從OutputStream轉String

一、InputStream轉Map

我們在處理請求體時，會將請求體讀取成InputStream流，這時我們經常需要將流轉成Map，這裡就以HttpServletRequest的過濾器為例。

public void doFilter(ServletRequest req, ServletResponse res,
            FilterChain chain) throws IOException, ServletException {
    HttpServletRequest request = (HttpServletRequest) req;
    // 將inputStream轉成Map
    Map<String, String> paramMap = getParameterMap(request.getInputStream(),
                request.getContentType());
    // do something
    chain.doFilter(req, res);
}

/**
* 將InputStream轉成Map
* 
* @param inputStream
*            請求流
* @param contentType
*            Content-Type
* @return Map 對象
* @throws UnsupportedEncodingException
* @throws IOException
*/
@SuppressWarnings("rawtypes")
private Map<String, String> getParameterMap(InputStream inputStream,
            String contentType) throws UnsupportedEncodingException, IOException {
    Map<String, String> paramMap = new HashMap<String, String>();
    if (contentType != null && contentType.contains("multipart/form-data")) {
        DiskFileItemFactory fileItemFactory = new DiskFileItemFactory();
        ServletFileUpload servletFileUpload = new ServletFileUpload(fileItemFactory);
        try {
            List fileItems = servletFileUpload.parseRequest(new ServletRequestContext(request));
            Iterator it = fileItems.iterator();
            while (it.hasNext()) {
                FileItem fileItem = (FileItem) it.next();
                if (fileItem.isFormField()) {
                    paramMap.put(fileItem.getFieldName(), fileItem.getString());
                }
            }

        } catch (FileUploadException e) {
            LOG.error("Get parameter map failed! ", e);
        }
    } else {
        byte[] body = IOUtils.readFully(inputStream, -1, false);
        paramMap = JsonParserUtils.toMap(new String(body, "UTF-8"));
    }

    return paramMap;
}

二、OutputStream轉文件

將OutputStream轉成文件在日常開發中是十分常見的需求，這裡給出一個方法實現。

/**
* 將OutputStream流寫入文件
* 
* @param outputStream
*            源流
* @param filePath
*            目標文件路徑
* @throws IOException
*/
public static void outputStreamToFile(OutputStream outputStream, String filePath)
            throws IOException {
    byte[] buffer = new byte[1024];
    int len;
    FileOutputStream fos = null;
    try {
        fos = new FileOutputStream(filePath);
        while ((len = outputStream.read(buffer)) != -1) {
            fos.write(buffer, 0, len);
        }
        fos.flush();
    } finally {
        if (fos != null) {
            fos.close();
        }
    }
}

三、OutputStream編碼

在將OutputStream轉成String時，要注意編碼格式，否則可能會出現亂碼的情況。

OutputStream outputStream = new ByteArrayOutputStream();
try {
    outputStream.write("你好".getBytes("UTF-8"));
} catch (IOException e) {
    e.printStackTrace();
}

String result = outputStream.toString("UTF-8");
System.out.println(result);

四、OutputStream用法

OutputStream一般是作為寫入數據的流，默認將數據寫入到流中，然後再從流中讀取到另一段進行處理。

// 文件流
OutputStream outputStream = new FileOutputStream(new File("output.txt"));

// 網絡流
OutputStream outputStream = socket.getOutputStream();

五、OutputStream用於

OutputStream主要用於將數據寫入到指定的流中，常見的有文件流和網絡流。