java - How to avoid throwing exception from finally block

Question

I don't want toJson to throw an Exception, but the finally block might throw it. Would it be preferable to wrap the bas.close() in a try/catch block or should this be re-written using try-with-resources

public String toJson() {
    String json = null;
    ByteArrayOutputStream bas = null;

    try {
        bas = new ByteArrayOutputStream();
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.writeValue(bas, this);

        json = new String(bas.toByteArray());
    } catch (Exception e) {
        log.trace("Unable to parse JSON", e); 
    } finally {
        if (bas != null) {
            bas.close();
        }   
    }   

    return json;
}   

question from:https://stackoverflow.com/questions/65917108/how-to-avoid-throwing-exception-from-finally-block

Answer 1

You should do it using the try-with-resources statement. Given below is an excerpt from the Oracle's tutorial on The try-with-resources Statement which clearly states the benefit of using it:

Prior to Java SE 7, you can use a finally block to ensure that a resource is closed regardless of whether the try statement completes normally or abruptly. The following example uses a finally block instead of a try-with-resources statement:

static String readFirstLineFromFileWithFinallyBlock(String path)
                                                     throws IOException {
    BufferedReader br = new BufferedReader(new FileReader(path));
    try {
        return br.readLine();
    } finally {
        if (br != null) br.close();
    }
}

However, in this example, if the methods readLine and close both throw exceptions, then the method readFirstLineFromFileWithFinallyBlock throws the exception thrown from the finally block; the exception thrown from the try block is suppressed. In contrast, in the example readFirstLineFromFile, if exceptions are thrown from both the try block and the try-with-resources statement, then the method readFirstLineFromFile throws the exception thrown from the try block; the exception thrown from the try-with-resources block is suppressed. In Java SE 7 and later, you can retrieve suppressed exceptions; see the section Suppressed Exceptions for more information.

Using the try-with-resources statement, you can write your method as follows:

public String toJson() throws Exception {
    String json = null;

    try (ByteArrayOutputStream bas = new ByteArrayOutputStream()) {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.writeValue(bas, this);

        json = new String(bas.toByteArray());
    } 
    return json;
}