8

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.

ROMANIA_engineer
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ark234
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    You are leaking a file descriptor here. `Files.lines()` should be opened in a try-with-resources statement. – fge Apr 07 '16 at 17:13
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    Is there whitespace in the file? – rgettman Apr 07 '16 at 17:14
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    `null` may suggests that `map.get(key)` couldn't find `key` in map. Try printing entire map returned by `util.getMapFromCSV(filePath)`. – Pshemo Apr 07 '16 at 17:15
  • @fge doesn't collect() close the stream? – ark234 Apr 07 '16 at 17:18
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    No it doesn't. It consumes all the elements but doesn't call `.close()`. You have to do it yourself. (by the way, it is `BaseStream` which implements `AutoCloseable`, and `Stream` extends `BaseStream`) – fge Apr 07 '16 at 17:34
  • You might try filtering out empty lines before the split – Hank D Apr 07 '16 at 20:08

3 Answers3

9

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;
    }
ark234
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2

Try-with-resources with AutoCloseable

As commented by fge, using try-with-resources makes this easier.

Here is the code from your Answer but using try-with-resources to automatically close a Stream that is also AutoCloseable. And some added SPACE characters for breathing room.

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

    try (
        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] )
                     );
        return resultMap;
    }
    // The `Stream` named `lines` is automatically closed at this point by the try-with-resources.
}

When the {…} block of the try-with-resources ends, any resources opened in the try are automatically closed, in reverse order of their opening. This is true whether flow-of-control leaves the block gracefully upon completion, or abruptly due to an exception or a return (as seen in your code). See discussion on this Question, Try-with-resources and return statements in java.

Basil Bourque
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0

in a form that might be easier to read – with mapping

public static Map<String, String> getMapFromCSV(final String filePath) throws IOException {
  try(Stream<String> lines = Files.lines(Paths.get(filePath))) {
      return lines.collect(
        mapping(s -> s.split(","), toMap(k -> k[0], v -> v[1])));
  }
}
Kaplan
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