如何使用Java 8 Stream将csv转换为地图 [英] How to convert csv to a map using Java 8 Stream

问题描述

我正在尝试创建一个简单的解析工具，它可以转换两列CSV文件并将其放入地图中。

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]));
}

正如你所看到的，我正在创建一个字符串流，分隔每个字符串在逗号上行，并将其转换为字符串数组，最后将键映射到索引0，将值映射到索引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);
}

出于某种原因，当我运行此测试时，实际值为null。我排除了无效的filePath，因为它在另一个单元测试中工作正常，并且键值存在于CSV中。我一直在盯着它看几个小时，想想也许这里有人可以指出我的错误。

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.

另外，我对Java 8还不熟悉，所以如果有人知道更好/更清晰的写作方式，我会很感激反馈。

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

推荐答案

好的，我添加了 lines.close（）并从csv中删除了任何空格它的工作原理！奇怪的是，考虑到csv在我的其他方法中被解析得很好。这是它的样子：

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;
    }

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