5MB图片加载耗时8秒，如何优化BufferedInputStream的转换速度？

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bufferedinputstream转换速度优化

对于下述代码，当图片大小为5mb时，加载时间耗时8秒。如何提升其加载速度？

url url = new url(imageurl);
httpurlconnection connection = (httpurlconnection) url.openconnection();
connection.setrequestmethod("get");
connection.setconnecttimeout(5000);
bufferedinputstream bis = new bufferedinputstream(connection.getinputstream());
bytearrayoutputstream baos = new bytearrayoutputstream();
byte[] buffer = new byte[1024];
int len;
while ((len = bis.read(buffer)) != -1) {
    baos.write(buffer, 0, len);
}
outputstream outputstream = response.getoutputstream();
response.setcontenttype("image/jpg");
outputstream.write(baos.tobytearray());
outputstream.flush();
outputstream.close();

优化方案

该代码存在以下优化点：

• 内存占用高：读取数据后全部存放在内存中，当文件较大时会造成内存溢出。
• 阻塞读取：阻塞读取数据后才执行写入，造成资源浪费。
• 连接未复用：未复用http连接，增加开销。
• 资源未释放：未释放http连接和response流，造成内存泄露。

优化方案一：原始流复制

优化原始流复制，通过增大缓冲区，提高效率：

httpurlconnection connection = null;
try {
    url url = new url(imageurl);
    connection = (httpurlconnection) url.openconnection();
    connection.setrequestmethod("get");
    connection.setconnecttimeout(5000);
    try (inputstream bis = new bufferedinputstream(connection.getinputstream());
         outputstream out = response.getoutputstream()) {
        response.setcontenttype("image/jpg");
        
        // buffer 越大，效率越快
        byte[] buffer = new byte[1024];
        int len;
        while ((len = bis.read(buffer)) != -1) {
            out.write(buffer, 0, len);
            
            out.flush();
            
        }
    }
} catch (exception e) {
    throw new runtimeexception(e);
} finally {
    if(null != connection){
        connection.disconnect();
    }
}

优化方案二：使用复制工具

使用第三方库提供的方法复制流，减少代码复杂度：

httpurlconnection connection = null;
try {
    url url = new url(imageurl);
    connection = (httpurlconnection) url.openconnection();
    connection.setrequestmethod("get");
    connection.setconnecttimeout(5000);
    try (inputstream bis = new bufferedinputstream(connection.getinputstream());
         outputstream out = response.getoutputstream()) {
        response.setcontenttype("image/jpg");

        ioutil.copy(bis, out);
        
    }
} catch (exception e) {
    throw new runtimeexception(e);
} finally {
    if(null != connection){
        connection.disconnect();
    }
}

优化方案三：使用nio非阻塞传输

使用nio非阻塞传输，减少系统开销，提升效率：

HttpURLConnection connection = null;
try {
    URL url = new URL(imageUrl);
    connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("GET");
    connection.setConnectTimeout(5000);
    try (ReadableByteChannel in = Channels.newChannel(new BufferedInputStream(connection.getInputStream()));
         WritableByteChannel out = Channels.newChannel(response.getOutputStream())) {
        response.setContentType("image/jpg");

        ByteBuffer byteBuffer = ByteBuffer.allocate(8192);
        while (in.read(byteBuffer) != -1) {
            // 写转读
            byteBuffer.flip();
            out.write(byteBuffer);
            byteBuffer.clear();
        }
    }
} catch (Exception e) {
    throw new RuntimeException(e);
} finally {
    if (null != connection) {
        connection.disconnect();
    }
}

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