如何使用PrintWriter克服内存不足异常？

Question

The following code reads a bunch of .csv files and then combines them into one .csv file. I tried to system.out.println ... all datapoints are correct, however when i try to use the PrintWriter I get:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space .

I tried to use FileWriter but got the same error. How should I correct my code?

public class CombineCsv {
    public static void main(String[] args) throws IOException {
        PrintWriter output  = new PrintWriter("C:\\User\\result.csv");
        final File file = new File("C:\\Users\\is");
        int i = 0;
        for (final File child: file.listFiles()) {
            BufferedReader CSVFile = new BufferedReader( new FileReader( "C:\\Users\\is\\"+child.getName()));
            String dataRow = CSVFile.readLine(); 
            while (dataRow != null) {
                String[] dataArray = dataRow.split(",");
                for (String item:dataArray) { 
                    System.out.println(item + "\t");
                    output.append(item+","+child.getName().replaceAll(".csv", "")+",");
                    i++;
                }
                dataRow = CSVFile.readLine(); // Read next line of data.
            } // Close the file once all data has been read.
            CSVFile.close();
        } 
        output.close();
        System.out.println(i);
    } 
}

Answer 1

I can only think of two scenarios in which that code could result in an OOME:

• If the file directory has a very large number of elements, then file.listFiles() could create a very large array of File objects.

• If one of the input files includes a line that is very long, then CSVFile.readLine() could use a lot of memory in the process of reading it. (Up to 6 times the number of bytes in the line.)

The simplest approach to solving both of these issues is to increase the Java heap size using the -Xmx JVM option.

---

I can see no reason why your use of a PrintWriter would be the cause of the problem.

Answer 2

Try

boolean autoFlush = true; PrintWriter output = new PrintWriter(myFileName, autoFlush);

It creates a PrintWriter instance which flushes content everytime when there is a new line or format.