I want to write a code like this:
try {
try {
someStuffThatCausesBusinessExceptions();
} finally {
try {
cleanUp();
} catch (Exception e) {
// I don't really care
}
}
} catch (BusinessLogicException e) {
// work with exception
// cleaning up must be done by that point (or at least tried to)
}
Will exceptions from business logic survive the possible hiatus during cleanUp? Is there a better way to ignore all the possible exceptions from cleanUp?
A catch block will only catch Throwables that were thrown in its corresponding try block. Thus, your exceptions thrown in the surrounding try block will be preserved and caught in the outer catch block.
Yes. Your exception will reach the last catch. However, this structure seems weird an non-idiomatic to me, i guess i would even prefer having cleanUp() more than once in that code over having 3 tries.
There are two cases-:
1. if excetpion occurs from mehtod someStuffThatCausesBusinessExceptions only then it will be caught in your outer catch block.
2. if the methods someStuffThatCausesBusinessExceptions and cleanUp both throw exceptions then the exception thrown from try block is suppressed.
Yes!! there is better way.You can use try-with-resources statement.
Please refere to this link.
https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html
Related
This question already has answers here:
Why do we use finally blocks? [duplicate]
(11 answers)
Closed 5 years ago.
Consider the code
try{
//code
} catch(Exception e) {
// handle
} finally {
// close open connections
}
and this
try{
//code
} catch(Exception e) {
// handle
}
// close open connections
since both are same what is the necessity of finally block?
The finally block will always be executed, even if you don't catch all the exceptions thrown by the try block in the catch block, or if the catch block throws a new exception.
In the second snippet, the code following the try-catch block won't be executed if either the try or catch blocks throw exceptions not caught by the catch block.
A finally block is much safer, as it's guaranteed to execute even if your try block throws an exception that isn't handled by the catch block or returns.
It also has the side effect of organizing all the "cleanup" code in an expected location, making the code (arguably) easier to maintain.
It's worth noting, by the way, that if you're using Java 7 or higher, and the resource you're handling is an AutoCloseable (such as a java.sql.Connection, for example), there's an even cleaner solution - the try-with-resource syntax, which saves you the hassle of explicitly closing the resource:
try (Connection con = /* something */) {
// code
} catch (SomeException e) {
// handle
// If there's nothing intelligent to do, this entire clause can be omitted.
}
finally block is used to execute important code such as closing connection, stream etc. finally block in java can be used to put "cleanup" code such as closing a file, closing connection etc.
Java finally block is always executed whether exception is handled or not.
For each try block there can be zero or more catch blocks, but only one finally block.
The finally block will not be executed if program exits(either by calling System.exit() or by causing a fatal error that causes the process to abort).
Can we write any implementation code in catch block? What are the rules to be used to implement in catch block?
try{
resultado = (T) mensaje.getBody(clase);
}
catch(Exception ex){
resultado = null;
this.destruye();
throw ex;
}
You can write all the code you want in your catch block.
Exception handlers can do more than just print error messages or halt
the program. They can do error recovery, prompt the user to make a
decision, or propagate the error up to a higher-level handler using
chained exception
Remember, this code will only be executed if an exception is thrown.
Yes you can write any code you want in the catch block, as you can see in the catch Blocks Documentation:
The catch block contains code that is executed if and when the exception handler is invoked.
So here the catch block is only executed if the code inside the try block raises an exception, so in that case you can handle the Exception and write whatever code you want.
For example you can write:
Int input = 0;
try {
System.out.println("Enter a number :");
input = scanner.nextInt();
} catch (IOException e) {
System.err.println("Caught IOException: " + e.getMessage());
System.out.println("Rewrite the number please");
}
And to answer you question about "What are the rules to be used to implement in catch block?" and if it's a bad practice to write code in the catch block:
You can see in the documentation that:
Exception handlers can do more than just print error messages or halt the program. They can do error recovery, prompt the user to make a decision, or propagate the error up to a higher-level handler using chained exceptions, as described in the Chained Exceptions section.
So it's fine to write whatever code you need to write in the catch block, you can take a look at Exception Chaining to see that you can write code there, but keep in mind that it's made to write code that handles the given Exception.
Can we write any implementation code in catch block?
You can write whatever code you want in your catch block. The code will only be executed only when the exception is thrown.
What are the rules to be used to implement in catch block?
Ideally catch blocks contain code which deal with the exceptions for an instance printing stack trace, log the exception, forwarding the flow to a jsp or a method, wrapping the exception & rethrowing it, exit gracefully. Besides this you can write whatever code as per your requirement you don't have to follow any specific rules.
Yes, you can write whatever you want....
If you think that your code porting may be arise any error
for that reason the program have terminated in that case to handle that exception you have to used catch block so that the program will not terminate.
try{
/h/ere code arise exception
}
catch(this is place where Exeption class which hold the exception type throw object){
//here for handling the exception
}
I am working on a java program that will be constructed by multiple methods, each with it's own try/catch blocks. I find myself duplicating the same catch block in each try block.
Is there any way to have multiple try blocks use a single catch block?
Thanks
put the shared logic in a common method and invoke it from each catch block.
try {
try (BufferedReader autoClosable1 = new BufferedReader(new FileReader(new File("")))) {
}
try (BufferedReader autoClosable2 = new BufferedReader(new FileReader(new File("")))) {
}
} catch (Exception e) {
e.printStackTrace();
}
//try it in java 7 onwards..
I don't believe you can have multiple try declarations going off of one catch, but depending on the situation, you probably don't need it.
If the code you're writing throws the same exception, then it can all be handled in one try...catch statement. Place all dodgy code within the try block and handle the exception that comes through.
If the code you're writing throws different exceptions, then with Java 7, you can catch multiple exceptions within one catch block. You'd still place the dodgy code in the one try block.
No you can not do that. You have to have at least one catch block or a finally block in order the try block to be compiled. Since the finally block is anyway going to be executed no matter exception occurred or not you have to have catch block in case to handle the exception occurred. As the jtah says you can have a common method to be executed in each catch block.
for sql connection we generally do like the following way
Class.forName("com.mysql.jdbc.Driver");
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/test","username","password");
As this throws exception so we generally write inside try block.But my question if i write unnecessary codes that does not throws exception with in try block then will the performance gets effected?
try
{
//some 100 lines codes that does not throw exception
Class.forName("com.mysql.jdbc.Driver");
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/test","username","password");
}
catch(Exception e)
{
}
No, at least not in any meaningful way. The biggest harm in having a "too big" try block is readability and in most cases it doesn't make sense. You could just have a throws SQLException in the method instead of a try block that spans most of the method.
Don't think so.
Its good practice to save your application from crashes.
But idea is to do not blindly use Exception but exception refer to your try{}.
In your case:
try{
//...
}
catch (ClassNotFoundException e) {
}
catch(SQLException e)
{
}
If I write unnecessary codes that does not throws exception with in try block then will the performance gets effected?
Answer is no .
Having code in try-blocks should have basically zero performance effect. The real hit comes when an exception is actually thrown.
Read these SO questions
1.Java try/catch performance, is it recommended to keep what is inside the try clause to a minimum?
2.Try Catch Performance Java
This question already has answers here:
Why do we use finally blocks? [duplicate]
(11 answers)
Closed 5 years ago.
Why do this
} catch (SQLException sqle) {
sqle.printStackTrace();
} finally {
cs.close();
rs.close();
}
Instead of this
} catch (SQLException sqle) {
sqle.printStackTrace();
}
rs.close();
cs.close();
Because if an exception gets thrown no code after the try block is executed unless the exception is caught. A finally block is always executed no matter what happens inside your try block.
Look at your catch block - it's going to throw DAOException. So the statements after your catch block aren't going to be executed even in the sample you've given. What you've shown (wrapping one exception in another) is one common pattern - but another possibility is that the catch block "accidentally" throws an exception, e.g. because one of the calls it makes fails.
Additionally, there may be other exceptions you don't catch - either because you've declared that the method throws them, or because they're unchecked exceptions. Do you really want to leak resources because an IllegalArgumentException got thrown somewhere?
Because if an exception is thrown,
Code in the finally clause will execute as the exception propagates outward, even if the exception aborts the rest of the method execution;
Code after the try/catch block will not get executed unless the exception is caught by a catch block and not rethrown.
According to HeadFirst Java, a finally block will run even if the try or catch block has a return statement. Flow jumps to finally and then back to return.
Because it ensures that the stuff in the finally block gets executed. Stuff after catch might not get executed, say, for example, there is another exception in the catch block, which is very possible. Or you just do what you did, and throw an exception wrapping the original exception.
The finally keyword guarantees that the code is executed. In your bottom example, the close statements are NOT executed. In the top example, they are executed (what you want!)
Your second approach won't do the 'close' statements because it is already left the method.
This is the way to avoid resource leaks
If you catch all errors, there should no difference, otherwise, only code inside finally block is executed because the code execution sequence is:
finally code -> error throw -> code after catch
hence, once your code throw any unhandled error, only finally code block works as expected.
The code in the finally block will get called before the exception is rethrown from the catch block. This ensures that any cleanup code that you've put in the finally block gets called. Code outside of the finally block will not be run.
this might clarify: http://www.java2s.com/Code/Java/Language-Basics/Finallyisalwaysexecuted.htm
consider the catch can throw an exception to the higher level functions in the call stack. This will lead calling final before throwing the exception to the upper level.
In http://docs.oracle.com/javase/tutorial/essential/exceptions/finally.html this is misleading (and may have originated the question):
The try block of the writeList method that you've been working with here opens a PrintWriter. The program should close that stream before exiting the writeList method. This poses a somewhat complicated problem because writeList's try block can exit in one of three ways.
1. The new FileWriter statement fails and throws an IOException.
2. The list.get(i) statement fails and throws an IndexOutOfBoundsException.
3. Everything succeeds and the try block exits normally.
The 4th way (an exception other than IOException and IndexOutOfBoundsException is thrown) is missing. The code depicted in the preceding page only catches (1) and (2) before resorting to finally.
I'm also new to Java and had the same questioning before finding this article. Latent memory tend to attach itself more to examples than to theory, in general.
The finally block may not always run, consider the following code.
public class Tester {
public static void main(String[] args) {
try {
System.out.println("The main method has run");
System.exit(1);
} catch (Exception e) {
e.printStackTrace();
} finally {
System.out.println("The finally block has run");
}
}
}
In your case, I would suggest to wrap the code inside finally block into try/catch, as this code apparently may throw an exception.
} catch (SQLException sqle) {
sqle.printStackTrace();
} finally {
try {
cs.close();
rs.close();
} catch (Exception e) {
//handle new exception here
}