在Java中读取属性文件时，我应该使用try-catch还是引发自定义异常，或者两者都使用？

Question

I am reading properties from property file in the classpath of my project.

public Properties readFileFromClasspath(String fileName) throws MyException {

    Properties props = new Properties();
    InputStream inputStream = getClass().getClassLoader().getResourceAsStream(fileName);
    if (inputStream != null) {
        try {
            props.load(inputStream);
        } catch (IOException e) {
            throw new MyException("Could Not read properties from file  : [" + fileName + "].",e);
        }
    } else {

        throw new MyException("Could Not find property file  : [" + fileName + "] in the classpath.");
    }
    return mainProperties;

 }

Here MyException simply extends Exception .

Should I use try-catch or throws MyException or both ?

Answer 1

Depends. Can you load default properties if there is an exception? In that case catch the exception, load default properties and warn in a log.

If there is impossible to load application without properties, you must thrown an exception.

You have to decide whether your exceptions can be controled or not.

Answer 2

I think you are free to choose, but in both cases, you should always be as much informative as possible when throwing. In this case, I see no reason to create a custom exception. I'd throw IOException if something bad happens while reading the properties file, otherwise FileNotFoundException if the properties file is not there. If you want to read more, here is one of the many tutorials you can find about exception handling.

Answer 3

I think sometimes we over do it with the exceptions, to me your code should only verify the file exists and throw a FileNotFoundException, other than that why throw the exception that is already being thrown? You're not doing anything special in the catch.

Answer 4

Assuming you are loading application properties during startup from a fixed-name properties file I would throw an undeclared, unchecked exception:

    public void readApplicationProperties() {
        this.properties = readFileFromClasspath("application.properties");
    }

    private Properties readFileFromClasspath(String fileName) {
        Properties props = new Properties();
        InputStream inputStream = getClass().getClassLoader().getResourceAsStream(fileName);
        if (inputStream == null) {
            throw new RuntimeException("Could not find property file: [" + fileName + "] in the classpath.");
        }
        try {
            props.load(inputStream);
        } catch (IOException e) {
            throw new RuntimeException("Could not read properties from file: [" + fileName + "].", e);
        }
        return props;
    }

My reasoning is that the application cannot recover from this error so there is no point creating a custom checked exception, catching it, etc. In the end the application will have to terminate with a meaningful error message. The simplest way to do this is with an unchecked exception.