RFR: 4799358: BufferOutputStream.write() should immediately throw IOExcept on closed stream

[Vyom Tewari]

With the current  implementation of BufferedOutputStream if you close the stream and try to write to the closed stream BufferedOutputStream does not throw an IOException until the internal buffer is full. To fix this issue i added a private  "ensureOpen" function to BufferedOutputStream which will check if the underline stream is open. If the underline stream is closed "ensureOpen" will throw the IOException.

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Commit messages:
 - 4799358: BufferOutputStream.write() should immediately throw IOException on closed stream

Changes: https://git.openjdk.org/jdk/pull/15361/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15361&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-4799358
  Stats: 75 lines in 3 files changed: 75 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15361.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15361/head:pull/15361

PR: https://git.openjdk.org/jdk/pull/15361