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背景：
我们经常会使用到比如数据库中的配置表信息，而我们不希望每次都去查询db，那么我们就想定时把db配置表的数据定时加载到flink的本地内存中，那么如何实现呢？
外部定时器定时加载实现
1.在open函数中进行定时器的创建和定时加载，这个方法对于所有的RichFunction富函数都适用,包括RichMap,RichFilter,RichSink等，代码如下所示
package wikiedits.schedule;import org.apache.flink.api.common.functions.RichFlatMapFunction;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.util.Collector;
import org.apache.flink.util.ExecutorUtils;import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;public class ScheduleRichMapFunction extends RichFlatMapFunction<String, String> {// 定时任务执行器private transient ScheduledExecutorService scheduledExecutorService;// 本地变量private int threshold;@Overridepublic void open(Configuration parameters) throws Exception {// 1.从db查询数据初始化本地变量
// threshold = DBManager.SELECTSQL.getConfig("threshold");// 2.使用定时任务更新本地内存的配置信息以及更新本地变量threshold的值scheduledExecutorService = Executors.newScheduledThreadPool(10);scheduledExecutorService.scheduleWithFixedDelay(() -> {// 2.1 定时任务更新本地内存配置项// List<ConfigEntity> configList = DBManager.SELECTSQL.getConfigs();
// for(ConfigEntity entity : configList){ConfigEntityLocalCache.getInstance().update("key", "value");
// }// 2.2 更新本地变量threshold的值
// threshold = DBManager.SELECTSQL.getConfig("threshold");}, 0, 100, TimeUnit.SECONDS);}@Overridepublic void flatMap(String value, Collector<String> out) throws Exception {}@Overridepublic void close() throws Exception {ExecutorUtils.gracefulShutdown(100, TimeUnit.SECONDS, scheduledExecutorService);}}//本地缓存实现
package wikiedits.schedule;import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;/*** 保存Config信息的本地缓存 ---定时同步DB配置表的数据*/
public class ConfigEntityLocalCache {private static volatile ConfigEntityLocalCache instance = new ConfigEntityLocalCache();/*** 获取本地缓存实例*/public static ConfigEntityLocalCache getInstance() {return instance;}/** 缓存内存配置项 */private static Cache<String, String> configCache =CacheBuilder.newBuilder().initialCapacity(50).maximumSize(500).build();/*** 更新本地缓存数据*/public boolean update(String key, String value){configCache.put(key, value);return true;}/*** 更新本地缓存数据*/public String getByKey(String key){return configCache.getIfPresent(key);}}2.在静态类中通过static语句块创建定时器并定时加载,代码如下
package wikiedits.schedule;import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;/*** 静态类定时加载DB配置表到本地内存中*/
public class StaticLoadUtil {// 定时任务执行器private static transient ScheduledExecutorService scheduledExecutorService;public static final Cache<String, String> configCache =CacheBuilder.newBuilder().initialCapacity(50).maximumSize(500).build();// 通过定时执行器定时同步本地缓存和DB配置表static {scheduledExecutorService = Executors.newScheduledThreadPool(10);scheduledExecutorService.scheduleWithFixedDelay(() -> {// 2.1 定时任务更新本地内存配置项// List<ConfigEntity> configList = DBManager.SELECTSQL.getConfigs();// for(ConfigEntity entity : configList){configCache.put("key", "value");// }// 2.2 更新本地变量threshold的值// threshold = DBManager.SELECTSQL.getConfig("threshold");}, 0, 100, TimeUnit.SECONDS);}/*** 获取本地缓存*/public static Cache<String, String> getConfigCache() {return configCache;}}总结：
1.外部定时器可以通过在富函数的open中进行初始化并开始定时执行
2.外部定时器也可以通过创建一个单独的静态类，然后在static模块中进行初始化并开始定时执行