try-with-resources – Page 2

Transaction rollback on SQLException using new try-with-resources block

April 1, 2023 by Tarik

According to the language spec, the connection will be closed before the catch clause is executed (http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.20.3.2). A possible solution is to nest try-with-resources statements: try (java.sql.Connection con = createConnection()) { con.setAutoCommit(false); try (Statement stm = con.createStatement()) { stm.execute(someQuery); // causes SQLException } catch(SQLException ex) { con.rollback(); con.setAutoCommit(true); throw ex; } con.commit(); con.setAutoCommit(true); } Hopefully … Read more

What’s the purpose of try-with-resources statements?

March 26, 2023 by Tarik

It was introduced because of some resources used in Java (like SQL connections or streams) being difficult to be handled properly; as an example, in java 6 to handle a InputStream properly you had to do something like: InputStream stream = new MyInputStream(…); try { // … use stream } catch(IOException e) { // handle … Read more

8 branches for try with resources – jacoco coverage possible?

March 21, 2023 by Tarik

Well I can’t tell you what the exact problem with Jacoco is, but I can show you how Try With Resources is compiled. Basically, there are a lot of compiler generated switches to handle exceptions thrown at various points. If we take the following code and compile it public static void main(String[] args){ String a … Read more

Why write Try-With-Resources without Catch or Finally?

March 13, 2023 by Tarik

As explained above this is a feature in Java 7 and beyond. try with resources allows to skip writing the finally and closes all the resources being used in try-block itself. As stated in Docs Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource. See this … Read more

Try-with-resources and return statements in java

March 5, 2023 by Tarik

Based on Oracle’s tutorial, “[the resource] will be closed regardless of whether the try statement completes normally or abruptly”. It defines abruptly as from an exception. Returning inside the try is an example of abrupt completion, as defined by JLS 14.1.

Why does try-with-resource require a local variable?

March 1, 2023 by Tarik

The link in the comment by @McDowell reveals the correct answer in a blog post comment by Joe Darcy who led the Java Technology Specification that introduced the try-with-resources statement: Back in JDK 7, we started with a try-with-resources construct like that allowed a general expression to be used for the resource, including a method … Read more

Close multiple resources with AutoCloseable (try-with-resources)

February 14, 2023 by Tarik

Try with resources can be used with multiple resources by declaring them all in the parenthesis. See the documentation Relevant code excerpt from the linked documentation: public static void writeToFileZipFileContents(String zipFileName, String outputFileName) throws java.io.IOException { java.nio.charset.Charset charset = java.nio.charset.StandardCharsets.US_ASCII; java.nio.file.Path outputFilePath = java.nio.file.Paths.get(outputFileName); // Open zip file and create output file with // try-with-resources … Read more

What is a suppressed exception?

January 23, 2023 by Tarik

To clarify the quote in Jon’s answer, only one exception can be thrown by a method (per execution) but it is possible, in the case of a try-with-resources, for multiple exceptions to be thrown. For instance one might be thrown in the block and another might be thrown from the implicit finally provided by the … Read more

Am I using the Java 7 try-with-resources correctly

January 22, 2023 by Tarik

It’s correct and there’s no requirement for catch clause. Oracle java 7 doc says the resource will be closed regardless of whether an exception is actually thrown or not. You should use a catch clause only if you want to react upon the exception. The catch clause will be executed after the resource is closed. … Read more

How should I use try-with-resources with JDBC?

November 15, 2022 by Tarik

I realize this was long ago answered but want to suggest an additional approach that avoids the nested try-with-resources double block. public List<User> getUser(int userId) { try (Connection con = DriverManager.getConnection(myConnectionURL); PreparedStatement ps = createPreparedStatement(con, userId); ResultSet rs = ps.executeQuery()) { // process the resultset here, all resources will be cleaned up } catch (SQLException … Read more