Question

我写了个下载程序，用Java写的，但是写完以后发现下载大文件的时候报错，内存溢出，能看看是哪的问题么？

我写了个下载程序，用Java写的，但是写完以后发现下载大文件的时候报错，内存溢出，能看看是哪的问题么？Exception in thread "http-bio-8080-exec-10" java.lang.OutOfMemoryError: Java heap space，要怎么优化一下才行呢？我把代码也粘到下面吧，麻烦大神们帮我看看是代码的问题么？
public class downloadServlet extends HttpServlet {

@Override
protected void service(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
String path = request.getParameter("filename");
path = new String(path.getBytes("ISO-8859-1"), "utf-8");
System.out.println("23:"+path);
download(path, request, response);
}
@SuppressWarnings("deprecation")
public HttpServletResponse download(String path,
HttpServletRequest request, HttpServletResponse response) {
try {

System.out.println(request.getRealPath("/") + "/"
+ "upload/" + path);
File file = new File(request.getRealPath("/") + "/"
+ "upload/" + path);
String filename = file.getName();
InputStream fis = new BufferedInputStream(new FileInputStream(file));
byte[] buffer = new byte[fis.available()];
fis.read(buffer);
fis.close();
response.reset();
response.addHeader("Content-Disposition", "attachment;filename="
+ new String(filename.getBytes("utf-8"), "ISO-8859-1"));
response.addHeader("Content-Length", "" + file.length());
OutputStream toClient = new BufferedOutputStream(response
.getOutputStream());
response.setContentType("application/octet-stream");
toClient.write(buffer);
toClient.flush();
toClient.close();
} catch (IOException ex) {
ex.printStackTrace();
}
return response;
}
}

Answer 1

不能一次读取完，大文件很容易内存溢出。参考下：

public static void download(String path, HttpServletResponse response) throws Exception {   
    try {   
            File file = new File(path);   
              if (file.exists()) {   
                 String filename = file.getName();   
                 InputStream fis = new BufferedInputStream(new FileInputStream( file));   
                  response.reset();   
                  response.setContentType("application/x-download");
                  response.addHeader("Content-Disposition","attachment;filename="+ new String(filename.getBytes(),"iso-8859-1"));
                  response.addHeader("Content-Length", "" + file.length());   
                 OutputStream toClient = new BufferedOutputStream(response.getOutputStream());   
                response.setContentType("application/octet-stream");   
                  byte[] buffer = new byte[1024 * 1024 * 4];   
                  int i = -1;   
                  while ((i = fis.read(buffer)) != -1) {   
                      toClient.write(buffer, 0, i);  
                     
                  }   
                  fis.close();   
                  toClient.flush();   
                  toClient.close();   
                  try {
             response.wait();
            } catch (InterruptedException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
            }  
              } else {   
                 PrintWriter out = response.getWriter();   
                 out.print("<script>");   
                 out.print("alert(\"not find the file\")");   
                 out.print("</script>");   
              }   
          } catch (IOException ex) {   
             PrintWriter out = response.getWriter();   
                 out.print("<script>");   
                 out.print("alert(\"not find the file\")");   
                 out.print("</script>");   
          }   
    
      }

追问

我仔细看了看，好像没看出哪些代码可以避免内存溢出呀，能不能再帮忙说的明白一点呢？多谢你了

追答

你的代码里面一次读取的：

byte[] buffer = new byte[fis.available()];
fis.read(buffer);

追问

哇，真的解决了，我还专门查了查这个方法，看来不靠谱啊这方法，多谢你了！

Answer 2

主要是你的Buffer开的太大了，4*1024*1024 也就是4G了。这个缓存很有点大。其实使用1024或者4096就行了。

Answer 3

你把这么大的文件都读到内存里，当然受不了了，你去网上搜搜看看怎么分块，或者内存分流读取把！