通过new方式得到的普通类获取spring的bean对象

╰半橙微兮° 2022-05-13 08:28 533阅读 0赞

在Spring框架中，我们通常将bean对象交给spring容器，然后使用注解的方式引入，不用手动的去创建类。

如在service类上加@Service，在controller类上加@Controller，通过@Autowired注解引入调用bean对象的方法

service类：

public interface ISupplierService { 
        public SupplierBase getSupplier(Long id);
    }
    
    
    @Service
    public class SupplierServiceImpl implements ISupplierService { 
        @Autowired  
        private ISupplierDao supplierDao; 
    
        @Override
        public SupplierBase getSupplier(Long id) {
            return supplierDao.getSupplier(id);
        }
    }

controller类：

@Controller
    @RequestMapping(value="/supplier")
    public class SupplierManagementAction{ 
        @Autowired
        private ISupplierService service;
    
        @RequestMapping(value="/supplierIndex") 
        public String supplierIndex(ModelMap modelMap, Long supplierId) throws Exception{
            if(null!=id && id.trim().length()>0 ){
                SupplierBase supplierBase = service.getSupplierByRegionType(supplierId);
                if(null!=supplierBase){
                    modelMap.put("supplierBase", supplierBase);
                }
            }
            return "supplier/supplierIndex";
        }
    }

但是，最近在项目中遇到这种情况：  
导出excel数据，首先根据条件查询符合要求的数据，然后在Controller中使用new的方式得到普通类，最后将数据传到普通类中，专门处理excel构建。部分代码如下：

controller类：

@Controller
    @RequestMapping(value="/sproduct")
    public class SupplierProductManagementAction{ 
    
        @RequestMapping(value="/exportExcel", method=RequestMethod.POST) 
        public ModelAndView exportExcel(@ModelAttribute PmSupplierBase productFromBean,ModelMap model,HttpSession session) {
            int pageIndex = 1;
            if(null!=productFromBean.getBatchNum()){
                pageIndex = productFromBean.getBatchNum().intValue();
            }
            productFromBean.setBusinessType(super.getBusinessType());
            productFromBean.setExportExcel(true);
            Page<PmSupplierBase> supplierList = productService.queryPmSupplierProduct(productFromBean, excelMaxHang, pageIndex,getBty());
    
            SProductExportExcel productExcel = new SProductExportExcel();
    
            return new ModelAndView(productExcel,"pmData",supplierList.getResults());
        }
    }

用于处理生成excel的普通类：

public class SProductExportExcel extends AbstractExcelView { 
    
        @Override
        protected void buildExcelDocument(Map<String, Object> model,
                HSSFWorkbook workbook, HttpServletRequest request,
                HttpServletResponse response) throws Exception {
            Date currDate = new Date();
            HSSFSheet sheet = workbook.createSheet("PSupplier导出(" + DateUtils.dateFormatToString(currDate, "yyyy-MM-dd") + ")");    
            HSSFRow sheetRow = sheet.createRow(0); 
            int index = 0;
            HSSFCellStyle colorStyle = workbook.createCellStyle();
            colorStyle.setFillForegroundColor(HSSFColor.YELLOW.index);
            colorStyle.setFillBackgroundColor(HSSFColor.YELLOW.index);
            colorStyle.setFillPattern(HSSFColor.YELLOW.index);
            HSSFCell cell = sheetRow.createCell(index++);
            cell.setCellStyle(colorStyle);
            cell.setCellValue("产品编码");
    
            cell = sheetRow.createCell(index++);
            cell.setCellStyle(colorStyle);
            cell.setCellValue("产品名称");
    
            @SuppressWarnings("unchecked")
            List<PmSupplierBase> dataList = (List<PmSupplierBase>)model.get("pmData");
            int num = null==dataList?0:dataList.size();
    
            List<CommonTypeBase> noPrList = null;
            if(num >= 1){
                noPrList = (List<CommonTypeBase>)dataList.get(0).getNoPurchaseReasonList();
            }
            String[] noPrArray = StringUtil.ListToArray(noPrList, "typeName");
            Map<String,String> noPrMap = (Map<String,String>)StringUtil.ListToMap(noPrList, "typeValue", "typeName");
    
            DVConstraint noPrConstraint = DVConstraint.createExplicitListConstraint(noPrArray);
            //四个参数分别是：起始行、终止行、起始列、终止列 
            CellRangeAddressList noPrRegions = new CellRangeAddressList(1,num,30,30);
            //数据有效性对象 
            HSSFDataValidation noPrDataValidation = new HSSFDataValidation(noPrRegions, noPrConstraint);
            sheet.addValidationData(noPrDataValidation);
    
            PmSupplierBase base = null;
            for (int i = 0; i < num; i++) {
                base = dataList.get(i);
                sheetRow = sheet.createRow(i+1); 
                if(null==base)
                    continue;
                index = 0;
                sheetRow.createCell(index++).setCellValue(null==base.getProductNo()?"":base.getProductNo());
                sheetRow.createCell(index++).setCellValue(null==base.getSupplierProductName()?"":base.getSupplierProductName());
            }    
            String filename = "PSupplier" + DateUtils.dateFormatToString(currDate, "yyyyMMddHHmmss") + ".xls";//设置下载时客户端Excel的名称 
            OutputStream ouputStream = null;
            try {
                filename = HelpUtil.encodeFilename(filename, request);//处理中文文件名 
                response.setContentType("application/vnd.ms-excel");     
                response.setHeader("Content-disposition", "attachment;filename=" + filename);     
                ouputStream = response.getOutputStream();     
                workbook.write(ouputStream);     
                ouputStream.flush();  
            } catch (Exception e) {
                e.printStackTrace();
            }finally{
                if(null!=ouputStream){
                    ouputStream.close();
                }
            }
        }
    }

现在excel中有一列数据需要调用service类中的方法查询将结果展示，然后同事A就直接在SProductExportExcel 类中通过注解直接引入

public class SProductExportExcel extends AbstractExcelView { 
    
        /**同事A添加的*/
        @Autowired
        IMerwareConstantService merwareConstantService;
    
        @Override
        protected void buildExcelDocument(Map<String, Object> model,
                HSSFWorkbook workbook, HttpServletRequest request,
                HttpServletResponse response) throws Exception {
                    //....
                    //....
                    //同事A添加的一行代码
                    String merchantName = merwareConstantService.getMNameByMId(base.getMerchantId());
                }
        }

结果我拉取代码测试导出，后台直接报错：java.lang.NullPointException

最开始怀疑是数据的问题，在获取数据计算的时候未判断空导致的这个异常，但是debug发现是  
merwareConstantService.getMNameByMId(base.getMerchantId());  
这行代码merwareConstantService为空导致的。

**分析代码:**

如果想用@autowired，那么这个类本身也应该是在spring的管理下，即SProductExportExcel 也要标注为一个component（或Service），这样spring才知道要注入依赖。

而在controller中通过new的方式获取的SProductExportExcel，并没有交给spring管理，通过注解引入方式获取不到spring的bean对象

那么问题的关键就在于获取merwareConstantService的方式。

而获取spring的bean对象，还可以通过ApplicationContext.getBean()。

**解决方案如下：**

创建一个工具类，用于获取bean对象

public class SpringContextUtil implements ApplicationContextAware { 
        private static ApplicationContext applicationContext = null;
    
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            this.applicationContext = applicationContext;
        }
    
        public static ApplicationContext  getApplicationContext(){
            return applicationContext;
        }
    
        /** * 适用于springbean使用注解@Service("XXXService") * 获取接口对象 参数传入 XXXService * @param beanName * @return */
        public static Object getBean(String beanName){
            return applicationContext.getBean(beanName);
        }
    
        /** * 适用于springbean使用注解@Service * 获取接口对象 参数传入 XXXService.class 不是 XXXServiceImpl.class * @param c * @return */
        public static Object getBean(Class c){
            return applicationContext.getBean(c);
        }
    }

然后将此bean加到spring容器中，applicationContext.xml中添加：

在SProductExportExcel中就通过这个工具类获取service：

public class SProductExportExcel extends AbstractExcelView { 
    
        /**同事A添加的*/
        //@Autowired
        //IMerwareConstantService merwareConstantService;
    
        @Override
        protected void buildExcelDocument(Map<String, Object> model,
                HSSFWorkbook workbook, HttpServletRequest request,
                HttpServletResponse response) throws Exception {
    
                    //更改新的获取方式
                    ApplicationContext context = SpringContextUtil.getApplicationContext();
                    IMerwareConstantService merwareConstantService = (IMerwareConstantService)context.getBean(IMerwareConstantService.class);
                    //....
                    //....
                    //同事A添加的一行代码
                    String merchantName = merwareConstantService.getMNameByMId(base.getMerchantId());
                }
        }

再次测试导出，成功。

**有一点要注意下：**  
IMerwareConstantService merwareConstantService = (IMerwareConstantService)context.getBean(IMerwareConstantService.class);

刚开始我传入的是类名  
context.getBean(“IMerwareConstantService”);

仍然获取不到service，网上查资料发现getBean()具体传入”类名”还是 类名.class是有区别的，要根据自己的service的注解来定。

如：  
@Service  
public class MerwareConstantServiceImpl implements IMerwareConstantService\{\}  
那么context.getBean()传入类名.class

@Service(“IMerwareConstantService”)  
public class MerwareConstantServiceImpl implements IMerwareConstantService\{\}  
那么context.getBean()传入类名