我们正在使用PKCS7签名，并使用客户端上创建的签名在服务器上签名文档。我们在内存中创建Pdf对象，并希望切换到我们不需要依赖系统内存的系统。目前，我正在保存在会话中生成哈希时创建的PdfSignatureAppearance对象，然后在我从客户端收到响应时使用此会话（签名哈希内容）。你能帮我找出一种方法，我不需要在会话中保存PdfSignatureAppearance对象，可以直接使用Temp文件进行签名吗？
首先，我们在插入签名外观后生成文件哈希，如下面的代码所示：
File file = new File("To be signed file location")
char version = '\u0000'
ByteArrayOutputStream out = new ByteArrayOutputStream()
String outputFile = "Signed file name"
FileOutputStream fileOutputStream = new FileOutputStream(outputFile)
PdfReader pdfReader = new PdfReader(new FileInputStream(file.absolutePath))
PdfStamper stamper = new PdfStamper(pdfReader, out, version, true)
PdfFormField pdfFormField = PdfFormField.createSignature(stamper.getWriter())
String signatureName = "Signature1"
pdfFormField.setWidget(new Rectangle((float) 20, (float) 20, (float) 100, (float) 60), (PdfName) null)
pdfFormField.setFlags(4)
pdfFormField.put(PdfName.DA, new PdfString("/Helv 0 Tf 0 g"))
pdfFormField.setFieldName(signatureName)
pdfFormField.setPage(1)
stamper.addAnnotation(pdfFormField, i)
stamper.close()
pdfReader = new PdfReader(out.toByteArray())
stamper = PdfStamper.createSignature(pdfReader, fileOutputStream, version, (File) null, true)
PdfSignatureAppearance appearance = stamper.getSignatureAppearance()
appearance.setLayer2Text("Digitally Signed by Name")
appearance.setImage(Image.getInstance(esignRequestCO.logoLocation))
appearance.setAcro6Layers(true)
Calendar cal = Calendar.getInstance()
cal.setTime(new Date())
cal.add(12, 5)
appearance.setSignDate(cal)
appearance.setVisibleSignature(signatureName)
int contentEstimated = 16384
HashMap<PdfName, Integer> exc = new HashMap()
exc.put(PdfName.CONTENTS, contentEstimated * 2 + 2)
PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED)
dic.setReason(appearance.getReason())
dic.setLocation(appearance.getLocation())
dic.setDate(new PdfDate(appearance.getSignDate()))
appearance.setCryptoDictionary(dic)
appearance.preClose(exc)
InputStream inp = appearance.getRangeStream()
byte[] bytes = IOUtils.toByteArray(inp)
String hash = DigestUtils.sha256Hex(bytes)
只要我们获得签名内容，我们就会使用相同的外观对象在文件中插入内容，如下所示：
int contentEstimated = 16384
PdfSignatureAppearance appearance = "PdfSignatureAppearance object from session generated in previous step"
byte[] p7barray = "signed content here".bytes
byte[] paddedSig = new byte[contentEstimated]
System.arraycopy(p7barray, 0, paddedSig, 0, p7barray.length)
PdfDictionary dic2 = new PdfDictionary()
dic2.put(PdfName.CONTENTS, (new PdfString(paddedSig)).setHexWriting(true))
appearance.close(dic2)