依賴Spring的情況下，Java Web項目如何在啟動時加載數據庫中的數據？

原文：https://blog.csdn.net/u012345283/article/details/39558537

原文：https://blog.csdn.net/wandrong/article/details/44782627

我的嘗試：

1、繼承HttpServlet，在web.xml中配置servlet的<load-on-startup>1</load-on-startup>，項目啟動時globalParaService被注入了，但是跟蹤到init方法里面，globalParaService為null。（失敗）

public class InitSysServlet extends HttpServlet {

    private SysGlobalParaServiceI globalParaService;
    
    @Autowired
    public void setGlobalParaService(SysGlobalParaServiceI globalParaService) {
        this.globalParaService = globalParaService;
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        
        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
        
    }
}

然后，我試着手動創建globalParaService，代碼調整為

public class InitSysServlet extends HttpServlet {

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        
        SysGlobalParaServiceI globalParaService = new SysGlobalParaServiceImpl();
        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
        
    }
}

然而，SysGlobalParaServiceImpl里面依賴的其他由Spring注入的對象為null。

搞不定了，百度到以上兩篇文章，根據上面文章進行嘗試都成功了。

2、直接在init方法中獲取Spring的bean （成功）

首先在Spring配置文件中配置SysGlobalParaServiceImpl類對應的bean，然后在代碼中獲取，最終代碼如下：

public class InitSysServlet extends HttpServlet {

    private SysGlobalParaServiceI globalParaService;
    
    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        
        WebApplicationContext wac = ContextLoader.getCurrentWebApplicationContext();          
        globalParaService = (SysGlobalParaServiceI) wac.getBean("gpservice");

        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
    }
}

 

以下兩種則與servlet無關，而是繼承spring提供的接口。

3、實現Spring的接口InitializingBean，則實現類在被Sping初始化之后，會調用其中的afterPropertiesSet方法，代碼如下：

@Component
public class InitSysServlet implements InitializingBean {

    private SysGlobalParaServiceI globalParaService;
    
    @Autowired
    public void setGlobalParaService(SysGlobalParaServiceI globalParaService) {
        this.globalParaService = globalParaService;
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
    }


}

4、實現Spring的接口ApplicationListener<ContextRefreshedEvent>，在所有的bean初始化之后會調用其中的方法onApplicationEvent，代碼如下：

@Component
public class InitSysServlet implements ApplicationListener<ContextRefreshedEvent> {

    private SysGlobalParaServiceI globalParaService;
    
    @Autowired
    public void setGlobalParaService(SysGlobalParaServiceI globalParaService) {
        this.globalParaService = globalParaService;
    }

    @Override
    public void onApplicationEvent(ContextRefreshedEvent arg0) {
        SysGlobalPara codeRule = globalParaService.getCodeRule();
        if (null != codeRule) {
            SystemConfig.IS_SET_WIZADED = "true".equals(codeRule.getSysValue());
        } else {
            SystemConfig.IS_SET_WIZADED = false;
        }
    }

}

 

最后，我采用的是第4中，實現Spring的接口ApplicationListener<ContextRefreshedEvent>。