Java：讀取文本文件時，如何讀取包含特定字符串的特定行？

Question

        try(BufferedReader br = new BufferedReader(new FileReader("MANIFEST.MF"))) {
        StringBuilder sb = new StringBuilder();
        String line = br.readLine();

        while (line != null) {
            sb.append(line);
            sb.append(System.lineSeparator());
            line = br.readLine();
        }
        String everything = sb.toString();
        System.out.println(everything);

這就是我用來讀取文件中所有文本的方式，我很好奇如何更改此順序以使我讀取包含例如“ Main-Class”的特定行。

提前致謝！

Answer 1

檢查行變量是否包含要查找的字符串，然后退出while循環...或對該行執行任何操作。 您可能還想將代碼更改為此...更加簡潔和易讀。

String line = null;

    while ((line = br.readLine()) != null) {
        sb.append(line);
        sb.append(System.lineSeparator());
    }

Answer 2

要查找包含“ Main-Class”的第一行：

try ( BufferedReader reader = new BufferedReader( new FileReader("MANIFEST.MF")) ) {

  String line = null;
  while ( ( line = reader.readLine() ) != null ) {
    if ( line.contains("Main-Class") ) break;
  }

  if ( line != null ) {
    // line was found
  } else {
    // line was not found
  }
}

查找包含“ Main-Class”的所有行：

StringBuilder matchedLines = new StringBuilder();
try ( BufferedReader reader = new BufferedReader( new FileReader("MANIFEST.MF")) ) {

  String line = null;
  while ( ( line = reader.readLine() ) != null ) {
    if ( line.contains("Main-Class") ) {
      matchedLines.append(line);
      matchedLines.append(System.lineSeparator());
    }
  }
}
// ...
System.out.println("Matched Lines:");
System.out.println(matchedLines.toString());