I have 3 machines:

1. server where the file is located
   
2. server where REST service is running ( Jersey)
   
3. client(browser) with access to 2nd server but no access to 1st server

final FTDClient client = FTDClient.getInstance();

try {
    final InputStreamFromOutputStream <String> isOs = new InputStreamFromOutputStream <String>() {
        @Override
        public String produce(final OutputStream dataSink) throws Exception {
            return client.downloadFile2(location, Integer.valueOf(spaceId), URLDecoder.decode(filePath, "UTF-8"), dataSink);
        }
    };
    try {
        String fileName = filePath.substring(filePath.lastIndexOf("/") + 1);

        StreamingOutput output = new StreamingOutput() {
            @Override
            public void write(OutputStream outputStream) throws IOException, WebApplicationException {
                int length;
                byte[] buffer = new byte[1024];
                while ((length = isOs.read(buffer)) != -1) {
                    outputStream.write(buffer, 0, length);
                }
                outputStream.flush();
            }
        };
        return Response.ok(output, MediaType.APPLICATION_OCTET_STREAM)
            .header("Content-Disposition", "attachment; filename=\"" + fileName + "\"")
            .build();
    }
}

ByteArrayOutputStream baos = new ByteArrayOutputStream(2048) ;
client.downloadFile(location, spaceId, filePath, baos);
return Response.ok(baos).build();

最佳答案

"How can I directly (without saving the file on 2nd server) download the file from 1st server to client's machine?"

Client client = ClientBuilder.newClient();
String url = "...";
final InputStream responseStream = client.target(url).request().get(InputStream.class);

Response response = client.target(url).request().get();
InputStream is = (InputStream)response.getEntity();

From 2nd server I can get a ByteArrayOutputStream to get the file from 1st server, can I pass this stream further to the client using the REST service?

final InputStream responseStream = client.target(url).request().get(InputStream.class);
System.out.println(responseStream.getClass());
StreamingOutput output = new StreamingOutput() {
    @Override
    public void write(OutputStream out) throws IOException, WebApplicationException {  
        int length;
        byte[] buffer = new byte[1024];
        while((length = responseStream.read(buffer)) != -1) {
            out.write(buffer, 0, length);
        }
        out.flush();
        responseStream.close();
    }   
};
return Response.ok(output).header(
        "Content-Disposition", "attachment, filename=\"...\"").build();

final InputStream responseStream = client.target(url).request().get(InputStream.class);
return Response.ok(responseStream).header(
        "Content-Disposition", "attachment, filename=\"...\"").build();

 public static void writeTo(InputStream in, OutputStream out) throws IOException {
    int read;
    final byte[] data = new byte[BUFFER_SIZE];
    while ((read = in.read(data)) != -1) {
        out.write(data, 0, read);
    }
}

WebTarget target = client.target(url);
InputStream is = target.request().get(InputStream.class);

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;

@Provider
public class OutputStreamWriter implements MessageBodyWriter<ByteArrayOutputStream> {

    @Override
    public boolean isWriteable(Class<?> type, Type genericType,
            Annotation[] annotations, MediaType mediaType) {
        return ByteArrayOutputStream.class == type;
    }

    @Override
    public long getSize(ByteArrayOutputStream t, Class<?> type, Type genericType,
            Annotation[] annotations, MediaType mediaType) {
        return -1;
    }

    @Override
    public void writeTo(ByteArrayOutputStream t, Class<?> type, Type genericType,
            Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream)
            throws IOException, WebApplicationException {
        t.writeTo(entityStream);
    }
}

return Response.ok(baos).build();

@Path("test")
public class TestResource {

    final String path = "some_150_mb_file";

    @GET
    @Produces(MediaType.APPLICATION_OCTET_STREAM)
    public Response doTest() throws Exception {
        InputStream is = new FileInputStream(path);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        int len;
        byte[] buffer = new byte[4096];
        while ((len = is.read(buffer, 0, buffer.length)) != -1) {
            baos.write(buffer, 0, len);
        }
        System.out.println("Server size: " + baos.size());
        return Response.ok(baos).build();
    }
}

public class Main {
    public static void main(String[] args) throws Exception {
        Client client = ClientBuilder.newClient();
        String url = "http://localhost:8080/api/test";
        Response response = client.target(url).request().get();
        String location = "some_location";
        FileOutputStream out = new FileOutputStream(location);
        InputStream is = (InputStream)response.getEntity();
        int len = 0;
        byte[] buffer = new byte[4096];
        while((len = is.read(buffer)) != -1) {
            out.write(buffer, 0, len);
        }
        out.flush();
        out.close();
        is.close();
    }
}

StreamingOutput output = new StreamingOutput() {
    @Override
    public void write(OutputStream out) {
        thirdPartyApi.downloadFile(.., .., .., out);
    }
}
return Response.ok(output).build();

关于java - 如何使用 Java REST 服务和数据流下载文件，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29712554/