攔截器獲取HttpServletRequest裏body數據

1、問題

經過在攔截器中獲取request中的json數據，咱們能夠實現對參數進行校驗和改寫。問題是參數只能在攔截器裏獲取一次，日後在controller層就沒法獲取數據，提示body爲空。

在網上查找資料後發現，request的輸入流只能讀取一次，那麼這是爲何呢？

那是由於流對應的是數據，數據放在內存中，有的是部分放在內存中。
read 一次標記一次當前位置（mark position），第二次read就從標記位置繼續讀（從內存中copy）數據。 因此這就是爲何讀了一次第二次是空了。 怎麼讓它不爲空呢？
只要inputstream 中的pos 變成0就能夠重寫讀取當前內存中的數據。javaAPI中有一個方法public void reset() 這個方法就是能夠重置pos爲起始位置，可是不是全部的IO讀取流均可以調用該方法！
ServletInputStream是不能調用reset方法，這就致使了只能調用一次getInputStream()

 

2、解決辦法

HttpServletRequestWrapper是 httpServletRequest 的包裝類

新建一個類繼承HttpServletRequestWrapper實現對 httpServletRequest 的裝飾，用來獲取 body 數據

public class BodyReaderHttpServletRequestWrapper extends HttpServletRequestWrapper {


    private final byte[] body;
    private String bodyStr;

    public BodyReaderHttpServletRequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        String bodyString = getBodyString(request);
        body = bodyString.getBytes(Charset.forName("UTF-8"));
        bodyStr=bodyString;
    }

    public String getBodyStr() {
        return bodyStr;
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body);

        return new ServletInputStream() {
            @Override
            public int read() throws IOException {
                return byteArrayInputStream.read();
            }

            @Override
            public boolean isFinished() {
                return false;
            }

            @Override
            public boolean isReady() {
                return false;
            }

            @Override
            public void setReadListener(ReadListener readListener) {
            }
        };
    }


    public  String getBodyString(HttpServletRequest request) throws IOException {
        StringBuilder sb = new StringBuilder();
        InputStream inputStream = null;
        BufferedReader reader = null;
        try {
            inputStream = request.getInputStream();
            reader = new BufferedReader(
                    new InputStreamReader(inputStream, Charset.forName("UTF-8")));

            char[] bodyCharBuffer = new char[1024];
            int len = 0;
            while ((len = reader.read(bodyCharBuffer)) != -1) {
                sb.append(new String(bodyCharBuffer, 0, len));
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return sb.toString();
    }
}

 

再新建一個 filter 實現對傳入的 httpServletRequest 的轉換

@WebFilter(filterName = "httpServletRequestWrapperFilter", urlPatterns = {"/*"})
public class HttpServletRequestWrapperFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        ServletRequest requestWrapper = null;

        if (request instanceof HttpServletRequest) {
            HttpServletRequest httpRequest = (HttpServletRequest) request;
            //遇到post方法纔對request進行包裝
            String methodType = httpRequest.getMethod();
            if ("POST".equals(methodType)) {
                requestWrapper = new BodyReaderHttpServletRequestWrapper(
                        (HttpServletRequest) request);
            }
        }
        if (null == requestWrapper) {
            chain.doFilter(request, response);
        } else {
            chain.doFilter(requestWrapper, response);
        }
    }

    @Override
    public void destroy() {

    }
}

 

最後在攔截器就能夠獲取request中body數據

if(request instanceof  BodyReaderHttpServletRequestWrapper ){
            System.out.println(((BodyReaderHttpServletRequestWrapper) request).getBodyStr());
        }

經測試發現並不影響controller層獲取body數據

 

爲何須要在 filter 裏進行對 httpServletRequest 的包裝轉換，直接在攔截器裏進行包裝不行嘛？

過濾器（Filter）和攔截器（Interceptor）之間的最大區別就是，過濾器能夠包裝Request和Response，而攔截器並不能

用代碼描述攔截器和過濾器的流程大概就是這樣的：
攔截器：void run () {
    Request request = new Request();

    preHandle(request);

    service(request);
}

preHandler(Request request) {

    request = new RequestWrapper(request);  //在這裏修改Request的引用，不會影響到service方法的request
}

過濾器void run () {
    Request request = new Request();

    doFilter(request);
}

doFilter(Request request) {

    request = new RequestWrapper(request);  //在這裏修改Request的引用，會影響到service方法的request

    service(request);
}