后端直接从文件URL下载文件
问题描述：
需要直接在后端根据文件url下载文件
解决方案：
可根据实际情况改代码：
public AidingStudentsImportExcelRespVO excelResolver(String url, Long aidingStudentsManageId){
//创建temp.xlsx
String path = this.getClass().getResource("").getPath();//注意getResource("")里面是空字符串
String path1=path+"importexcel";
try {
File dir = new File(path1);
if(!dir.exists()){
dir.mkdirs();//创建目录
}
File f = new File(path1,"temp.xlsx");
f.deleteOnExit();
if(!f.exists()){
f.createNewFile();
}
} catch (Exception e) {
e.printStackTrace();
}
//从url读取出文件到已创建的文件中
URL website = null;
ReadableByteChannel rbc = null;
FileOutputStream fos = null;
try {
website = new URL(url);
rbc = Channels.newChannel(website.openStream());
fos = new FileOutputStream(path1+"/temp.xlsx");//本地要存储的文件地址 例如：test.txt
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
} catch (Exception e) {
e.printStackTrace();
}finally{
if(fos!=null){
try {
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(rbc!=null){
try {
rbc.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//导入名单
File file = new File(path1+"/temp.xlsx");
AidingStudentsImportExcelRespVO aidingStudentsImportExcelRespVO=null;
try {
MultipartFile cMultiFile = new MockMultipartFile("file", file.getName(), null, new FileInputStream(file));
List<AidingStudentsImportExcelVO> list = ExcelUtils.read(cMultiFile, AidingStudentsImportExcelVO.class);
aidingStudentsImportExcelRespVO = aidingStudentsImportListService.aidingStudentsImportExcelListFromCloud(aidingStudentsManageId, list);
} catch (IOException e) {
throw exception(AIDING_STUDENTS_IMPORT_LIST_FILE_IMPORT_ERROR);
}
// 删除excel文件
file.deleteOnExit();
// 返回
return aidingStudentsImportExcelRespVO;
}
关键部分（NIO）：
}
//从url读取出文件到已创建的文件中
URL website = null;
ReadableByteChannel rbc = null;
FileOutputStream fos = null;
try {
website = new URL(url);
rbc = Channels.newChannel(website.openStream());
fos = new FileOutputStream(path1+"/temp.xlsx");//本地要存储的文件地址 例如：test.txt
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
} catch (Exception e) {
e.printStackTrace();
}finally{
if(fos!=null){
try {
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(rbc!=null){
try {
rbc.close();
} catch (IOException e) {
e.printStackTrace();
另一种简单方法（IO）：
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
/**
*从网络下载资源到本地
*步骤：1 定义URL，创建URL对象
2 打开URL对应的输入管道
3 使用输入管道读取URL的数据，使用内存流(ByteArrayOutputStream)接收URL的数据
4 网络URL的数据最终变成 byte[]
5 将内存流的数据写入到本地磁盘
*/
public class DownResource {
public static void main(String[] args) {
//1定义url
String urlPath = "http://172.16.59.99:9000/fdy-data/621b3868410512079f5501608a613466fb99c438b3e1583192a852c5b5e8f2b5.xlsx";
try {
//2创建URL对象
URL url = new URL(urlPath);
//打开URL对应的输入管道
try(InputStream in = url.openStream();
//内存流用来存储URL的数据
ByteArrayOutputStream out = new ByteArrayOutputStream();
//带有缓冲区的磁盘输出管道，唯一职责将内存流的字节数组写入到本地磁盘
BufferedOutputStream bos =
new BufferedOutputStream(
new FileOutputStream("logo.xlsx"))
){
byte [] buf= new byte[1024];
int length = 0;
//使用URL的输入管道，读取URL的数据
while((length = in.read(buf))!=-1) {
//内存流写入url读取的数据
out.write(buf,0,length);
}
out.flush();
//out.toByteArray()里面存放了百度LOGO的字节数组
//bos.write(out.toByteArray());内存流数据写入本地磁盘
bos.write(out.toByteArray());
bos.flush();
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
参考博客：
java 实现从url路径中下载文件到本地_con.setrequestproperty user-agent-CSDN博客