在 Spring Boot 中使用 Filter

Filter 是Web开发中的利器，可以非常方便的让我们切入功能功能到系统中去。本文演示如何在Spring Boot中定义，使用Filter。

本文中使用 Spring Boot 构建Rest服务实验手册(一) 中的案例进行演示。

新建一个Filter

新建一个名为: cn.com.hohistar.spbt.todoapi.config.filter 的包，在包中新建一个名为: PerfsFilter 的类，代码如下:

@Component
@Order(1)
public class PerfsFilter implements Filter {

    private static final Logger LOG = LoggerFactory.getLogger(PerfsFilter.class);

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        long start = System.currentTimeMillis();

        filterChain.doFilter(servletRequest, servletResponse);

        long end = System.currentTimeMillis();

        LOG.info("url {}, exection time is: {}ms", ((HttpServletRequest)servletRequest).getRequestURL().toString(), (end - start));
    }
}

改变HTTP返回数据

获取返回数据

public class ResultWrapper extends HttpServletResponseWrapper {

    private ByteArrayOutputStream buffer;

    private ServletOutputStream out;

    public ResultWrapper(HttpServletResponse httpServletResponse) {
        super(httpServletResponse);
        buffer = new ByteArrayOutputStream();
        out = new WrapperOutputStream(buffer);
    }

    @Override
    public ServletOutputStream getOutputStream() throws IOException {
        return out;
    }

    @Override
    public void flushBuffer() throws IOException {
        if (out != null) {
            out.flush();
        }
    }

    public byte[] getContent() throws IOException {
        flushBuffer();
        return buffer.toByteArray();
    }


    class WrapperOutputStream extends ServletOutputStream {
        private ByteArrayOutputStream bos;

        public WrapperOutputStream(ByteArrayOutputStream bos) {
            this.bos = bos;
        }

        @Override
        public void write(int b) throws IOException {
            bos.write(b);
        }

        @Override
        public boolean isReady() {

            return false;
        }

        @Override
        public void setWriteListener(WriteListener arg0) {
        }
    }
}

添加统一格式

@Component
public class ResultFilter implements Filter {

    private static final Logger LOG = LoggerFactory.getLogger(ResultFilter.class);

    private static final String API_RESULT = "{\"succ\":true,\"code\":null,\"msg\":null,\"data\":";

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        LOG.info("Execute Fitler, start...");

        ResultWrapper wrapper = new ResultWrapper((HttpServletResponse)servletResponse);

        filterChain.doFilter(servletRequest, wrapper);
        byte[] content = wrapper.getContent();

        String str = "";
        if (content.length > 0) {
            str = new String(content, "UTF-8");
            LOG.info("Retrun value: {}", str);
        }

        StringBuffer buf = new StringBuffer(API_RESULT);
        buf.append(str);
        buf.append("}");

        ServletOutputStream out = servletResponse.getOutputStream();
        out.write(buf.toString().getBytes());
        out.flush();
        out.close();


        LOG.info("Execute Fitler, ...End");

    }
}

注册Filter

@Configuration
public class FilterConfig {

    @Bean
    public FilterRegistrationBean<ResultFilter> regResultFilter(){
        FilterRegistrationBean<ResultFilter> registrationBean
                = new FilterRegistrationBean<>();

        registrationBean.setFilter(new ResultFilter());
        registrationBean.addUrlPatterns("/todo/*");

        return registrationBean;
    }
}