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Spring Boot Generic File Service
Es ist schon erstaunlich wie man auch mit Spring Boot REST Services generisch und allgemein basierend auf der Servlet Schnittstelle programmieren kann. Das folgende Programmscript zeigt den REST Controller GenericFileService mit dem wir anhand des Path URL Parameters eine lokale Datei laden und Buffered an den HTTP Client transferieren.
package ch.std.fileservice.rest;
import java.io.FileInputStream;
import java.io.OutputStream;
import java.net.URLConnection;
import javax.activation.MimetypesFileTypeMap;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@RequestMapping(value = "/rest/file")
public class GenericFileService {
public GenericFileService() {
super();
}
@GetMapping
public void get(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
String path = httpServletRequest.getParameter("path");
if (path == null) {
httpServletResponse.setContentType("text/html; charset=UTF-8");
httpServletResponse.getWriter().print("path is missing");
return;
}
String mimeType = URLConnection.guessContentTypeFromName(path);
if (mimeType == null) {
MimetypesFileTypeMap mimeTypesMap = new MimetypesFileTypeMap();
mimeType = mimeTypesMap.getContentType(path);
}
httpServletResponse.setContentType(mimeType);
httpServletResponse.setHeader("Transfer-Encoding", "chunked");
OutputStream os = httpServletResponse.getOutputStream();
byte[] buffer = new byte[1 << 12];
int bytesRead = -1;
try (FileInputStream fis = new FileInputStream(path)) {
while ((bytesRead = fis.read(buffer)) > 0) {
os.write(buffer, 0, bytesRead);
os.flush();
}
} catch (Exception e) {
httpServletResponse.setContentType("text/html; charset=UTF-8");
os.write(("path " + path + " does not exist").getBytes(StandardCharsets.UTF_8));
os.flush();
}
return;
}
}
package ch.std.fileservice;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class GenericFileServiceApplication {
public static void main(String[] args) {
SpringApplication.run(GenericFileServiceApplication.class, args);
}
}
Nach dem Start der Spring Boot Applikation ist der File Service aktiv und kann je nach Konfiguration wie folgt adressiert werden:
http://localhost:8080/rest/file?path=/mypath/myfile.txt
Sofern das File existiert wird es zum Client gestreamt.
Das folgende Listing zeigt den dazu passenden Spring Boot File Service Client entwickelt als Command Line Applikation:
package ch.std.fileservice.client;
import java.io.FileOutputStream;
import java.net.URL;
import java.util.Arrays;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.WebApplicationType;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.http.converter.ByteArrayHttpMessageConverter;
import org.springframework.web.client.RestTemplate;
@SpringBootApplication
public class GenericFileServiceClient implements ApplicationRunner {
public static void main(String[] args) throws Exception {
SpringApplication app = new SpringApplication(GenericFileServiceClient.class);
app.setWebApplicationType(WebApplicationType.NONE);
app.run(args);
}
@Override
public void run(ApplicationArguments args) throws Exception {
URL url = null;
try {
url = new URL(args.getOptionValues("url").get(0));
} catch (Exception e) {
System.err.println("missing --url option argument");
this.help();
return;
}
String out = null;
try {
out = args.getOptionValues("out").get(0);
} catch (Exception e) {
}
RestTemplate restTemplate = new RestTemplate();
restTemplate.getMessageConverters().add(new ByteArrayHttpMessageConverter());
HttpHeaders headers = new HttpHeaders();
HttpEntity entity = new HttpEntity(headers);
ResponseEntity response = restTemplate.exchange(url.toString(), HttpMethod.GET, entity, byte[].class, "1");
if (out != null) {
try (FileOutputStream fos = new FileOutputStream(out)) {
fos.write(response.getBody());
}
System.out.println("result written to file " + out);
}
private void help() {
System.out.println("usage java -jar genericfileclient-0.0.1-SNAPSHOT.jar --url= --out=");
System.out.println("example:");
System.out.println("java -jar genericfileclient-0.0.1-SNAPSHOT.jar --url=http://localhost:8080/rest/file?path=in/bigimage.jpg --out=out/bigimage.jpg");
}
}
Client und Service sind am besten in 2 separaten Spring Boot Projekten zu programmieren z.B. mit der Eclipse IDE.
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