java map转Multipart/form-data类型body

public static String mapToTxt(Map<String,String> fieldMap, Map<String,File> fileMap,String fileName) throws Exception{
		Random random = new Random();
		int j;
		String getLine = "\r\n";
		String fileType = "Content-Type: application/octet-stream";
		String doubleBar = "--";
		biaoshi = "----WebKitFormBoundary";
		StringBuffer sb = new StringBuffer();
		for(int i = 0; i < 16;i++){
			j = random.nextInt(MULTIPART_CHARS.length-2)+2;
			sb.append(MULTIPART_CHARS[j]);
		}
		biaoshi = biaoshi + sb.toString();
		StringBuffer stringBuffer = new StringBuffer();



		for (Map.Entry<String,String> entity:fieldMap.entrySet()) {
			String name = "Content-Disposition: form-data; name=\""+entity.getKey()+"\"";
			stringBuffer.append(doubleBar+biaoshi);
			stringBuffer.append(getLine);
			stringBuffer.append(name);
			stringBuffer.append(getLine);
			stringBuffer.append(getLine);
			stringBuffer.append(entity.getValue());
			stringBuffer.append(getLine);
		}

		for (Map.Entry<String,File> entity:fileMap.entrySet()) {
			String name = "Content-Disposition: form-data; name=\""+fileName+"\"; filename=\""+entity.getValue().getName()+"\"";
			stringBuffer.append(doubleBar+biaoshi);
			stringBuffer.append(getLine);
			stringBuffer.append(name);
			stringBuffer.append(getLine);
			stringBuffer.append(fileType);
			stringBuffer.append(getLine);
			stringBuffer.append(getLine);
			File f = entity.getValue();
			FileInputStream fileInputStream = new FileInputStream(f);
			ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
			byte by[] = new byte[1024];
			int k = 0;
			while ((k=fileInputStream.read(by))!=-1){
				byteArrayOutputStream.write(by,0,k);
			}
			by = byteArrayOutputStream.toByteArray();
			for(int i = 0; i < by.length; i++){
				stringBuffer.append(by[i]);
			}
			stringBuffer.append(getLine);
		}
		stringBuffer.append(doubleBar+biaoshi+doubleBar);
		return stringBuffer.toString();
	}