Question

考虑一下：

public static void read(String filename) throws IOException {
    String charsetName = "UTF-8";
    InputStream file = new FileInputStream(filename); // say no problem
    InputStreamReader reader = new InputStreamReader(file, charsetName);
    BufferedReader buffer = new BufferedReader(reader);
    try {
        buffer.readLine();
    } finally {
        try {
            buffer.close();
        } catch (IOException e) {
            // report at least
            e.printStackTrace();
        }
    }
}

如果new InputStreamReader(file, charsetName)抛出UnsupportedEncodingException，则永远不会调用buffer.close();行。替代方案是额外的冗长：

InputStream file = new FileInputStream(filename);
try {
    InputStreamReader reader = new InputStreamReader(file);
    try {
        BufferedReader buffer = new BufferedReader(buffer);
        try {
            buffer.readLine();
        } finally {
            buffer.close(); // should catch
        }
    } finally {
        reader.close(); // should catch
    }
} finally {
    file.close(); // should catch
}

并且它不必要地关闭所有流（而output.close();应该足够 - 实际上任何一个都应该足够成功 - see comments in the code by Skeet）。

包装构造函数

BufferedReader buffer = new BufferedReader(
              new InputStreamReader(new FileInputStream(filename), charsetName));

基本上只是隐藏了这个问题。

请注意我使用@ TomHawtin-tackline here建议的try-finally惯用语 - 但更常见的方法是：

public static void read(String filename) throws IOException {
    String charsetName = "UTF-8";
    InputStream file = null;
    InputStreamReader reader = null;
    BufferedReader buffer = null;
    try {
        file = new FileInputStream(filename);
        reader = new InputStreamReader(file, charsetName);
        buffer = new BufferedReader(reader);
        buffer.readLine();
    } finally {
        try {
            if(buffer != null) buffer.close();
        } catch (IOException e) {
            // report at least
            e.printStackTrace();
        }
        // Rinse and repeat for the rest
    }
}

很尴尬。

问题：

你如何处理这个案子？
会：

public static void read(String filename) throws IOException {
    String charsetName = "UTF-8";
    InputStream file = new FileInputStream(filename);
    try {
        InputStreamReader reader = new InputStreamReader(file, charsetName);
        BufferedReader buffer = new BufferedReader(reader); // Eclipse warning
        buffer.readLine();
        // notice that if these were out put streams we SHOULD FLUSH HERE
    } finally {
        try {
            file.close();
        } catch (IOException e) {
            // report at least
            e.printStackTrace();
        }
    }
}

吗？换句话说， 关闭最里面的流 （与usually asked相反）将是more than 2时最干净的解决方案包裹的溪流？ 是否有finally装饰器也应关闭（）的情况？例如，参见点here。请注意Eclipse警告：

资源泄漏：“缓冲区”永远不会关闭

Eclipse是对的吗？

_{这是Java 6 - Android只是Java 6我才提醒你。试图在一些实用程序类中分解IO代码，一劳永逸}

Answer 1

在上一个方法中，根据关闭流的规则，eclipse显示的Resource leak警告是正确的。关闭最里面的流只关闭该流，而不是关闭该流的其他流。但关闭最外层的流是一次性操作，它将自动关闭所有底层流。正如文章Always close streams中所述：

如果将多个流链接在一起，则关闭其中的一个是最后一个被建造的，因此处于最高水平抽象，将自动关闭所有底层流。所以，一个人只需要在一个流上调用close来关闭（并刷新，如果适用的话）整个系列的相关流。

所以我认为以下代码是您案例的解决方案：

public static void read(String filename) throws IOException {
    String charsetName = "UTF-8";
    InputStream file = null;
    InputStreamReader reader = null;
    BufferedReader buffer = null;
    try 
    {
        file = new FileInputStream(filename);                
        reader = new InputStream(file,charsetName);
        buffer = new BufferedReader(reader);
        buffer.readLine();
    } 
    finally 
    {
         closeQuietly(buffer,reader,file);
    }
}

修改
正如@jtahlborn所建议的，在finally块中编写的代码包含在实用程序方法中，如下所示：

public static void closeQuietly(Closeable... closeables) { if(closeables == null) { return; } for (Closeable c : closeables) { doCloseQuietly(c); } } public static void doCloseQuietly(Closeable c) { try { if (c != null) { c.close(); } } catch (IOException ex) { ex.printStackTrace(); } }

Answer 2

第二种模式（检查空值1）可以修改为：

public static void readSO2(String filename) throws IOException {
    String charsetName = "UTF-8";
    InputStream file = null;
    InputStreamReader reader = null;
    BufferedReader buffer = null;
    try {
        file = new FileInputStream(filename);
        reader = new InputStreamReader(file, charsetName);
        buffer = new BufferedReader(reader);
        buffer.readLine();
    } finally {
        try {
            if (buffer != null) buffer.close();
            else if (reader != null) reader.close();
            else if (file != null) file.close();
        } catch (IOException e) {
            // report at least
            e.printStackTrace();
        }
    }
}

优点：一次关闭，一次可能异常，无需刷新（输出流）
缺点：仍然不优雅：null舞蹈，必须小心ifs的顺序，没有办法概括

所以问题仍然存在。

java 6 IO - 包裹流关闭

问题：

2 个答案: