java http下载文件。在activemq blobmessage 的blob对象读时用到。-优快云博客

本文链接：https://blog.youkuaiyun.com/thanq/article/details/83645752

本文针对使用Java进行文件下载过程中出现的问题，提供了有效的解决方案。主要介绍了如何正确地以二进制方式处理输入流，避免一次性将整个对象加载到内存中，并优化了读写操作以提高性能。

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http://stackoverflow.com/questions/401748/corrupt-file-when-using-java-to-download-file

错误代码

URL targetUrl = new URL(urlForFile);
InputStream content = (InputStream)targetUrl.getContent();
BufferedInputStream buffered = new BufferedInputStream(content);
File savedFile = File.createTempFile("temp",".dat");

FileOutputStream fos = new FileOutputStream(savedFile);
int letter;
while((letter = buffered.read()) != -1)
fos.write(letter);
fos.close();

三大问题:

You're not just treating the input as bytes，未彻底二进制处理
You're needlessly pulling the entire object into memory at once，性能考虑
You're doing multiple method calls for every single byte read and written -- use the array based read/write!，性能考虑

Here's a redo，经过验证的正确处理图片的代码。:

URL targetUrl = new URL(urlForFile); 
InputStream is = targetUrl.getInputStream(); 
File savedFile = File.createTempFile("temp",".dat"); 
FileOutputStream fos = new FileOutputStream(savedFile); 
 
int count; 
byte[] buff = new byte[16 * 1024]; 
while((count = is.read(buff)) != -1) { 
    fos.write(buff, 0, count); 
} 
fos.close(); 
content.close();