Many I/O resources in Java such as InputStream and OutputStream need to be closed when they are finished with, as discussed here.
How can I search my project for places where such resources are not being closed, e.g. this kind of error:
private void readFile(File file) throws IOException {
InputStream in = new FileInputStream(file);
int nextByte = in.read();
while (nextByte != -1) {
// Do something with the byte here
// ...
// Read the next byte
nextByte = in.read();
}
// Oops! Not closing the InputStream
}
I've tried some static analysis tools such as PMD and FindBugs, but they don't flag the above code as being wrong.
An I/O Stream represents an input source or an output destination. A stream can represent many different kinds of sources and destinations, including disk files, devices, other programs, and memory arrays.
Bad things that can happen when you don't close your streams: you can run out of file handles. data that you think is written to disk may still be in the buffer (only) files might still be locked for other processes (depends on the platform)
In Java, streams are the sequence of data that are read from the source and written to the destination. An input stream is used to read data from the source. And, an output stream is used to write data to the destination. class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"
There are two basic types of stream defined by Java, called byte stream and character stream. The byte stream classes provide a convenient means for handling input and output of bytes and character streams provide a convenient means for handling input and output of characters, respectively.
It's probably matter of setting - I ran FindBugs through my IDE plugin and it reported OS_OPEN_STREAM.
If FindBugs with modified rules doesn't work for you, another slower approach is heap analysis. VisualVM allows you to query all objects of a specific type that are open at any given time within a heap dump using OQL. You could then check for streams open to files that shouldn't be accessed at that point in the program.
Running it is as simple as:
%>jvisualvm
Choose the running process. Choose option save heap dump (or something to that effect), open the heap dump and look at class instances for file streams in the browser, or query for them.
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