从OutputStream转String

一、InputStream转Map

我们在处理请求体时，会将请求体读取成InputStream流，这时我们经常需要将流转成Map，这里就以HttpServletRequest的过滤器为例。

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

/**
* 将InputStream转成Map
* 
* @param inputStream
*            请求流
* @param contentType
*            Content-Type
* @return Map 对象
* @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转文件

将OutputStream转成文件在日常开发中是十分常见的需求，这里给出一个方法实现。

/**
* 将OutputStream流写入文件
* 
* @param outputStream
*            源流
* @param filePath
*            目标文件路径
* @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编码

在将OutputStream转成String时，要注意编码格式，否则可能会出现乱码的情况。

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一般是作为写入数据的流，默认将数据写入到流中，然后再从流中读取到另一段进行处理。

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

// 网络流
OutputStream outputStream = socket.getOutputStream();

五、OutputStream用于

OutputStream主要用于将数据写入到指定的流中，常见的有文件流和网络流。