Support file downloading in Java jersey2 client

modules/swagger-codegen/src/main/resources/Java/libraries/jersey2/ApiClient.mustache

@@ -20,6 +20,9 @@ import org.glassfish.jersey.media.multipart.FormDataContentDisposition;
 import org.glassfish.jersey.media.multipart.MultiPart;
 import org.glassfish.jersey.media.multipart.MultiPartFeature;
 
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Files;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Map;
@@ -37,6 +40,8 @@ import java.io.UnsupportedEncodingException;
 
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import {{invokerPackage}}.auth.Authentication;
 import {{invokerPackage}}.auth.HttpBasicAuth;
@@ -52,6 +57,7 @@ public class ApiClient {
 
   private Client httpClient;
   private JSON json;
+  private String tempFolderPath = null;
 
   private Map<String, Authentication> authentications;
 
@@ -235,6 +241,22 @@ public class ApiClient {
     return this;
   }
 
+  /**
+   * The path of temporary folder used to store downloaded files from endpoints
+   * with file response. The default value is <code>null</code>, i.e. using
+   * the system's default tempopary folder.
+   *
+   * @see https://docs.oracle.com/javase/7/docs/api/java/io/File.html#createTempFile(java.lang.String,%20java.lang.String,%20java.io.File)
+   */
+  public String getTempFolderPath() {
+    return tempFolderPath;
+  }
+
+  public ApiClient setTempFolderPath(String tempFolderPath) {
+    this.tempFolderPath = tempFolderPath;
+    return this;
+  }
+
   /**
   * Connect timeout (in milliseconds).
    */
@@ -467,6 +489,13 @@ public class ApiClient {
    * Deserialize response body to Java object according to the Content-Type.
    */
   public <T> T deserialize(Response response, GenericType<T> returnType) throws ApiException {
+    // Handle file downloading.
+    if (returnType.equals(File.class)) {
+      @SuppressWarnings("unchecked")
+      T file = (T) downloadFileFromResponse(response);
+      return file;
+    }
+
     String contentType = null;
     List<Object> contentTypes = response.getHeaders().get("Content-Type");
     if (contentTypes != null && !contentTypes.isEmpty())
@@ -477,6 +506,55 @@ public class ApiClient {
     return response.readEntity(returnType);
   }
 
+  /**
+   * Download file from the given response.
+   * @throws ApiException If fail to read file content from response and write to disk
+   */
+  public File downloadFileFromResponse(Response response) throws ApiException {
+    try {
+      File file = prepareDownloadFile(response);
+      Files.copy(response.readEntity(InputStream.class), file.toPath());
+      return file;
+    } catch (IOException e) {
+      throw new ApiException(e);
+    }
+  }
+
+  public File prepareDownloadFile(Response response) throws IOException {
+    String filename = null;
+    String contentDisposition = (String) response.getHeaders().getFirst("Content-Disposition");
+    if (contentDisposition != null && !"".equals(contentDisposition)) {
+      // Get filename from the Content-Disposition header.
+      Pattern pattern = Pattern.compile("filename=['\"]?([^'\"\\s]+)['\"]?");
+      Matcher matcher = pattern.matcher(contentDisposition);
+      if (matcher.find())
+        filename = matcher.group(1);
+    }
+
+    String prefix = null;
+    String suffix = null;
+    if (filename == null) {
+      prefix = "download-";
+      suffix = "";
+    } else {
+      int pos = filename.lastIndexOf(".");
+      if (pos == -1) {
+        prefix = filename + "-";
+      } else {
+        prefix = filename.substring(0, pos) + "-";
+        suffix = filename.substring(pos);
+      }
+      // File.createTempFile requires the prefix to be at least three characters long
+      if (prefix.length() < 3)
+        prefix = "download-";
+    }
+
+    if (tempFolderPath == null)
+      return File.createTempFile(prefix, suffix);
+    else
+      return File.createTempFile(prefix, suffix, new File(tempFolderPath));
+  }
+
   /**
    * Invoke API by sending HTTP request with the given options.
    *