How to convert csv to a map using Java 8 Stream

问题

I'm trying to create a simple parsing util that converts a two-column CSV file and put it into a map.

public Map<String, String> getMapFromCSV(final String filePath) throws IOException {
    return Files.lines(Paths.get(filePath))
                .map(line -> line.split(","))
                .collect(Collectors.toMap(line -> line[0], line -> line[1]));
}

As you can see, I'm creating a stream of strings, delimiting each line on a comma and transforming it into a string array, and finally mapping key to index 0 and value to index 1.

@Test
public void testGetMapFromCSV() throws IOException{
    actual = util.getMapFromCSV(filePath).get("AL");
    expected = "ALABAMA";

    assertEquals(expected, actual);
}

For some reason, when I run this test, the actual value is null. I ruled out invalid filePath because it's working fine in another unit test, and the key value is present in the CSV. I've been staring at it for a few hours now, figured maybe someone here could point out my error.

Also, I'm fairly new to Java 8, so if anyone knows a better/cleaner way of writing this, I'd appreciate the feedback.

回答1:

Ok, I added lines.close() and removed any whitespace from the csv and it works! Strange, considering the csv got parsed fine in my other method. Here's what it looks like:

public static Map<String, String> getMapFromCSV(final String filePath) throws IOException{

        Stream<String> lines = Files.lines(Paths.get(filePath));
        Map<String, String> resultMap = 
                lines.map(line -> line.split(","))
                     .collect(Collectors.toMap(line -> line[0], line -> line[1]));

        lines.close();

        return resultMap;
    }

来源：https://stackoverflow.com/questions/36482896/how-to-convert-csv-to-a-map-using-java-8-stream