try-with-resource 关闭 io流

1.在利用IO流的时候我们都需要关闭IO流, 比如  input.close(),一般是放在 finally 里面,但是如果多个类的话情况就会很复杂.

static void copy2(String src, String dst)  {
        InputStream in = null;
        try {
            in = new FileInputStream(src);
            OutputStream out  = null;
            try {
                //在打开InputStream后在打开OutputStream
                out = new FileOutputStream(dst);
                byte[] buf = new byte[1024];
                int n;
                while ((n = in.read(buf)) >= 0) {
                    out.write(buf, 0, n);
                }
                
            } catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                if (out != null) {
                    try {
                        out.close();
                    } catch (IOException e) {
                    }
                }
            }
        } catch (FileNotFoundException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                }
            }
        }
    }

一个简单的文件拷贝工作会整的很复杂,如果在有别的io流的话就会更复杂,整个代码很难懂,而且 close()方法调用的时候也会抛出异常,所以内部也需要捕获一次异常.

2.利用 try-with-resource

    static void copy(String src, String dst) throws Exception, IOException {
        try (InputStream in = new FileInputStream(src);
             OutputStream out = new FileOutputStream(dst)){
            byte[] buf = new byte[1024];
            int n;
            while ((n = in.read(buf)) >= 0) {
                out.write(buf, 0, n);
            }
        } finally {
        }
    }

利用 try-with-resource ,我们直接在 try ( )中声明实现了AutoCloseable 的类,就可以在代码执行完以后自动执行 close()方法,整个代码也会简洁不少.

如果有多个需要关闭的类, 直接在()中声明类然后利用分号隔开就可以.