java http下载文件。在activemq blobmessage 的blob对象读时用到。

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:

1. You're not just treating the input as bytes，未彻底二进制处理
2. You're needlessly pulling the entire object into memory at once，性能考虑
3. 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();