上传文件乱码，GBK转UTF-8

String root = filePath;// 上传路径
File rootFile = new File(root);
// 路径不存在先创建路径
if (!rootFile.exists()) {
rootFile.mkdirs();
}
// 获取后缀type
String suffix = domain.getSuffixName();
// 新文件名
String strNewName = domain.getScriptName().trim() + domain.getVersionName().trim() + "."
+ suffix;
domain.setScriptUrl("/" + strNewName);
File destFile;
String destFilePath=root+"/"+strNewName;
destFile = new File(root, strNewName);
OutputStream outputStream;
outputStream = new FileOutputStream(destFile);
// file是上传过来的文件，存放为临时tmp
File file = domain.getFile();

String context = "";
InputStreamReader isr;
isr = new InputStreamReader(new FileInputStream(file), "GBK");
BufferedReader br = new BufferedReader(isr);
String line;

while ((line = br.readLine()) != null) {
context += line + "\r\n";
System.out.println(line);
}

br.close();

byte[] content = context.getBytes();
context = new String(content, "UTF-8");

BufferedWriter writer;

FileOutputStream fos = new FileOutputStream(destFilePath, true);
System.out.println(root+"/"+strNewName);
writer = new BufferedWriter(new OutputStreamWriter(fos, "UTF-8"));
writer.append(context);
writer.close();