public void publishMessage(MQTTMessage message){
try {
this.client.publish(message);
Thread.sleep(3000);
} catch (Exception e) {
this.logger.log(Level.ERROR, e);
}
}

How could I deal with this custom Exception?

I have this bit of code which depends from a custom Exception thrown by a function inside findID() it throws a NoClientFound Exception that I made whenever this mentioned function returns a null (The client does not exist).
The IDE suggests that I shall apply that Exception into the code, but in this bit of code, where I need the ID to be null (unique IDs) I "can't catch that exception" since if I catch it, the function will not be executed as intended.
Question: How I can manage this?
Function with the Exception problem
public boolean add(Client c) {
StringBuilder sb = new StringBuilder();
boolean added = false;
try {
if (findID(c.getID()) == null) {
try (BufferedWriter bw = new BufferedWriter(
new FileWriter(fitxer, true));) {
//Add client to file
bw.write(sb.append(c.getID()).append(SEPARADOR).
append(c.getName()).toString());
bw.newLine();//New line
bw.flush(); //Push to file
added = true;
} catch (IOException e) {
Logger.getLogger(DaoClient.class.getName()).log(Level.SEVERE,
null, "Error appeding data to file" + e);
}
}
} catch (IOException ex) {
Logger.getLogger(DaoClient.class.getName()).log(Level.SEVERE, null,
"Error appeding data to file" + ex);
} finally {
}
return addded;
}
Exception Code
public class NoClientFound extends Exception {
private String msg;
public NoClientFound() {
super();
}
public NoClientFound(String msg) {
super(msg);
this.msg = msg;
}
#Override
public String toString() {
return msg;
}

You can catch that exception and handle it accordingly. When you catch NoClientFound exception that means findID(c.getID()) is null. So without handling that in the if block you can handle that within the catch block.
public boolean add(Client c) {
StringBuilder sb = new StringBuilder();
boolean added = false;
try {
// call the function
findID(c.getID());
} catch (NoClientFound ex) {
//handle the NoClientFound exception as you like here
BufferedWriter bw = new BufferedWriter(
new FileWriter(fitxer, true));
//Add client to file
bw.write(sb.append(c.getID()).append(SEPARADOR).
append(c.getName()).toString());
bw.newLine();//New line
bw.flush(); //Push to file
added = true;
}catch (IOException ex) {
Logger.getLogger(DaoClient.class.getName()).log(Level.SEVERE, null,
"Error appeding data to file" + ex);
}finally {
}
return addded;
}

I assume you already have a null check on findID(...)
if( c == null || findID(c.getID()) == null){
throw new NoClientFound("Client not found!");
}else{
//add your file writing operation
}
and Also in NoClientFound class extend it from RuntimeException, not the Exception.
public class NoClientFound extends RuntimeException {
...
}
Caller method:
public void caller(){
Client client = new Client();
client.setId(1);
...
try{
add(client);
}catch(NoClientFound ex){
//client not found then create one for ex...
}
catch(Exception ex){
//somthing else happend
log.error(ex.getmessge());
}
}

Missing return statement, what i am missing

I written a method which will acknowledge the controller by returning true and false, I return true inside try if everything goes fine it will return true and I return false inside catch blocks, but still method shows me error "missing return statement" what is the best way to do it.
The below method written in java will send back the true or false to the controller.
Secondly I want to carry the exception message from here to controller, I think of returning string, is it good approach,
Kindly suggest me the best way to do the exception handling
public boolean pickSalayData(String yearMonth, String regionId, String circleId, Userdetail loginUser) throws MyExceptionHandler {
String tableSuffix = yearMonth.substring(4, 6) + yearMonth.substring(0, 4);
log.info("Pick Salary Data From ERP " + DateUtility.dateToStringDDMMMYYYY(new Date()));
List<SalaryDetailReport> detailReports = hRMSPickSalaryDataDAO.findAll(yearMonth, regionId, circleId);
TransactionDefinition def = new DefaultTransactionDefinition();
TransactionStatus trstatus = transactionManager.getTransaction(def);
try {
List<SalaryDetailReport> salaryDetailReport = null;
int countDetail = 0;
if (detailReports != null && detailReports.size() > 0) {
for (SalaryDetailReport salary : detailReports) {
try {
if (countDetail % COMMIT_COUNT == 0) {
if (salaryDetailReport != null) {
salaryDetailReportDAO.save(salaryDetailReport, tableSuffix);
reportHistoryDAO.save(salaryDetailReport, loginUser);
}
salaryDetailReport = new ArrayList<SalaryDetailReport>();
}
salaryDetailReport.add(salary);
countDetail++;
} catch (Exception e) {
log.error("Error on Save Salary Pay Head Details Data from ERP to Prayas .");
}
}
if (salaryDetailReport != null && salaryDetailReport.size() > 0) {
salaryDetailReportDAO.save(salaryDetailReport, tableSuffix);
reportHistoryDAO.save(salaryDetailReport, loginUser);
}
} else {
throw new MyExceptionHandler("No record for Save in Database from ERP.");
}
salaryDetailReportDAO.update(tableSuffix, regionId, circleId);
List<SalaryDetailReport> reports = salaryDetailReportDAO.findAll(tableSuffix, regionId, circleId);
if (reports != null && reports.size() > 0) {
for (SalaryDetailReport salaryDetail : reports) {
try {
SalaryDetail sd = new SalaryDetail();
sd.setDetailReport(salaryDetail);
salaryDetailDAO.save(sd, tableSuffix);
} catch (Exception e) {
log.error("Error occured", e);
e.printStackTrace();
throw new MyExceptionHandler(" Error :" + e.getMessage());
}
}
System.out.println("data found");
} else {
log.error("Salary Record Not Found.");
throw new MyExceptionHandler("No record Found.");
}
salaryDetailDAO.updateEarningDeduction(tableSuffix);
//salaryDetailDAO.updateEarningDeductionsInSDT();
transactionManager.commit(trstatus);
try {
hRMSPickSalaryDataDAO.update(regionId, circleId, yearMonth);
return true;
} catch (Exception ex) {
log.error("Some error : ", ex);
}
// // System.out.println("Completed =============================");
} catch (MyExceptionHandler ex) {
transactionManager.rollback(trstatus);
ex.printStackTrace();
log.error("Failed to Save Salary data :" + ex.getMessage());
return false;
} catch (Exception ex) {
transactionManager.rollback(trstatus);
ex.printStackTrace();
log.error("Error occured on Save Salary data.", ex);
return false;
}
}

You are missing return statement for the following catch block :
catch (Exception ex) {
log.error("Some error : ", ex);
}
Either you add return statement in this catch block or at the end of mehtod

If this code throws an Exception, then the following catch code will not be entered into and hence there is no return value
try {
hRMSPickSalaryDataDAO.update(regionId, circleId, yearMonth);
return true;
} catch (Exception ex) {
log.error("Some error : ", ex);
**edit**
return `true||false`;
}
} catch (...) {
return something;
}

SSH connection leaving stale sessions on the server

I am programatically trying to connect to ssh running remotely. I am running a tomcat server instance. Whenever i need, from the code, i create a session, connect and execute a few commands that are needed within a try block and then close off the connection that was created as part of the finally block at all the places. Things work well and fine, but at some cases when i execute a w or netstat command on the ssh server, I see a few connections that are idle for more than a few hours and the ip address of those connections shows the connection to be from my application, but my java heap dump does not show any instance of my class in the memory, but i see ganymed related class instances in the heap.
I am using ganymed-ssh-260 library to connect to my server.
Is this something that someone has already seen?
Attaching the code snippet that connectes the ssh to the server
public class SSHExecutor{
private OutputStream stdin;
private InputStream stdout;
private InputStream stderr;
private Session sess;
private Connection conn;
public void createConnection(String hostname, int port, String userName, String password) throws Exception {
try {
conn = new Connection(hostname, port);
final boolean isAuthenticated = publicKeyAccess(hostname, userName, password);
if (!isAuthenticated) {
throw new IOException("Authentication failed.");
}
sess = conn.openSession();
final int xWidth = 90;
final int yWidth = 80;
sess.requestPTY("dumb", xWidth, yWidth, 0, 0, null);
sess.startShell();
stdin = sess.getStdin();
stdout = sess.getStdout();
stderr = sess.getStderr();
isConnectionActive = true;
final String response = getResponse();
if (response != null && response.toLowerCase().contains(ObjectConstants.CURRENTLY_NOT_AVAILABLE)) {
throw new IOException("Account is currently not available.");
}
} catch (Exception e) {
log.error("Problem in CreateConnection", e);
isConnectionActive = false;
throw e;
}
}
public String getResponse() {
final StringBuffer responseData = new StringBuffer();
try {
final int byteValue = 8192;
final byte[] buffer = new byte[byteValue];
try {
while (true) {
if ((stdout.available() == 0) && (stderr.available() == 0)) {
int conditions = 1;
if (promptString != null && promptString.length() > 0) {
final int fiveThousand = 5000;
conditions = sess.waitForCondition(ChannelCondition.STDOUT_DATA
| ChannelCondition.STDERR_DATA | ChannelCondition.EOF, fiveThousand);
} else {
conditions = sess.waitForCondition(ChannelCondition.STDOUT_DATA
| ChannelCondition.STDERR_DATA | ChannelCondition.EOF,
ObjectConstants.THOUSAND_FIVE_HUNDRED);
}
if ((conditions & ChannelCondition.TIMEOUT) != 0) {
break;
}
if ((conditions & ChannelCondition.EOF) != 0) {
if ((conditions & (ChannelCondition.STDOUT_DATA | ChannelCondition.STDERR_DATA)) == 0) {
break;
}
}
}
while (stdout.available() > 0) {
final int len = stdout.read(buffer);
if (len > 0) {
responseData.append(new String(buffer, 0, len));
}
}
while (stderr.available() > 0) {
final int len = stderr.read(buffer);
if (len > 0) {
responseData.append(new String(buffer, 0, len));
}
}
if (promptString != null && promptString.length() > 0) {
if (responseData.indexOf(promptString) != -1) {
break;
}
}
}
} catch (Exception e) {
log.error("Read Error :", e);
}
} catch (Exception e) {
log.error("getResponse Error ", e);
}
return responseData.toString();
}
public String executeCommand(String command) throws IOException {
String response = null;
if (isConnectionActive && stdin != null) {
try {
stdin.write(command.getBytes());
stdin.flush();
response = getResponse();
} catch (IOException ie) {
throw ie;
} catch (Exception e) {
log.error("Exception in executeCommandForPage()", e);
response = e.getMessage();
}
} else {
response = "Connection not active.";
}
return response;
}
public void closeConnection() {
if (stderr != null) {
try {
stderr.close();
} catch (Exception e) {
log.error("Exception in closeConnection()", e);
}
}
if (stdout != null) {
try {
stdout.close();
} catch (Exception e) {
log.error("Exception in closeConnection()", e);
}
}
if (stdin != null) {
try {
stdin.close();
} catch (Exception e) {
log.error("Exception in closeConnection()", e);
}
}
if (sess != null) {
try {
sess.close();
} catch (Exception e) {
log.error("Exception in closeConnection()", e);
}
}
if (conn != null) {
try {
conn.close();
} catch (Exception e) {
log.error("Exception in closeConnection()", e);
}
}
}
}

You're creating a local Connection variable but you're testing what must be a member variable, which is always null, so you're never closing it.
If authentication fails you're leaking the connection.

Get detail messages of chained exceptions Java

I'd like to know how I could throw a "final" Exception, containing a detailed message with all the detailed messages of a number of chained exceptions.
For example suppose a code like this:
try {
try {
try {
try {
//Some error here
} catch (Exception e) {
throw new Exception("FIRST EXCEPTION", e);
}
} catch (Exception e) {
throw new Exception("SECOND EXCEPTION", e);
}
} catch (Exception e) {
throw new Exception("THIRD EXCEPTION", e);
}
} catch (Exception e) {
String allMessages = //all the messages
throw new Exception(allMessages, e);
}
I'm not interested in the full stackTrace, but only in the messages, I wrote. I mean, I'd like to have a result like this:
java.lang.Exception: THIRD EXCEPTION + SECOND EXCEPTION + FIRST EXCEPTION

I think what you need is:
public static List<String> getExceptionMessageChain(Throwable throwable) {
List<String> result = new ArrayList<String>();
while (throwable != null) {
result.add(throwable.getMessage());
throwable = throwable.getCause();
}
return result; //["THIRD EXCEPTION", "SECOND EXCEPTION", "FIRST EXCEPTION"]
}

you can better use it this way, merge the message() of previous Exception with the message() of new Exception you are throwing:
} catch (Exception e) {
throw new Exception("FIRST EXCEPTION" + e.getMessage(), e);
}

Cycle through the exception cause and append the message in each exception.
try
{
try
{
try
{
try
{
throw new RuntimeException("Message");
}
catch (Exception e)
{
throw new Exception("FIRST EXCEPTION", e);
}
}
catch (Exception e)
{
throw new Exception("SECOND EXCEPTION", e);
}
}
catch (Exception e)
{
throw new Exception("THIRD EXCEPTION", e);
}
}
catch (Exception e)
{
String message = e.getMessage();
Throwable inner = null;
Throwable root = e;
while ((inner = root.getCause()) != null)
{
message += " " + inner.getMessage();
root = inner;
}
System.out.println(message);
}
Which prints
THIRD EXCEPTION SECOND EXCEPTION FIRST EXCEPTION Message

You can just add the previous exception message on each exception
This is an example :
public static void main(String[] args) {
try {
try {
try {
try {
throw new Exception();
// Some error here
} catch (Exception e) {
throw new Exception("FIRST EXCEPTION", e);
}
} catch (Exception e) {
Exception e2 = new Exception("SECOND EXCEPTION + " + e.getMessage());
throw e2;
}
} catch (Exception e) {
Exception e3 = new Exception("THIRD EXCEPTION + " + e.getMessage());
throw e3;
}
} catch (Exception e) {
System.out.println(e);
}
}
The result is : java.lang.Exception: THIRD EXCEPTION + SECOND EXCEPTION + FIRST EXCEPTION

Here is a nice utility for converting chained exceptions to string:
public final class ThrowableUtil {
private ThrowableUtil() {}
public static String chainedString(#NonNull Throwable throwable) {
StringBuilder SB = new StringBuilder(throwable.toString());
while((throwable = throwable.getCause()) != null)
SB.append("\ncaused by ").append(throwable);
return SB.toString();
}
public static String chainedString(#NonNull String msg, #NonNull Throwable throwable) {
StringBuilder SB = new StringBuilder(msg);
do {
SB.append("\ncaused by ").append(throwable);
} while((throwable = throwable.getCause()) != null);
return SB.toString();
}
}
Example output:
ThrowableUtil.chainedString(e);
produces
java.io.IOException: Failed to create required video encoder
caused by java.lang.RuntimeException: Invalid mime type
Another example output:
ThrowableUtil.chainedString("Writing of media file failed", e);
produces
Writing of media file failed
caused by java.io.IOException: Failed to create required video encoder
caused by java.lang.RuntimeException: Invalid mime type

I had saved all attributes in a class object with the following example:
public List<ErrorMessage> getMessageList(Throwable throwable) {
List<ErrorMessage> errorMessageList = new ArrayList<ErrorMessage>();
while (throwable != null) {
ErrorMessage message = new ErrorMessage();
message.set_message( throwable.getMessage());
message.set_line(throwable.getStackTrace()[0].getLineNumber());
message.set_methodName(throwable.getStackTrace()[0].getMethodName());
message.set_fileName(throwable.getStackTrace()[0].getFileName() );
message.set_className(throwable.getStackTrace()[0].getClassName());
errorMessageList.add(message);
throwable = throwable.getCause();
}
return errorMessageList;
}

Maybe simpler
try {
// code that throws exception
} catch(Throwable e ) {
var messages = new ArrayList<String>();
do {
messages.add(e.getMessage());
e = e.getCause();
} while( e!= null );
var message = String.join(" -> ", messages);
System.out.println(message);
}