Java post请求发送json数据在filter中解析方法

原文地址：http://blog.csdn.net/kyunchen/article/details/55652160

大家都知道Java的servlet分get和post请求方式，在servlet或者在集成了springMVC、Struts2的框架的情况下获取请求的参数。那么有时候我们需要在拦截其中获取ServletRequest的参数就不那么容易了。因为在ServletRequst中，如果是get请求我们可以通过request.getParameter（“”）来获取get的参数或者是form提交的post参数，但是如果是ajax提交的post请求的application/json请求，那么在get的时候就无法获取到值了，有人会想我通过request的请求流来解析json文本，这样做是可以的，但 是有个问题就是如果在拦截其中调用了ServletRequest的getInputStream方法，那么在后面的servlet中或者你集成的框架中的control层就无法调用getInputStream方法来解析获取参数了。
有了上面的疑问，我们就有了分析，解决办法的途径。通过对HttpServletRequest的分析结合资料，最后得出结论就是改写ServletRequst的getInputStream方法便可以解决问题。我们可以分析一下HttpServletRequest的中的stream只能被read一次，那么我们可以在filter中调用getInputSteam获取json字符串，然后通过获取的json文本去生成新的stream来给ServletRequest，后面的control就可以继续获取stream（我们自己用json文本生成）。有了这个思路我们就来看看代码。
第一部分，改写ServletRequest：

public class PostServletRequest extends HttpServletRequestWrapper{    private String body=null;    /**     * Constructs a request object wrapping the given request.     * @param request     * @throws IllegalArgumentException if the request is null     */    public PostServletRequest(HttpServletRequest request,String body) {        super(request);        this.body=body;    }    @Override    public ServletInputStream getInputStream() throws IOException {        ServletInputStream inputStream = null;        if(StringUtil.isNotEmpty(body)){            inputStream =  new PostServletInputStream(body);        }        return inputStream;    }    @Override    public BufferedReader getReader() throws IOException {        String enc = getCharacterEncoding();        if(enc == null) enc = "UTF-8";        return new BufferedReader(new InputStreamReader(getInputStream(), enc));    }}

第二本分，ServletInputStream的改写：

public class PostServletInputStream  extends ServletInputStream {    private InputStream inputStream;    private String body ;//解析json之后的文本    public PostServletInputStream(String body) throws IOException {        this.body=body;        inputStream = null;    }    private InputStream acquireInputStream() throws IOException {        if(inputStream == null) {            inputStream = new ByteArrayInputStream(body.getBytes());//通过解析之后传入的文本生成inputStream以便后面control调用        }        return inputStream;    }    public void close() throws IOException {        try {            if(inputStream != null) {                inputStream.close();            }        }        catch(IOException e) {            throw e;        }        finally {            inputStream = null;        }    }    public int read() throws IOException {        return acquireInputStream().read();    }    public boolean markSupported() {        return false;    }    public synchronized void mark(int i) {        throw new UnsupportedOperationException("mark not supported");    }    public synchronized void reset() throws IOException {        throw new IOException(new UnsupportedOperationException("reset not supported"));    }}

第三部分：在filter中的调用

//解析post的json参数String body = getBody((HttpServletRequest)request);Map paramMap = JsonUtil.json2Map(body);if(null != paramMap){    wpcCd = (String)paramMap.get("wpcCd");}//使用解析数据重新生成ServletRequest，供doChain调用request =getRequest(request,body);getBody方法：private String getBody(HttpServletRequest request) throws IOException {        String body = null;        StringBuilder stringBuilder = new StringBuilder();        BufferedReader bufferedReader = null;        try {            InputStream inputStream = request.getInputStream();            if (inputStream != null) {                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));                char[] charBuffer = new char[128];                int bytesRead = -1;                while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {                    stringBuilder.append(charBuffer, 0, bytesRead);                }            } else {                stringBuilder.append("");            }        } catch (IOException ex) {            throw ex;        }finally {            if(null != bufferedReader){                bufferedReader.close();            }        }        body = stringBuilder.toString();        return body;    }    /**     * 将post解析过后的request进行封装改写     * @param request     * @param body     * @return     */    private ServletRequest getRequest(ServletRequest request ,String body){        String enctype = request.getContentType();        if (StringUtils.isNotEmpty(enctype) && enctype.contains("application/json")){            return new PostServletRequest((HttpServletRequest) request,body);        }        return request;    }

如果在其他地方也有用到类似，可根据实际应用自己封装改写getInputStream即可。到此结束。谢谢！