day02

使用过滤器来拦截用户请求，还需要在启动类上加上

@ServletComponentScan注解

/**
 * 检查用户是否已经完成登录
 * @author ccchai
 * @create 2022-06-24 11:02
 */
@Slf4j
@WebFilter(filterName = "loginCheckFilter",urlPatterns = "/*")
public class LoginCheckFilter implements Filter {
    //路径匹配器，支持通配符
    public static final AntPathMatcher PATH_MATCHER = new AntPathMatcher();

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        //1.获取本次请求的URI
        String requestURI = request.getRequestURI();
        log.info("本次请求的路径为{}",requestURI);

        //定义不需要处理的请求路径
        String[] urls = new String[]{
                "/employee/login",
                "/employee/logout",
                "/backend/**",
                "/front/**"
        };

        //2.判断本次请求是否需要处理
        boolean check = check(urls, requestURI);

        //3.如果不需要处理，则直接放行
        if (check){
            log.info("本次请求{}不需要处理",requestURI);
            filterChain.doFilter(request, response);
            return;
        }
        //4.判断登录状态，如果已登录，则直接放行
        if ((request.getSession().getAttribute("employee"))!=null){
            log.info("用户已登录，id为{}",request.getSession().getAttribute("employee"));
            filterChain.doFilter(request, response);
            return;
        }
        //5.如果未登录则返回未登录结果,通过输出流方式向客户端页面响应数据
        log.info("用户未登录");
        response.getWriter().write(JSON.toJSONString(R.error("NOTLOGIN")));
        return;

    }

    /**
     * 路径匹配，检查本次请求是否需要放行
     * @param urls
     * @param requestURI
     * @return
     */
    public boolean check(String[] urls,String requestURI){
        for (String url : urls) {
            boolean match = PATH_MATCHER.match(url, requestURI);
            if (match){
                return true;
            }
        }
        return false;
    }
}

定义全局异常类

@ControllerAdvice(annotations = {RestController.class, Controller.class})
@ResponseBody
@Slf4j
public class GlobalExceptionHandler {
    /**
     * 异常处理方法
     * @param ex
     * @return
     */
    @ExceptionHandler(SQLIntegrityConstraintViolationException.class)
    public R exceptionHandler(SQLIntegrityConstraintViolationException ex){
        log.error(ex.getMessage());
        if(ex.getMessage().contains("Duplicate entry")){
            String[] split = ex.getMessage().split(" ");
            return R.error(split[2]+"已存在");
        }
        return R.error("未知错误");
    }
}

分页查询

首先定义MP的配置类

/**
 * 配置MybatisPlus的分页插件
 * @author ccchai
 * @create 2022-06-24 17:08
 */
@Configuration
public class MyBatisPlusConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
        MybatisPlusInterceptor mybatisPlusInterceptor = new MybatisPlusInterceptor();
        mybatisPlusInterceptor.addInnerInterceptor(new PaginationInnerInterceptor());
        return mybatisPlusInterceptor;
    }
}

进行分页查询

/**
     * 员工信息分页查询
     * @param page
     * @param pageSize
     * @param name
     * @return
     */
    @GetMapping("/page")
    public R page(int page,int pageSize,String name){
        log.info("page = {},pageSize = {},name = {}",page,pageSize,name);

        //构造分页构造器
        Page pageInfo = new Page(page,pageSize);

        //构造条件构造器
        LambdaQueryWrapper queryWrapper = new LambdaQueryWrapper<>();

        //添加过滤条件
        queryWrapper.like(StringUtils.isNotEmpty(name), Employee::getName, name);

        //添加排序条件
        queryWrapper.orderByDesc(Employee::getUpdateTime);

        //执行查询
        employeeService.page(pageInfo, queryWrapper);
        return R.success(pageInfo);
    }

常见的问题：自动生成的id可能长度过长，导致js对long型数据进行处理时丢失精度，导致提交的id和数据库中的id不一致。

解决方法：我们可以在服务端给页面响应json数据时进行处理，将long型数据统一转为String字符串。

具体实现步骤：

1）提供对象转换器JacksonObjectMapper，基于Jackson进行Java对象到JSON数据的转换。

/**
 * 对象映射器:基于jackson将Java对象转为json，或者将json转为Java对象
 * 将JSON解析为Java对象的过程称为 [从JSON反序列化Java对象]
 * 从Java对象生成JSON的过程称为 [序列化Java对象到JSON]
 */
public class JacksonObjectMapper extends ObjectMapper {

    public static final String DEFAULT_DATE_FORMAT = "yyyy-MM-dd";
    public static final String DEFAULT_DATE_TIME_FORMAT = "yyyy-MM-dd HH:mm:ss";
    public static final String DEFAULT_TIME_FORMAT = "HH:mm:ss";

    public JacksonObjectMapper() {
        super();
        //收到未知属性时不报异常
        this.configure(FAIL_ON_UNKNOWN_PROPERTIES, false);

        //反序列化时，属性不存在的兼容处理
        this.getDeserializationConfig().withoutFeatures(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);


        SimpleModule simpleModule = new SimpleModule()
                .addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)))
                .addDeserializer(LocalDate.class, new LocalDateDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)))
                .addDeserializer(LocalTime.class, new LocalTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)))

                .addSerializer(BigInteger.class, ToStringSerializer.instance)
                .addSerializer(Long.class, ToStringSerializer.instance)
                .addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)))
                .addSerializer(LocalDate.class, new LocalDateSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_FORMAT)))
                .addSerializer(LocalTime.class, new LocalTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_TIME_FORMAT)));

        //注册功能模块 例如，可以添加自定义序列化器和反序列化器
        this.registerModule(simpleModule);
    }
}

2）在WebMvcConfig配置类中扩展Spring mvc的消息转换器，在此消息转换器中使用提供的对象转换器进行Java对象到JSON对象的转换

/**
     * 扩展MVC框架的消息转换器
     * @param converters
     */
    @Override
    protected void extendMessageConverters(List> converters) {
        log.info("扩展消息转换器...");
        //创建消息转换器对象
        MappingJackson2HttpMessageConverter messageConverter = new MappingJackson2HttpMessageConverter();
        //设置对象转换器，底层使用Jackson将Java对象转为JSON
        messageConverter.setObjectMapper(new JacksonObjectMapper());
        //将上面的消息转换器对象追加到MVC框架的转换器集合中
        converters.add(0,messageConverter);
    }