Java I / O延迟在文件系统中创建文件

Question

I have legacy code which uses BufferedWriter to create a file in the file system.

The problem is that when there is some verification error in program it creates an empty file. It should not create the file at all when there is an verification error, but the error is detected only when data is written to it (verification). PFB the example code:

//Legacy code
    File file1= new File(<path to directory>);
    BufferedWriter dBufferedWriter = new BufferedWriter(new FileWriter(file1));

//Code that can have error and this repeats in loop
    String str = "some string or null if error occurs";
    if(validate(str)){  
        dBufferedWriter.write(str);
    }

//Later at end
    dBufferedWriter.close();

Is there a way to delay creating a file when it's not needed?

Answer 1

When you create new FileWriter it creates new file if this file does not exists. If you don't need any file in case of exception, you can use try{...}finally{...} :

File file = new File(<path to directory>);
BufferedWriter dBufferedWriter = new BufferedWriter(new FileWriter(file));
try{        
    // some code where you can get exception

    String str = "some string or null if error occurs";
    dBufferedWriter.write(str);     
}finally{
    dBufferedWriter.close();
    if(file.length()==0) file.delete();
}

By the way, it is a good practice to use finally for close resource, even if you don't need to check file length.

Sure, if you can change legacy code's order, make it so, that the file will be created after verification code. In case of exception code after verification loop will not be reached:

// some code where you can get exception

Writer fileWriter = new FileWriter(new File(<path to directory>));
String str = "some string or null if error occurs";
dBufferedWriter.write(str);     
dBufferedWriter.close();

Answer 2

So the legacy code shouldn't create the file if it isn't going to be needed. So fix that.

String str = "some string or null if error occurs";
if(validate(str)){  
    File file1= new File(<path to directory>);
    BufferedWriter writer1 = new BufferedWriter(new FileWriter(file1));
    dBufferedWriter.write(str);
    dBufferedWriter.close();        
}

... assuming dBufferedWriter and writer1 are the same thing.