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Java 'finally' clause in a nested 'try' block

Will the following finally clause be executed, if an exception is thrown by the PrintWriter?
try{
PrintWriter out = new PrintWriter(filename);
try {
//output
} finally {
out.close();
}
} catch {
//handle exception
}
If the PrintWriter throws an exception, then the nested try block will never get executed, but why the nested finally clause will still be executed, even it's nested and skipped?
Updates:
I ran some tests, if an exception is thrown before the nested try clause, that nested finally will not be executed.
If the exception is thrown inside the nested try clause, then the inner finally and the outter catch will be executed.

No because the inner try block will not be reached when an exception occurs before and therefore the finally block is not reached either.

Finally block is always executed whether exception is handled or not. Even though their is an error and it reaches to catch block, it will go to finally block to execute the piece of code.
finally block is a block that is used to execute important code such
as closing connection, stream etc.
So, Inside try{} block you placed try and finally, but you asked about the catch of outside try ,thus its not going inside the first try block.That finally wont work.
P.S. : If you put finally something like this:
try{
try{...}
finally{...}
}catch(Exception e){...}
finally{... }
//in case of exception also , the outside finally is going to work.
P.S.: Though you got your answer , but the concept is for reference of other naive programmers

An uglier variant (sometimes generated by the IDE) one sees also:
// *** UGLY
PrintWriter out = null;
try {
out = new PrintWriter(filename);
//output
} catch (IOException e) {
//handle exception
} finally {
if (out != null) {
try {
out.close();
} catch (IOException e2) {
// IGNORE
}
}
}
That explains the code a bit: as close may throw an IOException too, the code becomes cumbersome. Your code still needs nested exceptions.
With try-with-resources this can & should be written as:
try (PrintWriter out = new PrintWriter(filename)) {
//output
} catch (IOException e) {
//handle exception
} // Automatically closes.
And no longer nested exceptions.
The biggest advantage is that you need not catch any exception, and just add a throws IOException in the method signature.

Java: Poor error handling, Throw inside Finally

I have the following code which I am running through fortify. Why it gets marked for poor error handling, throw inside finally?
private String getResourceContent(String fileName) throws IOException {
try (InputStream resource = ErrorResource.classLoader.getResourceAsStream(fileName)) {
return new String(resource.readAllBytes(), StandardCharsets.UTF_8);
} catch (NullPointerException n) {
throw new ErrorDescriptorException(
String.format("Error loading Error description data from Resource file [%s].", fileName), n);
}
}

Explanation
This is explained very well in the official documentation (see Poor Error Handling: Throw Inside Finally). Let me quickly quote the important sections:
Using a throw statement inside a finally block breaks the logical progression through the try-catch-finally.
In Java, finally blocks are always executed after their corresponding try-catch blocks and are often used to free allocated resources, such as file handles or database cursors. Throwing an exception in a finally block can bypass critical cleanup code since normal program execution will be disrupted.
So you can easily bypass cleanup code by doing that, which leads to resource leaks.
Although not directly visible in your code, you actually have a hidden finally block since you are using try-with-resources which automatically closes the resource in a finally block.
Also see Throwing an exception inside finally where this was already discussed.
Example
Here is an example from the official documentation:
public void processTransaction(Connection conn) throws FileNotFoundException {
FileInputStream fis = null;
Statement stmt = null;
try {
stmt = conn.createStatement();
fis = new FileInputStream("badFile.txt");
...
} catch (FileNotFoundException fe) {
log("File not found.");
} catch (SQLException se) {
// handle error
} finally {
if (fis == null) {
// This bypasses cleanup code
throw new FileNotFoundException();
}
if (stmt != null) {
try {
// Not executed if the exception is thrown
stmt.close();
}
catch (SQLException e) {
log(e);
}
}
}
}
The call to stmt.close() is bypassed when the FileNotFoundException is thrown.
Note
Why are you checking for null using a NullPointerException instead of a basic if-else? There is rarely ever a valid reason to catch a NullPointerException. Just do:
try (InputStream resource = ErrorResource.classLoader.getResourceAsStream(fileName)) {
if (resource == null) {
// TODO Throw your exception here
}
return new String(resource.readAllBytes(), StandardCharsets.UTF_8);
}
It might also help to improve the error message by telling the exact reason that the resource could not be found.

Consider the following code, which is loosely based on yours:
String throwing(InputStream inputStream) throws IOException {
try (InputStream resource = inputStream) {
return "good";
} catch (NullPointerException n) {
return "bad";
}
}
You see, no exceptions thrown here. Still, you cannot remove the throws IOException bit – how’s that? Well, InputStream#close() can throw it, and it will be in the implicit finally block that the try-with-resources statement created. I guess there’s not much you can do about it, it looks like a Fortify false positive.

Beyond the misleading message from your tool, there is actually is poor error handling in your code, for multiple of reasons:
catching NPE is really bad practice. Either it is a bug (something that is null and shouldn't), or your code is missing a check if (whatever == null) and the corresponding code to deal with that expected situation
assuming that this NPE has exactly that meaning that you express in your new Exception is well, just guessing
In other words: without further information, it is not clear what exactly your tool complains about. But: one doesn't need a tool to understand: this is poor error handling.
Beyond that, such tools typically give some sort of information about their warnings. Meaning: there might be an "error id" coming with that warning, and you should be able to look up that "error id" in the documentation of your tool for further explanations.

Trouble in understanding the working of try-catch-finally blocks

Please correct me if I'm wrong, but, I believe that the statements in the try block get executed first, then, if any exception occurs, the statements in the finally block get executed and then the statements in the catch block get executed. If no exception occurs, then the statements in the finally block are executed once the statements in the try block are executed and the statements in the catch block are skipped.
If my above conception is not mistaken, then I don't understand why this piece of code doesn't work:
// sock is an object of the class Socket
public void run() {
try {
in = sock.getInputStream();
scan = new Scanner(in);
out = sock.getOutputStream();
pw = new PrintWriter(out);
} catch (IOException e) {
e.printStackTrace();
} finally {
sock.close();
}
}
It still says that I need to surround the statement in the finally block with try-catch.

No! the statements in the try block are executed first. Then if any exceptions occurs then the catch block statements are executed. And finally block is executed lastly. finally block gets executed even if an exception occurs in the try block. In other words if no exception occurs then first the try block is executed and then the finally block is executed.

In general If your catch block can catch the Exception thrown by the try block.
try -> finally (If No Exception)
try -> catch -> finally (If Exception)

The statements within the catch block are executed whenever an exception is encountered (which can be caught by the listed catch blocks). The statements within the finally block will always get executed, whether or not an exception was thrown within the try block.
Your sock.close(); statement could potentially throw an IOException, so either you should have another try-catch block wrapping the inner try-catch or add a throws declaration to your run() method (and the caller of the method can have a try-catch block surrounding the call).
EDIT (as per comment):
Statements within catch get executed first, then the statements within finally.

Catch Exception in finally { } ? Must?

I feel puzzle ...
I write a small routine in .jsp. Finally, ResultSet, Statement and Connection are required to be closed. I also write the closing codes in finally { }, but when the page is run, it return error that I didn't catch exception ...
I read some forum. Other people didn't catch any exception in finally { }
Any Hint ?

Sounds like you have the old problem of needing to close() in a finally block but close() throws an exception itself. Try somethig like the following...
ResultSet rs;
try {
// do various stuff
rs = ...;
} finally {
try {
if (rs != null) rs.close();
} catch (SQLException e) {
// do something with exception
}
}

You must catch exceptions in the code finally block. As you must catch exceptions in the catch block. Nested try/catches are a regular thing (albeit ugly).
One important note here is that you could have the exceptions that occur in finally declared in the throws clause of the method. However that would lead to the exception in finally overriding the original exception, which is lost. And you will see, for example, a NullPointerException, rather than FileNotFoundException.
By the way, avoid having code in the JSP file. Place it in a servlet.

finally{} doesn't do any exception catching. A finally{} block exists to make sure that certain code is run, no matter whether the try{} block reached its natural end or if it's jumping temporarily to the finally{} because an exception happened and that finally{} block was along the way. But after the finally{} finishes, the exception goes about its merry business, cavorting its way up the stack and cheerfully crashing your program.
If you want to actually catch the exception and stop it from unwinding the stack further, use catch(){}. But don't use catch blindly- catching an exception you don't actually know how to recover from is much worse than crashing, because now your program isn't working correctly and you don't have an exception stack trace telling you why.
Your ResultSet, Statement, and Connection almost certainly did get closed. And then the exception continued happening and crashed your program anyway, because that had nothing to do with your ResultSet, Statement, and Connection.
What was the actual exception?

Maybe I'm getting old, but what's wrong with catching exceptions in the catch block?

It helps if you say what is in your try block. You are probably not catching appropriate exception or your code in finally throws exception.
It is OK to have finally without catch.
try {
//do some work
}
finally {
//check of state and do clean up. You would have reached here via multiple branches.
}
It more appropriate to catch specific exceptions using catch and then handle specific cleanup there. Use finally for any code that must get executed even when exception happen.
try {
//do some work
}
catch ( RecoverableException1 re1) {
//cleanup
}
catch ( RecoverableException2 re2) {
//cleanup
}
finally {
//check of state and do clean up. You would have reached here via multiple branches.
}

finally{
try{
resultSet.close();
}catch(E e){
}finally{
try{
statement.close();
}catch(E e){
}finally{
conn.close();
}
}
}

Java exception handling

How do I use exceptions and exception handling to make my program continue even if an exception occurs while processing certain files in a set of files?
I want my program to work fine for correct files while for those files which cause an exception in program, it should ignore.
Regards,
magggi

for(File f : files){
try {
process(f); // may throw various exceptions
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
}

You have to use the try/catch/finally blocs.
try{
//Sensitive code
} catch(ExceptionType e){
//Handle exceptions of type ExceptionType or its subclasses
} finally {
//Code ALWAYS executed
}
try will allow you to execute sensitive code which could throw an exception.
catch will handle a particular exception (or any subtype of this exception).
finally will help to execute statements even if an exception is thrown and not catched.
In your case
for(File f : getFiles()){
//You might want to open a file and read it
InputStream fis;
//You might want to write into a file
OutputStream fos;
try{
handleFile(f);
fis = new FileInputStream(f);
fos = new FileOutputStream(f);
} catch(IOException e){
//Handle exceptions due to bad IO
} finally {
//In fact you should do a try/catch for each close operation.
//It was just too verbose to be put here.
try{
//If you handle streams, don't forget to close them.
fis.close();
fos.close();
}catch(IOException e){
//Handle the fact that close didn't work well.
}
}
}
Resources :
oracle.com - Lesson: Exceptions
JLS - exceptions

I guess your new to programming as execeptions are a fairly fundermental concept, as problems can happen out of your control and you need to deal with it.
The basic premise is a try catch block.
try
{
//Your code here that causes problems
}
catch(exception ex)
{
//Your code to handle the exception
}
You 'try' your code, and if an exception is raised, you 'catch' it. And do what you need.
There is also an addition to the catch block in that you can add finally{} below it. Basically even if no exception is raised the finally code is still run. You may wonder the point in this, but its often used with streams/file handling etc to close the stream.
Read more on java exceptions here in tutorials written by Sun (now Oracle)- http://download.oracle.com/javase/tutorial/essential/exceptions/
try
{
//Your code here that causes problems
}
catch(exception ex)
{
//Your code to handle the exception
}
finally
{
//Always do this, i.e. try to read a file, catch any errors, always close the file
}
The question you may ask is how do you catch different exceptions, i.e. is it a null reference, is it divide by zero, is it no file found or file not writeable etc. For this you write several different catch blocks under the try, basically one catch for each type of exception, the use of "exception" is basically a catch all statement, and like in stack of if statements if an "exception" is the first catch block it will catch everything, so if you have several catch blocks ensure exception is the last one.
Again, this is a useful but large topic so you need to read up about it.
Since you are doing multiple files, you need to basically do a loop and within the loop is contained the try/catch block.
so even if one file fails, you catch it, but carry on running, the code will then loop around onto the next file unhindered.

just catch the excpetion it may throw and do nothing with it; eat it as people say :)
But at least log it!
Very concise example:
try {
your code...
} catch (Exception e) {
log here
}

Typically, I would have done this.
ArrayList<Entry> allEntries = getAllEntries();
for(Entry eachEntry:allEntries){
try{
//do all your processing for eachEntry
} catch(Exception e{
ignoredEntries.add(eachEntry);
//if concerned, you can store even the specific problem.
} finally{
//In case of resource release
}
}
if(ignoredEntries.size() > 0){
//Handle this scenario, may be display the error to the user
}

FileSystemException may be the specific exception you are looking for.
Although, a better idea for beginners is to catch an exception and print it using
System.out.println(e);
where e is the caught exception.

public class Main
{
public static void main(String args[])
{
int a=10;
try
{
System.out.println(a/0); //Here it is not possible in maths so it goes to catch block
}
catch(ArithmeticException e)
{
System.out.println("Arithmetic Exception");
}
}
}
output:Arithmetic Exception

Exception in java are runtime error which can be handled by the program, the process is called as exception handling. Parent class of exception is Throwable.
Exception : Exception are those runtime error which can be handled by program.
Error : Those runtime error which can’nt handled by the program.
Tools used to handle Exception:
Try
Catch
Finally
Throw
Throws
more