When I was working on a project yesterday, I used the knowledge of downloading files from the server and saving them locally. I have never touched it before. I worked on it for a day yesterday, and this small function was realized. The following is a brief description of the realization process;
1. Basic knowledge
When we want to download a resource on the website, we will get a url, which is a description of the resource located by the server. The download process has the following steps:
(1) The client initiates a url request to obtain the connection object.
(2) The server parses the url and returns the specified resource as an input stream to the client.
(3) Create a storage directory and a saved file name.
(4) Write data is output.
(5) Close the input stream and output stream.
2. How to implement the code
/**
* @Function to download temporary material interface
* @param filePath The directory where the file will be saved
* @param method request method, including POST and GET
* @param url the requested path
* @return
*/
public static File saveUrlAs(String url,String filePath,String method){
//System.out.println("fileName---->"+filePath);
//Create a different folder directory
File file=new File(filePath);
//Check if the folder exists
if (!file.exists())
{
//If the folder does not exist, create a new folder
file.mkdirs();
}
FileOutputStream fileOut = null;
HttpURLConnection conn = null;
InputStream inputStream = null;
try
{
// create link
URL httpUrl=new URL(url);
conn=(HttpURLConnection) httpUrl.openConnection();
//Submit the form in Post mode, default get mode
conn.setRequestMethod(method);
conn.setDoInput(true);
conn.setDoOutput(true);
// post method cannot use cache
conn.setUseCaches(false);
//connect to the specified resource
conn.connect();
//get network input stream
inputStream=conn.getInputStream();
BufferedInputStream bis = new BufferedInputStream(inputStream);
/ / Determine whether the save path of the file ends with /
if (!filePath.endsWith("/")) {
filePath += "/";
}
//Write to the file (note that the file save path must be followed by the name of the file)
fileOut = new FileOutputStream(filePath+"123.png");
BufferedOutputStream bos = new BufferedOutputStream(fileOut);
byte[] buf = new byte[4096];
int length = bis.read(buf);
//save document
while(length != -1)
{
bos.write(buf, 0, length);
length = bis.read(buf);
}
bos.close();
bis.close();
conn.disconnect();
} catch (Exception e)
{
e.printStackTrace ();
System.out.println("Throw exception!!");
}
return file;
}
3. Code test class (main function)
/**
* @param args
*/
public static void main(String[] args)
{
String photoUrl = "https://ss0.bdstatic.com/5aV1bjqh_Q23odCf/static/superman/img/logo/bd_logo1_31bdc765.png";
String fileName = photoUrl.substring(photoUrl.lastIndexOf("/"));
//System.out.println("fileName---->"+fileName);
String filePath = "d:";
File file = saveUrlAs(photoUrl, filePath + fileName,"GET");
System.out.println("Run ok!/n<BR>Get URL file " + file);
}