在文本文件中查找字符串的方法.然后将以下行达到一定限度

Question

所以这就是我到目前为止所做的:

public String[] findStudentInfo(String studentNumber) {
                Student student = new Student();
                Scanner scanner = new Scanner("Student.txt");
                // Find the line that contains student Id
                // If not found keep on going through the file
                // If it finds it stop
                // Call parseStudentInfoFromLine get the number of courses
                // Create an array (lines) of size of the number of courses plus one
                // assign the line that the student Id was found to the first index value of the array
                //assign each next line to the following index of the array up to the amount of classes - 1
                // return string array
}

我知道如何找到一个文件是否包含我想要找到的字符串,但我不知道如何检索它所在的整行.

这是我第一次发帖所以如果我做错了请告诉我.

Answer 1

你可以这样做:

File file = new File("Student.txt");

try {
    Scanner scanner = new Scanner(file);

    //now read the file line by line...
    int lineNum = 0;
    while (scanner.hasNextLine()) {
        String line = scanner.nextLine();
        lineNum++;
        if(<some condition is met for the line>) { 
            System.out.println("ho hum, i found it on line " +lineNum);
        }
    }
} catch(FileNotFoundException e) { 
    //handle this
}

Answer 2

使用Apache Commons IO API https://commons.apache.org/proper/commons-io/我能够使用它来建立这个FileUtils.readFileToString(file).contains(stringToFind)

该功能的文档位于https://commons.apache.org/proper/commons-io/javadocs/api-2.4/org/apache/commons/io/FileUtils.html#readFileToString(java.io.File)

Answer 3

当你阅读文件时，你是否考虑过逐行阅读？这将允许您检查您的行是否包含您正在读取的文件，然后您可以基于此执行您需要的任何逻辑？

Scanner scanner = new Scanner("Student.txt");
String currentLine;

while((currentLine = scanner.readLine()) != null)
{
    if(currentLine.indexOf("Your String"))
    {
         //Perform logic
    }
}

您可以使用变量来保存行号，也可以使用布尔值来指示是否已传递包含字符串的行：

Scanner scanner = new Scanner("Student.txt");
String currentLine;
int lineNumber = 0;
Boolean passedLine = false;
while((currentLine = scanner.readLine()) != null)
{
    if(currentLine.indexOf("Your String"))
    {
         //Do task
         passedLine = true;
    }
    if(passedLine)
    {
       //Do other task after passing the line.
    }
    lineNumber++;
}

Answer 4

这是在文本文件中查找字符串的 java 8 方法：

for (String toFindUrl : urlsToTest) {
        streamService(toFindUrl);
    }

private void streamService(String item) {
        try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
           stream.filter(lines -> lines.contains(item))
                       .forEach(System.out::println);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }