Add workflow bpmn file preview support (#441)

server/src/main/java/cn/keking/service/impl/CommonPreviewImpl.java

@@ -0,0 +1,48 @@
+package cn.keking.service.impl;
+
+import cn.keking.model.FileAttribute;
+import cn.keking.model.ReturnResponse;
+import cn.keking.service.FileHandlerService;
+import cn.keking.service.FilePreview;
+import cn.keking.utils.DownloadUtils;
+import cn.keking.utils.KkFileUtils;
+import org.springframework.stereotype.Component;
+import org.springframework.stereotype.Service;
+import org.springframework.ui.Model;
+import org.springframework.util.CollectionUtils;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Created by kl on 2018/1/17.
+ * Content :图片文件处理
+ */
+@Component("commonPreview")
+public class CommonPreviewImpl implements FilePreview {
+
+    private final FileHandlerService fileHandlerService;
+    private final OtherFilePreviewImpl otherFilePreview;
+
+    public CommonPreviewImpl(FileHandlerService fileHandlerService, OtherFilePreviewImpl otherFilePreview) {
+        this.fileHandlerService = fileHandlerService;
+        this.otherFilePreview = otherFilePreview;
+    }
+
+    @Override
+    public String filePreviewHandle(String url, Model model, FileAttribute fileAttribute) {
+        // 不是http开头，浏览器不能直接访问，需下载到本地
+        if (url != null && !url.toLowerCase().startsWith("http")) {
+            ReturnResponse<String> response = DownloadUtils.downLoad(fileAttribute, null);
+            if (response.isFailure()) {
+                return otherFilePreview.notSupportedFile(model, fileAttribute, response.getMsg());
+            } else {
+                String file = fileHandlerService.getRelativePath(response.getContent());
+                model.addAttribute("currentUrl", file);
+            }
+        } else {
+            model.addAttribute("currentUrl", url);
+        }
+        return null;
+    }
+}