追加二进制文件的内容

huangapple
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英文:

Appending content of binary files

问题

我想将一个文件的内容追加到另一个已存在的文件中。我使用了带有追加参数的FileOutputStream以及SequenceInputStream进行普通文件复制。这两种方法对于txt文件都有效，但对于二进制文件如pdf和excel则不起作用。

如果我尝试合并两个pdf文件，总是会覆盖结果文件中的第二个输入流。是否有其他方法可以实现二进制文件的相同操作？

以下是我的代码。

  1. package org.saurav.simpletests.io;
  3. import java.io.FileInputStream;
  4. import java.io.FileNotFoundException;
  5. import java.io.FileOutputStream;
  6. import java.io.IOException;
  7. import java.io.InputStream;
  8. import java.io.OutputStream;
  9. import java.io.SequenceInputStream;
  11. public class ConcatStreams {
  13.     public static void main(String a[]) {
  15.         ConcatStreams concatStreams = new ConcatStreams();
  17.         try {
  18.             InputStream input1 = new FileInputStream("<path to first binary file>");
  19.             InputStream input2 = new FileInputStream("<path to second binary file>");
  21.             OutputStream output = new FileOutputStream("<path to first binary file> ", true);
  22.             //concatStreams.mergeUsingSequenctInputStream(input1,input2); // uncomment it to run the code with sequenceInputStream
  23.             concatStreams.mergeUsingFileOutputAppend(output, input2);
  24.         } catch (FileNotFoundException e) {
  25.             // TODO Auto-generated catch block
  26.             e.printStackTrace();
  27.         }
  29.     }
  31.     private void mergeUsingFileOutputAppend(OutputStream outStream, InputStream input) {
  33.         try {
  34.             byte[] buffer = new byte[256];
  35.             int data;
  37.             data = input.read(buffer);
  38.             while (data != -1) {
  39.                 String str = new String(buffer, "UTF-8");
  40.                 //System.out.println(str);
  41.                 outStream.write(buffer);
  42.                 data = input.read(buffer);
  44.             }
  46.             //output.write(data);
  47.         } catch (IOException e) {
  48.             // TODO Auto-generated catch block
  49.             e.printStackTrace();
  50.         } finally {
  51.             try {
  52.                 outStream.close();
  53.             } catch (IOException e) {
  54.                 // TODO Auto-generated catch block
  55.                 e.printStackTrace();
  56.             }
  57.         }
  58.     }
  60.     private void mergeUsingSequenctInputStream(InputStream input1, InputStream input2) {
  62.         SequenceInputStream sequenceInputStream =
  63.                 new SequenceInputStream(input1, input2);
  64.         FileOutputStream fos = null;
  65.         try {
  66.             fos = new FileOutputStream("<path to first binary file>");
  67.             byte[] buffer = new byte[256];
  68.             int data;
  70.             data = sequenceInputStream.read(buffer);
  71.             while (data != -1) {
  72.                 String str = new String(buffer, "UTF-8");
  73.                 //System.out.println(str);
  74.                 fos.write(buffer);
  75.                 data = sequenceInputStream.read(buffer);
  77.             }
  78.         } catch (IOException e) {
  79.             // TODO Auto-generated catch block
  80.             e.printStackTrace();
  81.         } finally {
  82.             try {
  83.                 fos.close();
  84.             } catch (IOException e) {
  85.                 // TODO Auto-generated catch block
  86.                 e.printStackTrace();
  87.             }
  88.         }
  90.     }
  92. }

最好的问候，
Saurav

英文:

I want to append the content of one file to another existing file with content. I used plain file copy with FileOutputStream with append parameter and also with SequenceInputStream. Both are working for txt files but not for binary files like pdf and excel.

If i try to merge two pdf files always the second input stream is overwritten in the resultant file. Is there any other way i can achieve the same for binary files ?

Below is my code.

  1. package org.saurav.simpletests.io;
  2. import java.io.FileInputStream;
  3. import java.io.FileNotFoundException;
  4. import java.io.FileOutputStream;
  5. import java.io.IOException;
  6. import java.io.InputStream;
  7. import java.io.OutputStream;
  8. import java.io.SequenceInputStream;
  9. public class ConcatStreams {
  10. public static void main (String a[]) {
  11. ConcatStreams concatStreams = new ConcatStreams();
  12. try {
  13. InputStream  input1 = new FileInputStream(&quot;&lt;path to first binary file&gt;&quot;);
  14. InputStream input2 = new FileInputStream(&quot;&lt;path to second binary file&gt;&quot;);
  15. OutputStream  output = new FileOutputStream(&quot;&lt;path to first binary file&gt; &quot;,true);
  16. //concatStreams.mergeUsingSequenctInputStream(input1,input2); // uncomment it to run the code with sequenceInputStream
  17. concatStreams.mergeUsingFileOutputAppend(output, input2);
  18. } catch (FileNotFoundException e) {
  19. // TODO Auto-generated catch block
  20. e.printStackTrace();
  21. }
  22. }
  23. private void mergeUsingFileOutputAppend(OutputStream outStream, InputStream input) {
  24. try {
  25. byte[] buffer = new byte[256];
  26. int data;
  27. data = input.read(buffer);
  28. while(data != -1){
  29. String str = new String(buffer, &quot;UTF-8&quot;);
  30. //System.out.println(str);
  31. outStream.write(buffer);
  32. data = input.read(buffer);
  33. }
  34. //output.write(data);
  35. } catch (IOException e) {
  36. // TODO Auto-generated catch block
  37. e.printStackTrace();
  38. } finally {
  39. try {
  40. outStream.close();
  41. } catch (IOException e) {
  42. // TODO Auto-generated catch block
  43. e.printStackTrace();
  44. }
  45. }
  46. }
  47. private void mergeUsingSequenctInputStream(InputStream input1, InputStream input2) {
  48. SequenceInputStream sequenceInputStream =
  49. new SequenceInputStream(input1, input2);
  50. FileOutputStream fos = null;
  51. try {
  52. fos = new FileOutputStream(&quot;&lt;path to first binary file&gt;&quot;);
  53. byte[] buffer = new byte[256];
  54. int data;
  55. data = sequenceInputStream.read(buffer);
  56. while(data != -1){
  57. String str = new String(buffer, &quot;UTF-8&quot;);
  58. //System.out.println(str);
  59. fos.write(buffer);
  60. data = sequenceInputStream.read(buffer);
  61. }
  62. } catch (IOException e) {
  63. // TODO Auto-generated catch block
  64. e.printStackTrace();
  65. } finally {
  66. try {
  67. fos.close();
  68. } catch (IOException e) {
  69. // TODO Auto-generated catch block
  70. e.printStackTrace();
  71. }
  72. }
  73. }
  74. }

Best Regards,
Saurav

答案1

得分: 1

你的实现中有一个bug：你总是将固定大小的字节块（等于缓冲区大小）写入输出流，请注意这行代码：

  1. outStream.write(buffer);

请考虑到输入流可能存在小于缓冲区大小的余数。
修复应该使用以下行：

  1. outStream.write(buffer, 0, data);

我已经像这样更新了你的代码，并成功合并了一个分为两部分的JPEG文件。

英文:

There is a bug in your implementation: you always write fixed chunks of bytes (equal to the size of buffer) to output stream, please take attention to this line:

  1. outStream.write(buffer);

Please take into account that input stream might have a remainder that is less than buffer size.
The fix should be using the following line:

  1. outStream.write(buffer, 0, data);

I've updated your code like this and was able to join jpeg file that was split into 2 parts.

huangapple
  • 本文由 发表于 2020年7月22日 01:36:31
  • 转载请务必保留本文链接：https://go.coder-hub.com/63020017.html
  • java
  • java-io
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