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

Question

I know that the resource you pass with a try, will be closed automatically if the resource has AutoCloseable implemented. So far so good. But what do I do when i have several resources that I want automatically closed. Example with sockets;

try (Socket socket = new Socket()) {
    input = new DataInputStream(socket.getInputStream());
    output = new DataOutputStream(socket.getOutputStream());
} catch (IOException e) {
} 

So I know the socket will be closed properly, because it's passed as a parameter in the try, but how should the input and output be closed properly?

Answer 1

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 statement

    try (
        java.util.zip.ZipFile zf =
             new java.util.zip.ZipFile(zipFileName);
        java.io.BufferedWriter writer = 
            java.nio.file.Files.newBufferedWriter(outputFilePath, charset)
    ) {
        // Enumerate each entry
        for (java.util.Enumeration entries =
                                zf.entries();     entries.hasMoreElements();) {
            // Get the entry name and write it to the output file
            String newLine = System.getProperty("line.separator");
            String zipEntryName =
                 ((java.util.zip.ZipEntry)entries.nextElement()).getName() 
             newLine;
            writer.write(zipEntryName, 0, zipEntryName.length());
        }
    }
}

If your objects don't implement AutoClosable (DataInputStream does), or must be declared before the try-with-resources, then the appropriate place to close them is in a finally block, also mentioned in the linked documentation.