使用 try-with-resources 或在“finally”子句中关闭此“BufferedReader”

Question

一直在寻找解决此问题的方法。阅读所有以前的答案，但没有一个帮助我。 SonarQube 会不会有什么错误？

public class Br {

    public String loader(String FilePath){

        BufferedReader br;
        String str = null;
        StringBuilder strb = new StringBuilder();
        try {
            br = new BufferedReader(new FileReader(FilePath));
            while ((str = br.readLine()) != null) {
                strb.append(str).append("\n");
            }
        } catch (FileNotFoundException f){
            System.out.println(FilePath+" does not exist");
            return null;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return strb.toString();
    }
}

Answer 1

您没有调用br.close()，这意味着冒着资源泄漏的风险。为了可靠地关闭BufferedReader，您有两种选择：

使用finally 块：

public String loader(String FilePath) {
    // initialize the reader with null
    BufferedReader br = null;
    String str = null;
    StringBuilder strb = new StringBuilder();

    try {
        // really initialize it inside the try block
        br = new BufferedReader(new FileReader(FilePath));
        while ((str = br.readLine()) != null) {
            strb.append(str).append("\n");
        }
    } catch (FileNotFoundException f) {
        System.out.println(FilePath + " does not exist");
        return null;
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        // this block will be executed in every case, success or caught exception
        if (br != null) {
            // again, a resource is involved, so try-catch another time
            try {
                br.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    return strb.toString();
}

使用try-with-resources 声明：

public String loader(String FilePath) {
    String str = null;
    StringBuilder strb = new StringBuilder();

    // the following line means the try block takes care of closing the resource
    try (BufferedReader br = new BufferedReader(new FileReader(FilePath))) {
        while ((str = br.readLine()) != null) {
            strb.append(str).append("\n");
        }
    } catch (FileNotFoundException f) {
        System.out.println(FilePath + " does not exist");
        return null;
    } catch (IOException e) {
        e.printStackTrace();
    }

    return strb.toString();
}

Answer 2

似乎您只想读取文件中的所有行。你可以使用这个：

public String loader(String FilePath) {
    try(Scanner s = new Scanner(new File(FilePath).useDelimiter("\\A")) {
        return s.hasNext() ? s.next() : null;
    } catch(IOException e) {
        throw new UncheckedIOException(e);
    }
}

Answer 3

您编写的代码确实在泄漏资源，因为您没有关闭 BufferedReader。以下 sn-p 应该可以解决问题：

public String loader(String filePath){
    String str = null;
    StringBuilder strb = new StringBuilder();
    // try-with-resources construct here which will automatically handle the close for you
    try (FileReader fileReader = new FileReader(filePath); 
         BufferedReader br = new BufferedReader(fileReader);){
        while ((str = br.readLine()) != null) {
            strb.append(str).append("\n");
        }
    }
    catch (FileNotFoundException f){
        System.out.println(filePath+" does not exist");
        return null;
    }
    catch (IOException e) {
        e.printStackTrace();
    }
    return strb.toString();
}

如果您对此代码仍有问题，那么是的，这是 SonarQubes 的错误 :-)