{"id":329559,"date":"2024-05-27T07:54:34","date_gmt":"2024-05-27T07:54:34","guid":{"rendered":"https:\/\/www.baeldung.com\/reading-csv-headers-into-a-list"},"modified":"2024-05-27T07:54:34","modified_gmt":"2024-05-27T07:54:34","slug":"reading-csv-headers-into-a-list","status":"publish","type":"post","link":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/2024\/05\/27\/reading-csv-headers-into-a-list\/","title":{"rendered":"Reading CSV Headers Into a List"},"content":{"rendered":"

<\/p>\n

\"\"<\/p>\n

1. Overview<\/h2>\n
<\/div>\n

In this short tutorial, we’ll explore different ways of reading CSV<\/a> headers into a list in Java.<\/p>\n

First, we’ll learn how to do this using JDK classes. Then, we’ll see how to achieve the same objective using external libraries such as OpenCSV<\/a> and Apache Commons CSV<\/a>.<\/p>\n

2. Using BufferedReader<\/em><\/h2>\n
<\/div>\n

The BufferedReader<\/em><\/a> class provides the easiest solution to tackle our challenge. It offers a fast and efficient way to read a CSV file as it reduces the number of IO operations by reading the content chunk by chunk<\/strong>.<\/p>\n

So, let’s see it in action:<\/p>\n

class CsvHeadersAsListUnitTest {\r\n    private static final String CSV_FILE = "src\/test\/resources\/employees.csv";\r\n    private static final String COMMA_DELIMITER = ",";\r\n    private static final List<String> EXPECTED_HEADERS = List.of("ID", "First name", "Last name", "Salary");\r\n    @Test\r\n    void givenCsvFile_whenUsingBufferedReader_thenGetHeadersAsList() throws IOException {\r\n        try (BufferedReader reader = new BufferedReader(new FileReader(CSV_FILE))) {\r\n            String csvHeadersLine = reader.readLine();\r\n            List<String> headers = Arrays.asList(csvHeadersLine.split(COMMA_DELIMITER));\r\n            assertThat(headers).containsExactlyElementsOf(EXPECTED_HEADERS);\r\n        }\r\n    }\r\n}<\/code><\/pre>\n
As we can see, we use\u00a0try-<\/a>with<\/a>-resources<\/a> to create a BufferedReader<\/em> instance. That way, we make sure that the file is closed afterward. Furthermore, we invoke the readLine()<\/em><\/a> method once to extract the first line which denotes the headers<\/strong>. Finally, we use the split()<\/em><\/a> method alongside Arrays#asList<\/em><\/a> to get the headers as a list.<\/p>\n
3. Using Scanner<\/em><\/h2>\n
<\/div>\n
The Scanner<\/em><\/a> class provides another solution to achieve the same outcome. As the name implies, it scans and reads the content of a given file<\/strong>. So, let’s add another test case to see how to use Scanner<\/em> to read CSV file headers:<\/p>\n
@Test\r\nvoid givenCsvFile_whenUsingScanner_thenGetHeadersAsList() throws IOException {\r\n    try(Scanner scanner = new Scanner(new File(CSV_FILE))) {\r\n        String csvHeadersLine = scanner.nextLine();\r\n        List<String> headers = Arrays.asList(csvHeadersLine.split(COMMA_DELIMITER));\r\n        assertThat(headers).containsExactlyElementsOf(EXPECTED_HEADERS);\r\n    }\r\n}<\/code><\/pre>\n
Similarly, the Scanner<\/em> class has the nextLine()<\/em><\/a> method that we can use to get the first line of the input file. Here, the first line represents the headers of our CSV file.<\/p>\n
4. Using OpenCSV<\/h2>\n
<\/div>\n
Alternatively, we can use the OpenCSV library to read the headers of a particular CSV file. Before getting into the nitty-gritty, let’s add its Maven dependency<\/a> to the pom.xml<\/em> file:<\/p>\n
<dependency>\r\n    <groupId>com.opencsv<\/groupId>\r\n    <artifactId>opencsv<\/artifactId>\r\n    <version>5.9<\/version>\r\n<\/dependency><\/code><\/pre>\n
Typically, OpenCSV comes with a set of ready-to-use classes and methods for reading and parsing CSV files<\/strong>. So, let’s exemplify the use of this library with a practical example:<\/p>\n
@Test\r\nvoid givenCsvFile_whenUsingOpenCSV_thenGetHeadersAsList() throws CsvValidationException, IOException {\r\n    try (CSVReader csvReader = new CSVReader(new FileReader(CSV_FILE))) {\r\n        List<String> headers = Arrays.asList(csvReader.readNext());\r\n        assertThat(headers).containsExactlyElementsOf(EXPECTED_HEADERS);\r\n    }\r\n}<\/code><\/pre>\n
As we see above, OpenCSV offers the class CSVReader<\/em> to read a given file’s content. The CSVReader<\/em> class provides the readNext()<\/em> method to retrieve the next first line directly as a String<\/em> array<\/strong>.<\/p>\n
5. Using Apache Commons CSV<\/h2>\n
<\/div>\n
Another solution is to use the Apache Commons CSV library. As the name suggests, it offers several handy features for creating and reading CSV files.<\/p>\n
To start, we need to add the latest version of its dependency<\/a> to pom.xml<\/em>:<\/p>\n
<dependency>\r\n    <groupId>org.apache.commons<\/groupId>\r\n    <artifactId>commons-csv<\/artifactId>\r\n    <version>1.11.0<\/version>\r\n<\/dependency>\r\n<\/code><\/pre>\n
In short, the CSVParser<\/em> class of Apache Commons CSV provides the getHeaderNames()<\/em> method to return a read-only list of header names<\/strong>:<\/p>\n
@Test\r\nvoid givenCsvFile_whenUsingApacheCommonsCsv_thenGetHeadersAsList() throws IOException {\r\n    CSVFormat csvFormat = CSVFormat.DEFAULT.builder()\r\n      .setDelimiter(COMMA_DELIMITER)\r\n      .setHeader()\r\n      .build();\r\n    try (BufferedReader reader = new BufferedReader(new FileReader(CSV_FILE));\r\n        CSVParser parser = CSVParser.parse(reader, csvFormat)) {\r\n        List<String> headers = parser.getHeaderNames();\r\n        assertThat(headers).containsExactlyElementsOf(EXPECTED_HEADERS);\r\n    }\r\n}<\/code><\/pre>\n
Here, we use the CSVParser<\/em> class to parse the input file according to the format specified. The headers are parsed automatically from the input file with the help of the setHeader()<\/em><\/a> method<\/strong>.<\/p>\n
6. Conclusion<\/h2>\n
<\/div>\n
In this short article, we explored different solutions for reading CSV file’s headers as a list.<\/p>\n
First, we learned how to do this using JDK. Then, we saw how to achieve the same objective using external libraries.<\/p>\n
As always, the code used in this article can be found over on GitHub<\/a>.<\/p>\n
\"\"<\/p>\n
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<\/p>","protected":false},"excerpt":{"rendered":"
\"\"<\/p>\n
Learn how to read CSV headers into a list in Java using JDK classes, OpenCSV, and Apache Commons CSV. Explore these efficient methods with code examples for each approach.<\/p>\n
<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/a>\u00a0<\/div>\n<\/div>","protected":false},"author":792,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"slim_seo":{"title":"Reading CSV Headers Into a List - ITTeacherITFreelance.hk","description":"Learn how to read CSV headers into a list in Java using JDK classes, OpenCSV, and Apache Commons CSV. Explore these efficient methods with code examples for eac"},"footnotes":""},"categories":[6,1307],"tags":[10801,10802],"_links":{"self":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/329559"}],"collection":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/users\/792"}],"replies":[{"embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/comments?post=329559"}],"version-history":[{"count":1,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/329559\/revisions"}],"predecessor-version":[{"id":329560,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/329559\/revisions\/329560"}],"wp:attachment":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/media?parent=329559"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/categories?post=329559"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/tags?post=329559"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}