springMVC攔截器從Request中獲取Json格式並解決request的請求流只能讀取一次的問題
背景
在使用SSM（你問我什麼叫SSM，我一拳錘爆你的狗頭）做開發的時候，經常會使用@RequestBody註解，這個註解是非常的好用。但是如果你想在請求引數傳到後臺的時候做一個引數檢驗，當然可以！使用SpringMVC的攔截器，在攔截器裡把request的資料讀取出來不就行了！！，但是在使用了攔截器的時候會出現一個問題！！！！你在攔截器讀取了request的資料，在Controller裡面@RequestBody註解獲取Json就會失敗就讀取不到資料！！！！那就是RequestBody是流的形式讀取的，流讀取一次就沒有了！！
為什麼使用RequestBody只能讀取一遍請求資料流？
那是因為流對應的是資料，資料放在記憶體中，有的是部分放在記憶體中。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（從記憶體中copy）資料。 所以這就是為什麼讀了一次第二次是空了。 怎麼讓它不為空呢？只要inputstream 中的pos 變成0就可以重寫讀取當前記憶體中的資料。javaAPI中有一個方法public void reset() 這個方法就是可以重置pos為起始位置，但是不是所有的IO讀取流都可以呼叫該方法！ServletInputStream是不能呼叫reset方法，這就導致了只能呼叫一次getInputStream()。
解決辦法：重寫HttpServletRequestWrapper方法
這種方法就是通過重寫HttpServletRequestWrapper把request的儲存下來，然後通過過濾器儲存下來的request在填充進去，這樣就可以多次讀取request了
1.重寫HttpServletRequestWrapper方法
public class RequestWrapper extends HttpServletRequestWrapper {
private final String body;
public RequestWrapper(HttpServletRequest request) throws IOException {
super(request);
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 (bufferedReader != null) {
try {
bufferedReader.close();
} catch (IOException ex) {
throw ex;
}
}
}
body = stringBuilder.toString();
}
@Override
public ServletInputStream getInputStream() throws IOException {
final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes());
ServletInputStream servletInputStream = new ServletInputStream() {
public boolean isFinished() {
return false;
}
public boolean isReady() {
return false;
}
public void setReadListener(ReadListener readListener) {}
public int read() throws IOException {
return byteArrayInputStream.read();
}
};
return servletInputStream;
}
@Override
public BufferedReader getReader() throws IOException {
return new BufferedReader(new InputStreamReader(this.getInputStream()));
}
public String getBody() {
return this.body;
}
}
2.攔截器CommonInterceptor
public class CommonInterceptor extends HandlerInterceptorAdapter {
private final Log log = LogFactory.getLog(CommonInterceptor.class);
public CommonInterceptor() {
}
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
RequestWrapper myRequestWrapper = new RequestWrapper((HttpServletRequest) request);
String body = myRequestWrapper.getBody();
System.out.println("我是攔截器："+body);
// do something
return true;
}
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
super.postHandle(request, response, handler, modelAndView);
}
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
super.afterCompletion(request, response, handler, ex);
}
public void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
super.afterConcurrentHandlingStarted(request, response, handler);
}
}
3.在spring-mvc.xml宣告springMVC的攔截器
<mvc:interceptors>
<mvc:interceptor>
<mvc:mapping path="/**"/>
<bean class="com.sdut.platform.core.CommonInterceptor"/>
</mvc:interceptor>
</mvc:interceptors>
4.過濾器HttpServletFilter類
public class HttpServletFilter implements Filter {
public void init(FilterConfig filterConfig) throws ServletException {
}
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
ServletRequest requestWrapper = null;
System.out.println("我是過濾器");
if(request instanceof HttpServletRequest) {
requestWrapper = new RequestWrapper((HttpServletRequest) request);
}
if(requestWrapper == null) {
chain.doFilter(request, response);
} else {
chain.doFilter(requestWrapper, response);
}
}
public void destroy() {
}
}
5.在web.xml中註冊過濾器
<filter>
<filter-name>requestFilter</filter-name>
<filter-class>com.sdut.platform.core.HttpServletFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>requestFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
經過測試完全可以並且不出現其他錯誤。
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作者：sdut菜鳥
來源：CSDN
原文：https://blog.csdn.net/sdut406/article/details/81369983
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