1.优化代码结构，抽象预览接口服务

2.新增更多图片预览格式支持

jodconverter-web/src/main/java/cn/keking/service/FilePreviewFactory.java

@@ -0,0 +1,30 @@
+package cn.keking.service;
+
+import cn.keking.model.FileAttribute;
+import cn.keking.utils.FileUtils;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ApplicationContext;
+import org.springframework.stereotype.Service;
+import org.springframework.ui.Model;
+
+import java.util.Map;
+
+/**
+ * Created by kl on 2018/1/17.
+ * Content :
+ */
+@Service
+public class FilePreviewFactory {
+
+    @Autowired
+    FileUtils fileUtils;
+
+    @Autowired
+    ApplicationContext context;
+
+    public FilePreview get(String url) {
+        Map<String, FilePreview> filePreviewMap = context.getBeansOfType(FilePreview.class);
+        FileAttribute fileAttribute = fileUtils.getFileAttribute(url);
+        return filePreviewMap.get(fileAttribute.getType().getInstanceName());
+    }
+}