问题背景

最近在使用Berkeley DB 持久化一个实体类，这个实体类中有个字段是java.sql.TimeStamp类型

然后程序运行就出现了如下错误：

Class could not be loaded or is not persistent: java.sql.Timestamp

故障分析

出现这个错误是因为Berkeley DB 里面也有一个Timestamp类型，这个类型 和java.sql.Timestamp 字段出现了不兼容故障。

解决思路是设计一个代理类来解决。

故障解除

1. 设计一个代理类

import com.sleepycat.persist.model.Persistent;
import com.sleepycat.persist.model.PersistentProxy;

import java.sql.Timestamp;

/**
 * 功能:
 * 作者: 星云
 * 时间: 2019/9/6 14:20
 */
@Persistent(proxyFor = Timestamp.class)
public class ProxyForTimeStamp implements PersistentProxy<Timestamp> {

    Timestamp timestamp;
    @Override
    public void initializeProxy(Timestamp timestamp) {
        this.timestamp=timestamp;
    }

    @Override
    public Timestamp convertProxy() {
        return this.timestamp;
    }
}

2.然后在环境配置中加载这个代理类

  EntityModel entityModel=new AnnotationModel();
  entityModel.registerClass(ProxyForTimeStamp.class);
  myStoreConfig.setModel(entityModel);

完整代码如下：

import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.Environment;
import com.sleepycat.je.EnvironmentConfig;
import com.sleepycat.persist.EntityStore;
import com.sleepycat.persist.StoreConfig;
import com.sleepycat.persist.model.AnnotationModel;
import com.sleepycat.persist.model.EntityModel;
import com.xingyun.berkeleydb.ProxyForTimeStamp;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;

/**
 * 功能: Berkeley Database Java Edition 环境管理器
 * 作者: 星云
 * 时间: 2019/9/6 9:15
 */
@SuppressWarnings("unused")
public final class BDBEnvironmentManager {
    //禁用构造方法
    private BDBEnvironmentManager() {}

    private final static Logger LOGGER = LoggerFactory.getLogger(BDBEnvironmentManager.class);

    private static volatile BDBEnvironmentManager bdbEnvironmentManager = null;

    // 数据库环境对象
    private static Environment myEnvironment = null;
    // 数据存储基本单元
    private static EntityStore myEntityStore = null;

    /**
     * @return
     */
    public static Environment getMyEnvironment() {
        if (myEnvironment != null) {
            return myEnvironment;
        } else {
            return null;
        }
    }

    /**
     * @return
     */
    public static EntityStore getMyEntityStore() {
        if (myEntityStore != null) {
            return myEntityStore;
        } else {
            return null;
        }
    }

    // 懒汉式

    /**
     * @param envHome
     * @param readOnly
     * @return
     */
    public static BDBEnvironmentManager getInstance(File envHome, Boolean readOnly) {

        if (envHome == null) {
            return null;
        }
        if (bdbEnvironmentManager == null) {
            // 添加同步锁,会更安全高效
            synchronized (BDBEnvironmentManager.class) {
                if (bdbEnvironmentManager == null) {

                    // 代码在这里执行确保应用程序中只有一个实例
                    bdbEnvironmentManager = new BDBEnvironmentManager();
                    // 创建一个BDB 环境配置对象
                    EnvironmentConfig myEnvConfig = new EnvironmentConfig();
                    // 创建一个数据存储配置对象
                    StoreConfig myStoreConfig = new StoreConfig();

                    if (readOnly == null) {
                        readOnly = false;
                    }

                    EntityModel entityModel=new AnnotationModel();
                    entityModel.registerClass(ProxyForTimeStamp.class);
                    myStoreConfig.setModel(entityModel);

                    // 设置该环境是否为只读,true 为只读，false 为可读写
                    myEnvConfig.setReadOnly(readOnly);
                    // 设置数据存储配置是否为只读,true 为只读，false 为可读写
                    myStoreConfig.setReadOnly(readOnly);

                    // 如果该环境不存在是否重建，true 允许重建，false 不可重建
                    myEnvConfig.setAllowCreate(!readOnly);
                    // 如果该存储配置不存在是否重建，true 允许重建，false 不可重建
                    myStoreConfig.setAllowCreate(!readOnly);

                    //数据库环境是否支持事务
                    myEnvConfig.setTransactional(!readOnly);
                    //存储环境是否支持事务
                    myStoreConfig.setTransactional(!readOnly);


                    // 如果文件不存在则创建
                    if (!envHome.exists()) {
                        try {
                            envHome.mkdir();
                        } catch (Exception e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }

                    // 打开 environment 和 entity store
                    if (myEnvironment == null || myEntityStore == null) {
                        try {
                            myEnvironment = new Environment(envHome, myEnvConfig);
                            myEntityStore = new EntityStore(myEnvironment, "EntityStore", myStoreConfig);
                        } catch (DatabaseException e) {
                            LOGGER.error("Database Exception",e);
                        }
                    }
                }
            }
        }
        return bdbEnvironmentManager;
    }

    // Close the store and environment.

    /**
     * Close the store and environment
     */
    public static void close() {
        // 判断存储对象是否为空
        if (myEntityStore != null) {
            try {
                // 尝试关闭存储对象
                myEntityStore.close();
            } catch (DatabaseException dbe) {
                LOGGER.error("Error closing store: " + dbe.toString());
            }
        }
        // 判断环境是否为空
        if (myEnvironment != null) {
            try {
                // 关闭环境
                myEnvironment.close();
            } catch (DatabaseException dbe) {
                LOGGER.error("Error DatabaseException: " + dbe.toString());
            }
        }
    }
}

参考资料：

• Getting an exception when trying to persist Pattern object from java.util.regex package ( using Berkeley DB Java）