并行请求的NullPointer异常

Question

有人能告诉我这段代码出了什么问题吗？

我得到空指针异常，我假设是因为有多个请求

@Service
public class GernericMockingServiceImpl implements GenericMockingService {

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

    @Override
    public String getJsonResponse(GenericMockingForm genericMockingForm, String requestURI) throws Exception {
        LOG.info("printing requestURI : "+requestURI);
        String path = new URI(requestURI).getPath();
        //resolves to a folder name in src/main/resources
        String folderName = path.substring(path.lastIndexOf('/') + 1);
        LOG.info("printing folderName : " + folderName);
        String jsonResponse = null;
        StringBuilder sb = new StringBuilder();

        //check if the request body has prodcut id's which means that the request is for products else check for sku's which means that the request is for price or stock
        if(!Objects.isNull(genericMockingForm.getProductIds()) && !genericMockingForm.getProductIds().isEmpty()){
            //currently it iterates over all the product id's/sku's in the request and appends the content of all the id's
            //TODO: the content of the file is not exactly how we want it to be for multiple ids' But for the single id it just works.
            // TODO: Needs to be refactored later when we handle multiple id's in request
            for(String productId : genericMockingForm.getProductIds()){
                jsonResponse = getJson(folderName, productId, sb);
            }
        }else{
            for (String sku : genericMockingForm.getSkus()) {
                jsonResponse = getJson(folderName, sku, sb);
            }
        }
        LOG.info("printing jsonResponse : " + jsonResponse);
        return jsonResponse;
    }

    private String getJson(String folderName, String id, StringBuilder sb) throws Exception {
        String responseJson = null;
        String filePath = "data" + File.separator + folderName + File.separator + id + ".json";
        LOG.info("printing filePath : " + filePath);
        LOG.info("printing id : " + id);
        File f = new File(filePath);
        if(f.exists()){
            try (InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(filePath)) {
                LOG.info("printing inputStream : " + inputStream);
                if (inputStream != null) {
                    responseJson = IOUtils.toString(inputStream, StandardCharsets.UTF_8.name());
                }
                if (responseJson == null || responseJson.isEmpty()) {
                    LOG.info("json response is null : ");
                    throw new JsonNotFoundException(Constant.JSON_NOT_FOUND);   
                }
                sb.append(responseJson);
            } catch (IOException e) {
                LOG.info("IO exception : ");
                throw new IOException(e);
            } catch (Exception e) {
                LOG.info(" exception : ");
                throw new Exception(e);
            }
        }
        else{
            LOG.info("file doesnt exists : " + filePath);
        }
        return sb.toString();
    }
}

**我有3个并行请求访问包含3个不同文件的文件夹，并尝试读取这些文件

这是我的堆栈跟踪**

  2019-03-05 17:30:29.335  INFO 82 --- [nio-8080-exec-1] c.k.m.controller.ProductController       : Received request for Mocking Controller
    2019-03-05 17:30:29.335  INFO 82 --- [nio-8080-exec-3] c.k.m.controller.ProductController       : Received request for Mocking Controller
    2019-03-05 17:30:29.335  INFO 82 --- [nio-8080-exec-2] c.k.m.controller.ProductController       : Received request for Mocking Controller
    2019-03-05 17:30:29.336  INFO 82 --- [nio-8080-exec-2] c.k.m.s.impl.GernericMockingServiceImpl  : printing requestURI : /mocking/api/stocks
    2019-03-05 17:30:29.336  INFO 82 --- [nio-8080-exec-3] c.k.m.s.impl.GernericMockingServiceImpl  : printing requestURI : /mocking/get-products
    2019-03-05 17:30:29.337  INFO 82 --- [nio-8080-exec-3] c.k.m.s.impl.GernericMockingServiceImpl  : printing folderName : get-products
    2019-03-05 17:30:29.338  INFO 82 --- [nio-8080-exec-3] c.k.m.s.impl.GernericMockingServiceImpl  : printing filePath : data/get-products/1610-17637-319.json
    2019-03-05 17:30:29.338  INFO 82 --- [nio-8080-exec-3] c.k.m.s.impl.GernericMockingServiceImpl  : printing id : 1610-17637-319
    2019-03-05 17:30:29.338  INFO 82 --- [nio-8080-exec-3] c.k.m.s.impl.GernericMockingServiceImpl  : file doesnt exists : data/get-products/1610-17637-319.json
    2019-03-05 17:30:29.338  INFO 82 --- [nio-8080-exec-3] c.k.m.s.impl.GernericMockingServiceImpl  : printing jsonResponse : 
    2019-03-05 17:30:29.336  INFO 82 --- [nio-8080-exec-1] c.k.m.s.impl.GernericMockingServiceImpl  : printing requestURI : /mocking/api/prices
    2019-03-05 17:30:29.338  INFO 82 --- [nio-8080-exec-1] c.k.m.s.impl.GernericMockingServiceImpl  : printing folderName : prices
    2019-03-05 17:30:29.337  INFO 82 --- [nio-8080-exec-2] c.k.m.s.impl.GernericMockingServiceImpl  : printing folderName : stocks
    2019-03-05 17:30:29.343  INFO 82 --- [nio-8080-exec-2] c.k.m.s.impl.GernericMockingServiceImpl  : printing filePath : data/stocks/1610-17637.json
    2019-03-05 17:30:29.343  INFO 82 --- [nio-8080-exec-2] c.k.m.s.impl.GernericMockingServiceImpl  : printing id : 1610-17637
    2019-03-05 17:30:29.343  INFO 82 --- [nio-8080-exec-2] c.k.m.s.impl.GernericMockingServiceImpl  : file doesnt exists : data/stocks/1610-17637.json
    2019-03-05 17:30:29.343  INFO 82 --- [nio-8080-exec-2] c.k.m.s.impl.GernericMockingServiceImpl  : printing jsonResponse : 
    2019-03-05 17:30:29.354 ERROR 82 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

    java.lang.NullPointerException: null
        at com.kfz24.mockingservice.service.impl.GernericMockingServiceImpl.getJsonResponse(GernericMockingServiceImpl.java:45) ~[classes/:na]
        at com.kfz24.mockingservice.controller.GenericMockingController.processRequest(GenericMockingController.java:32) ~[classes/:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
        at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
        **at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]**

Answer 1

我得到null指针异常，我假设是因为有多个请求

我认为你的假设是错误的。

注释中的

：空值为此行for (String sku : genericMockingForm.getSkus()) {

这似乎表明genericMockingForm.getSkus()正在返回null，因为这里使用的唯一另一个对象是上面测试过的genericMockingForm。

您应该在该表单测试上进行相同的null检查：

 if (!Objects.isNull(genericMockingForm.getSkus())) ...

如果它们都是null，那么你应该说出某种用法错误。