一、错误演示

• 当客户端发送一个参数为JSON的请求时，我现在想使用拦截器先将它拦截并缓存起来，但是发现拦截器拦截之后，请求就无法再一次获取到数据，如下：

1. 创建项目，添加所需依赖

	<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

2. 配置redis环境

server.port=8888
spring.redis.port=6379
spring.redis.host=localhost

3. 写一个简单的测试请求

@RestController
public class HelloController {

    @PostMapping("/hello")
    public String hello(@RequestBody String json) {
        return json;
    }
}

4. 写一个拦截器，拦截请求

@Component
public class RepeatSubmitInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String s = request.getReader().readLine();
        System.out.println("request.getReader().readLine()= " + s);
        return true;
    }

}

5. WebConfig 注册拦截器

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Autowired
    RepeatSubmitInterceptor repeatSubmitInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(repeatSubmitInterceptor).addPathPatterns("/**");
    }
}

6. 测试请求

二、问题解决

采用一个装饰者模式，将请求重新包装一下

1. 创建 RepeatableReadRequestWrapper 类，包装请求

public class RepeatableReadRequestWrapper extends HttpServletRequestWrapper {

    private final byte[] bytes;

    public RepeatableReadRequestWrapper(HttpServletRequest request, HttpServletResponse response) throws IOException {
        super(request);
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        bytes = request.getReader().readLine().getBytes();
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        ByteArrayInputStream bi = new ByteArrayInputStream(bytes);
        return new ServletInputStream() {
            @Override
            public boolean isFinished() {
                return false;
            }

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

            @Override
            public void setReadListener(ReadListener readListener) {

            }

            @Override
            public int read() throws IOException {
                return bi.read();
            }

            @Override
            public int available() throws IOException {
                return bytes.length;
            }
        };
    }

    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(getInputStream()));
    }
}

2. 创建 RepeatableRequestFilter 过滤器，过滤器在拦截器之前执行，如果请求参数为JSON，则包装请求

public class RepeatableRequestFilter implements Filter {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        if (StringUtils.startsWithIgnoreCase(request.getContentType(),"application/json")){
            RepeatableReadRequestWrapper requestWrapper = new RepeatableReadRequestWrapper(request, response);
            filterChain.doFilter(requestWrapper,response);
            return;
        }
        filterChain.doFilter(request,response);
    }
}

3. WebConfig 注册过滤器

@Bean
    FilterRegistrationBean<RepeatableRequestFilter> repeatableRequestFilterFilterRegistrationBean(){
        FilterRegistrationBean<RepeatableRequestFilter> bean = new FilterRegistrationBean<>();
        bean.setFilter(new RepeatableRequestFilter());
        bean.addUrlPatterns("/*");
        return bean;
    }

4. 再次测试

这样，就解决了请求参数为JSON时，采用IO流读取，只能请求一次的问题。
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