UF.IN

当尝试使用已被释放的资源时，就会报告 UF（使用已释放）问题。UF.IN 警告表明尝试在输入流已被关闭后使用它。

示例 1

复制 
     public boolean checkMeta(InputStream stream) {
         byte[] b = new byte[8];
         try {
             final long l = stream.available();
             if (l < 8) {
                 return false;
             }
             stream.read(b);
         } catch (IOException e) {
             return false;
         } finally {
             try {
                 stream.close();
             } catch (IOException e) {
                 // do nothing
             }
         }
 
         // Cast unsigned character constants prior to comparison
         return (b[0] == (byte) 'm' && b[1] == (byte) 'y' &&
                 b[2] == (byte) 'f' && b[3] == (byte) 'o' &&
                 b[4] == (byte) 'r' && b[5] == (byte) 'm' &&
                 b[6] == (byte) 'a' && b[7] == (byte) 't');
     }
 
     public void printOut(final URL url, final PrintStream ps) throws IOException {
         final InputStream stream = url.openStream();
         if (checkMeta(stream)) {
             try {
                 ps.println("content:");
                 byte[] b = new byte[1024];
                 int i;
                 while ((i = stream.read(b)) > 0) {
                     ps.print(new String(b, 0, i));
                 }
                 ps.println();
             } catch (IOException e) {
                 e.printStackTrace();
             }
         }
     }

针对第 50 行的代码段报告 UF.IN：在第 30 行关闭了输入流 stream 后再次使用它。

示例 2

复制 
     public boolean checkMeta(InputStream stream) {
         byte[] b = new byte[8];
         try {
             final long l = stream.available();
             if (l < 8) {
                 return false;
             }
             stream.read(b);
         } catch (IOException e) {
             return false;
         }
 
         // Cast unsigned character constants prior to comparison
         return (b[0] == (byte) 'm' && b[1] == (byte) 'y' &&
                 b[2] == (byte) 'f' && b[3] == (byte) 'o' &&
                 b[4] == (byte) 'r' && b[5] == (byte) 'm' &&
                 b[6] == (byte) 'a' && b[7] == (byte) 't');
     }
 
     public void printOut(final URL url, final PrintStream ps) throws IOException {
         final InputStream stream = url.openStream();
         try {
             if (checkMeta(stream)) {
                 try {
                     ps.println("content:");
                     byte[] b = new byte[1024];
                     int i;
                     while ((i = stream.read(b)) > 0) {
                         ps.print(new String(b, 0, i));
                     }
                     ps.println();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
         } finally {
             try {
                 stream.close();
             } catch (IOException e) {
                 // do nothing
             }
         }
     }

来自之前部分的代码段经过了修复。方法“checkMeta”不再关闭流。现在，它通过“printOut”方法来关闭，即开启该流的方法。通常，通过最初用来分配资源的相同方法来释放资源是良好的编码做法。