添加pdf的第一页图片资源，缓存到app目录中，保存路径到数据库。

app/src/main/java/com/all/pdfreader/pro/app/util/PdfScanner.kt

@@ -1,12 +1,18 @@
 package com.all.pdfreader.pro.app.util
 
 import android.content.Context
+import android.graphics.Bitmap
+import android.graphics.pdf.PdfRenderer
+import android.os.ParcelFileDescriptor
 import android.util.Log
 import com.all.pdfreader.pro.app.room.entity.PdfDocumentEntity
 import com.all.pdfreader.pro.app.room.repository.PdfRepository
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
+import java.io.File
+import java.io.FileOutputStream
 import java.util.concurrent.TimeUnit
+import androidx.core.graphics.createBitmap
 
 class PdfScanner(
     private val context: Context,
@@ -55,6 +61,8 @@ class PdfScanner(
 
                             if (existingDoc == null) {
                                 LogUtil.logDebug("ocean", "PdfScanner:    🆕 发现新PDF文件: ${file.name}")
+                                val thumbnailPath = generateThumbnail(context, file)
+
                                 val metadata =
                                     PdfMetadataExtractor.extractMetadata(file.absolutePath)
                                 val document = PdfDocumentEntity(
@@ -64,6 +72,7 @@ class PdfScanner(
                                     fileSize = file.length(),
                                     lastModified = file.lastModified(),
                                     pageCount = metadata?.pageCount ?: 0,
+                                    thumbnailPath = thumbnailPath,
                                     metadataTitle = metadata?.title,
                                     metadataAuthor = metadata?.author,
                                     metadataSubject = metadata?.subject,
@@ -124,4 +133,41 @@ class PdfScanner(
         val lastScan = getLastScanTime()
         return TimeUnit.MILLISECONDS.toHours(System.currentTimeMillis() - lastScan)
     }
+
+
+    private fun generateThumbnail(context: Context, pdfFile: File): String? {
+        return try {
+            val fileDescriptor = ParcelFileDescriptor.open(pdfFile, ParcelFileDescriptor.MODE_READ_ONLY)
+            val pdfRenderer = PdfRenderer(fileDescriptor)
+
+            if (pdfRenderer.pageCount > 0) {
+                val page = pdfRenderer.openPage(0)
+                val bitmap = createBitmap(page.width, page.height)
+                page.render(bitmap, null, null, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY)
+                page.close()
+
+                // 保存到缓存目录
+                val cacheDir = File(context.cacheDir, "thumbnails")
+                if (!cacheDir.exists()) cacheDir.mkdirs()
+                val thumbFile = File(cacheDir, pdfFile.nameWithoutExtension + ".jpg")
+
+                FileOutputStream(thumbFile).use { out ->
+                    bitmap.compress(Bitmap.CompressFormat.JPEG, 80, out)
+                }
+
+                pdfRenderer.close()
+                fileDescriptor.close()
+
+                thumbFile.absolutePath
+            } else {
+                pdfRenderer.close()
+                fileDescriptor.close()
+                null
+            }
+        } catch (e: Exception) {
+            e.printStackTrace()
+            null
+        }
+    }
+
 }