{"id":59767,"date":"2020-08-23T14:38:27","date_gmt":"2020-08-23T14:38:27","guid":{"rendered":"https:\/\/www.baeldung.com\/?p=86073"},"modified":"2020-08-23T14:38:27","modified_gmt":"2020-08-23T14:38:27","slug":"reading-a-line-at-a-given-line-number-from-a-file-in-java","status":"publish","type":"post","link":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/2020\/08\/23\/reading-a-line-at-a-given-line-number-from-a-file-in-java\/","title":{"rendered":"Reading a Line at a Given Line Number From a File in Java"},"content":{"rendered":"

<\/p>\n

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

In this quick article, we’re going to look at different ways of reading a line at a given line number inside a file.<\/p>\n

2. Input File<\/h2>\n
<\/div>\n

Let’s start by creating a simple file named inputLines.txt<\/em> that we’ll use in all of our examples:<\/p>\n

Line 1\r\nLine 2\r\nLine 3\r\nLine 4\r\nLine 5<\/code><\/pre>\n
3. Using BufferedReader<\/em><\/h2>\n
<\/div>\n
Let’s look at the well known BufferedReader<\/em><\/a> class and its advantage of not storing the entire file into memory.<\/p>\n
We can read a file line by line and stop when we desire:<\/strong><\/p>\n
@Test\r\npublic void givenFile_whenUsingBufferedReader_thenExtractedLineIsCorrect() {\r\n    try (BufferedReader br = Files.newBufferedReader(Paths.get(FILE_PATH))) {\r\n        for (int i = 0; i < 3; i++) {\r\n            br.readLine();\r\n        }\r\n        String extractedLine = br.readLine();\r\n        assertEquals(\"Line 4\", extractedLine);\r\n    }\r\n}<\/code><\/pre>\n
4. Using Scanner<\/em><\/h2>\n
<\/div>\n
Another similar approach we can take is using a Scanner<\/em><\/a>:<\/p>\n
@Test\r\npublic void givenFile_whenUsingScanner_thenExtractedLineIsCorrect() {\r\n    try (Scanner scanner = new Scanner(new File(FILE_PATH))) {\r\n        for (int i = 0; i < 3; i++) {\r\n            scanner.nextLine();\r\n        }\r\n        String extractedLine = scanner.nextLine();\r\n        assertEquals(\"Line 4\", extractedLine);\r\n    }\r\n}<\/code><\/pre>\n
Although on small files, the difference between BufferedReader<\/em> and Scanner\u00a0<\/em>might not be noticeable, on larger files, the Scanner<\/em> will be slower since it also does parsing<\/a> and has a smaller buffer size.<\/strong><\/p>\n
5. Using the File API<\/h2>\n
<\/div>\n
5.1. Small Files<\/h3>\n
<\/div>\n
We can use Files.readAllLines() <\/em>from the File API<\/a> to easily read the contents of a file into memory and extract the line we desire:<\/p>\n
@Test\r\npublic void givenSmallFile_whenUsingFilesAPI_thenExtractedLineIsCorrect() {\r\n    String extractedLine = Files.readAllLines(Paths.get(FILE_PATH)).get(4);\r\n    assertEquals(\"Line 5\", extractedLine);\r\n}<\/code><\/pre>\n
5.2. Large Files<\/h3>\n
<\/div>\n
If we need to work with large files, we should use the lines<\/em> method, which returns a Stream<\/em> so that we can read the file line by line:<\/strong><\/p>\n
@Test\r\npublic void givenLargeFile_whenUsingFilesAPI_thenExtractedLineIsCorrect() {\r\n    try (Stream lines = Files.lines(Paths.get(FILE_PATH))) {\r\n        String extractedLine = lines.skip(4).findFirst().get();\r\n        assertEquals(\"Line 5\", extractedLine);\r\n    }\r\n}<\/code><\/pre>\n
6. Using Apache Commons IO<\/h2>\n
<\/div>\n
Another option is using the FileUtils\u00a0<\/em>class of the commons-io<\/strong><\/a> package, which reads the whole file and returns the lines as a list of String<\/em>s:<\/p>\n
@Test\r\npublic void givenFile_whenUsingFileUtils_thenExtractedLineIsCorrect() {\r\n    ClassLoader classLoader = getClass().getClassLoader();\r\n    File file = new File(classLoader.getResource(\"linesInput.txt\").getFile());\r\n    List<String> lines = FileUtils.readLines(file, \"UTF-8\");\r\n    String extractedLine = lines.get(0);\r\n    assertEquals(\"Line 1\", extractedLine);\r\n}<\/code><\/pre>\n
We can also use the IOUtils<\/em> class to achieve the same result, except this time, the whole content is returned as a String<\/em>, and we have to do the splitting ourselves:<\/strong><\/p>\n
@Test\r\npublic void givenFile_whenUsingIOUtils_thenExtractedLineIsCorrect() {\r\n    String fileContent = IOUtils.toString(new FileInputStream(FILE_PATH), StandardCharsets.UTF_8);\r\n    String extractedLine = fileContent.split(System.lineSeparator())[0];\r\n    assertEquals(\"Line 1\", extractedLine);\r\n}<\/code><\/pre>\n
7. Conclusion<\/h2>\n
<\/div>\n
In this quick article, we’ve gone over the most common ways of reading a line at a given line number from a file.<\/p>\n
As usual, the examples are available over on GitHub<\/a>.<\/p>\n
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<\/p>","protected":false},"excerpt":{"rendered":"
Learn different ways of reading a line at a given line number inside a file<\/p>\n
<\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/div>\n<\/div>","protected":false},"author":758,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"slim_seo":{"title":"Reading a Line at a Given Line Number From a File in Java - ITTeacherITFreelance.hk","description":"Learn different ways of reading a line at a given line number inside a file                "},"footnotes":""},"categories":[6],"tags":[4787],"_links":{"self":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/59767"}],"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\/758"}],"replies":[{"embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/comments?post=59767"}],"version-history":[{"count":8,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/59767\/revisions"}],"predecessor-version":[{"id":64365,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/59767\/revisions\/64365"}],"wp:attachment":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/media?parent=59767"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/categories?post=59767"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/tags?post=59767"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}