Java面试知识总结三

1.SpringMVC在项目中的应用？

1）service层，项目的业务逻辑层，一般先定义一个接口，在写一个实现类，实现所有的接口方法。service的实现类中要加注解@Service(用于标注业务层组件),@Resource 注入dao组件，方便在业务层中调用对用dao的方法.

@Service
public class ContentServiceImpl implements ContentService{
 
 @Autowired
 private   ContentDao  contentdao;
 

2）controller层，控制层它把用户请求的数据经过业务处理层处理之后封装成一个Model ，然后再把该Model 返回给对应的View 进行展示。controller要添加注解@Controller（用于标注控制层组件）),@Resource 注入service组件，方便调用业务层的方法.

@Controller
public class ContentController {
 @Autowired
 private ContentService contentService;
 
 //用户评论 提交 按钮--insert
 @RequestMapping("/ContentController")
    @ResponseBody
    public Object  addByText( @ModelAttribute("content")  Content content,HttpServletRequest request){    
     content.setUsername(((User)(request.getSession().getAttribute("sessionuser"))).getUsername());
     contentService.addByText(content);
       return new Gson().toJson(contentService.queryOneForJustNow());
      }

2.Redis缓存数据存放的时间？

列：在实现积分项目业务中，对不同场景设置了不同的key-value缓存到了redis中。但是因为对不同业务的key需要缓存的时间不尽相同，这里自定义工具类来实现。 
设置redis缓存key，截取部分代码：

 

  try{
  //cacheManager就相当从redis链接池获取一个连接，具体工厂类获取在后面备注
  cacheManager = (RedisCacheManager) CacheManagerFactory.getCacheManager();
  totalMonCount = Float.parseFloat(cacheManager.getString(monthKey)) + centCount;
  if (centLimitByMonth != -1){
      if (totalMonCount > centLimitByMonth) {
           // 超出月上限不再累计
           logger.error("exceeds the month limit cents! [" + totalMonCount + "]   code:[" + code + "]");
           return null;
      }
}

//当未超出月额度，此时要对日额度进行判断；只需判断其是否超出日上限积分
if (dayKey != null){
    //累积积分;因为签到其实是没有每日积分的，是按次数规则累积的；但为了统一，直接用centCount代替（都是签一次1分）
    totalDayCount = Float.parseFloat(cacheManager.getString(dayKey)) + centCount;
    if (centLimitByDay != -1){
          if (totalDayCount > centLimitByDay){
            logger.info("[ERROR]teacher everyday assign cents > month limit! total:  ["+totalDayCount+"]");
           return null;
         }
     }
      cacheManager.set(dayKey,totalDayCount.toString(),DateUtil.getSecsToEndOfCurrentDay());

}
//对月限制key进行积分累加
//每月1号凌晨1点启动脚本删除，同时设置了保存到月底缓存时间双重保障
cacheManager.set(monthKey, totalMonCount.toString(), DateUtil.getSecsToEndOfCurrentDay());
logger.info("==monthkey:"+monthKey+"---value:"+totalMonCount);
 }
                            ...
}catch(Exception e){
                    logger.error("===cache redis fail!");
                    e.printStackTrace();

            }finally {

                    if (cacheManager != null){
                            cacheManager.close();
                    }
            }





//工厂类获取redis链接
public class CacheManagerFactory {

    private static ICacheManager cacheManager;

    private CacheManagerFactory(){
    };

    public static ICacheManager getCacheManager(){
        if(cacheManager == null){
            synchronized (CacheManagerFactory.class) {
                if(cacheManager == null){
                    JedisPooler jedisPooler = RedisPoolerFactory.getJedisPooler();
                    cacheManager = new RedisCacheManager(jedisPooler);
                }
            }
        }
        return cacheManager;
    }

}

//redis链接池工厂类获取链接
public class RedisPoolerFactory {

    private static JedisPooler jedisPooler; 

    private RedisPoolerFactory(){
    };

    public static JedisPooler getJedisPooler(){
        if(jedisPooler == null){
            synchronized (RedisPoolerFactory.class) {
                if(jedisPooler == null){
                    jedisPooler = new JedisPooler();
                }
            }
        }
        return jedisPooler;
    }

}


/**
 * 
 * Redis 连接池实例
 * 
 * @author Ethan.Lam
 * @createTime 2011-12-3
 * 
 */
public class JedisPooler {

    private JedisPool pool;
    private String REDIS_HOST;
    private String REDIS_PSW;
    private int REDIS_PORT;
    private int REDIS_MaxActive;
    private int REDIS_MaxIdle;
    private int REDIS_MaxWait;

    public JedisPooler(String config) {
        __init(config);
    }

    public JedisPooler() {
        __init("/jedisPool.properties");
    }

    private void __init(String conf) {
        // 完成初始化工作
        Properties prop = new Properties();
        try {
            InputStream _file = loadConfig(conf);
            prop.load(_file);
            REDIS_HOST = prop.getProperty("REDIS.HOST");
            REDIS_PSW = prop.getProperty("REDIS.PSW");
            REDIS_PORT = Integer.parseInt(prop.getProperty("REDIS.PORT").trim());
            REDIS_MaxActive = Integer.parseInt(prop.getProperty("REDIS.MaxActive").trim());
            REDIS_MaxIdle = Integer.parseInt(prop.getProperty("REDIS.MaxIdle").trim());
            REDIS_MaxWait = Integer.parseInt(prop.getProperty("REDIS.MaxWait").trim());
        } catch (Exception e) {
            e.printStackTrace();
            REDIS_HOST = "localhost";
            throw new NullPointerException(conf + " is not found !");
        }
        JedisPoolConfig config = new JedisPoolConfig();
        config.setMaxActive(REDIS_MaxActive);
        config.setMaxIdle(REDIS_MaxIdle);
        config.setMaxWait(REDIS_MaxWait);
        config.setTestOnBorrow(true);
        System.out.println("REDIS Cache服务信息:  当前连接的服务IP为：" + REDIS_HOST + ":" + REDIS_PORT);
        if (null == REDIS_PSW || "".equals(REDIS_PSW.trim())){
            pool = new JedisPool(config, REDIS_HOST, REDIS_PORT, 5000);
        }
        else{
            pool = new JedisPool(config, REDIS_HOST, REDIS_PORT, 5000, REDIS_PSW);
        }

    }

    public Jedis getJedis() {
        return pool.getResource();
    }

    public void returnResource(Jedis jedis) {
        pool.returnResource(jedis);
    }

    public JedisPool getPool() {
        return pool;
    }

    InputStream loadConfig(String configPath) throws Exception {
        InputStream _file = null;
        try {
            String file = JedisPooler.class.getResource(configPath).getFile();
            file = URLDecoder.decode(file);
            _file = new FileInputStream(file);
        } catch (Exception e) {
            System.out.println("读取jar中的配置文件....");
            String currentJarPath = URLDecoder.decode(JedisPooler.class.getProtectionDomain()
                    .getCodeSource().getLocation().getFile(), "UTF-8"); // 获取当前Jar文件名
            System.out.println("currentJarPath：" + currentJarPath);
            java.util.jar.JarFile currentJar = new java.util.jar.JarFile(currentJarPath);
            java.util.jar.JarEntry dbEntry = currentJar.getJarEntry("jedisPool.properties");
            InputStream in = currentJar.getInputStream(dbEntry);
            _file = in;
        }
        return _file;
    }

}

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