Java: try with AutoCloseable resources

1. Multiple AutoCloseable resources

  try (InputStream in = getInputStream(); OutputStream out = getOutputStream()) {
      ... ...
  }
  

The resources are closed in the reverse order of declaration.

2. Resource leaking caused by nested constructors

There is possible resource leaking issue for the code below:

  try(InputStream in = new MyFilterInputStream(new BufferedInputStream(new FileInputStream("/tmp/test.file")))) {
      ... ...
  }
  

Because any checked exception from the chain of the constructors can cause resource failing to close. The code below with multiple declared AutoCloseables should be used:

  try(FileInputStream fis = new FileInputStream("/tmp/test.file");
      BufferedInputStream bis = new BufferedInputStream(fis);
      MyFilterInputStream mfis = new MyFilterInputStream(bis)) {
      ... ...
  }
  

3. What will happen if the AutoCloseable is null

A resource is closed only if it initialized to a non-null value. So the code works without having to worry about NPE when in is null.

  try(InputStream in = createNew==true? createInputStream(): null) {
      if(in==null) {
          ... ...
      }
  }
  

see also

• Correct idiom for managing multiple chained resources in try-with-resources block?