    return em.createQuery(sql 語(yǔ)句).setLockMode(LockModeType.NONE).getResultList();
    //分解寫法大概是:
    Query query = getSession().createQuery(hql);
    query.setLockMode(LockModeType.NONE);

EntityManager 是一個(gè)輔助類,createQuery后返回的就是一個(gè)Query對(duì)象,然后通過

setLockMode設(shè)置鎖的級(jí)別即可.

LockModeType 類型	解釋
LockMode.READ	事務(wù)的隔離級(jí)別是Repeatable Read或Serializable時(shí)，請(qǐng)求讀取數(shù)據(jù)庫(kù)記錄時(shí)自動(dòng)獲得
LockMode.WRITE	請(qǐng)求插入或更新數(shù)據(jù)庫(kù)記錄時(shí)自動(dòng)獲得
LockMode.OPTIMISTIC	樂觀鎖
LockMode.OPTIMISTIC_FORCE_INCREMENT	樂觀鎖,通過version控制
LockMode.PESSIMISTIC_READ	與LockMode.PESSIMISTIC_WRITE相同
LockMode.PESSIMISTIC_WRITE	事務(wù)開始即獲得數(shù)據(jù)庫(kù)的鎖
LockMode.PESSIMISTIC_FORCE_INCREMENT	事務(wù)開始即設(shè)置version
LockMode.NONE	取消任何鎖，如事務(wù)結(jié)束后的所有對(duì)象，或執(zhí)行了Session的update()、

二樂觀鎖的詳細(xì)用法

樂觀鎖本篇的主要內(nèi)容

實(shí)體類是關(guān)鍵 , 樂觀鎖常用方法是通過version來控制 ,

數(shù)據(jù)庫(kù)對(duì)應(yīng)的表中需要有一個(gè)字段(名字隨意),字段類型設(shè)置成BigInt即可
業(yè)務(wù)不對(duì)該字段進(jìn)行控制,字段的控制交由系統(tǒng)處理
每一次修改都會(huì)導(dǎo)致version遞增
當(dāng)出現(xiàn)同時(shí)獲得該記錄的對(duì)象且均需要修改時(shí),當(dāng)?shù)谝粋€(gè)已經(jīng)提交事務(wù),version字段發(fā)生改變,后面提交的事務(wù)發(fā)現(xiàn)version版本不對(duì),則無法提交,拋出異常

實(shí)體類(注意其中的@Version注解)

@Entity
public class User {
    @Id
    @GeneratedValue
    private Long id;
    private String username;
    private String userdesc;
    @Version
    private Long version;
    public User() {
    }
    public User(String username, String userdesc) {
        this.username = username;
        this.userdesc = userdesc;
    }
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getUserDesc() {
        return userdesc;
    }
    public void setUserDesc(String userdesc) {
        this.userdesc = userdesc;
    }
    public Long getVersion() {
        return version;
    }
    public void setVersion(Long version) {
        this.version = version;
    }
}

controller中通過sleep將線程沉睡,測(cè)試事務(wù)的提交性

@RestController
public class UserController {
    private Logger logger = LoggerFactory.getLogger(getClass());
    @Autowired
    UserService userService;
    @PostMapping("/changeone")
    @Transactional
    public String changeone() {
        User user = userService.findUser("gang");
        try {
            logger.info("修改1 before:user--{}--Versdion:{}", user.getUserDesc(), user.getVersion());
            Thread.sleep(25000);
            user.setUserDesc("修改1");
            logger.info("修改1 :user--{}--version:{}", user.getUserDesc(), user.getVersion());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (Exception e) {
            logger.info("eeeeeeeeeeeeee");
            e.printStackTrace();
        }
        return "true";
    }
    @PostMapping("/changetwo")
    @Transactional
    public String changetwo() {
        User user = userService.findUser("gang");
        try {
            logger.info("修改2 before:user--{}--version:{}", user.getUserDesc(), user.getVersion());
            Thread.sleep(30000);
            user.setUserDesc("修改2");
            logger.info("修改2:user--{}--version:{}", user.getUserDesc(), user.getVersion());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (Exception e) {
            logger.info("eeeeeeeeeeeeee");
            e.printStackTrace();
        }
        return "true";
    }
    @PostMapping("/changethree")
    @Transactional
    public String changethree() {
        User user = userService.findUser("gang");
        logger.info("修改3 before:user--{}--version:{}", user.getUserDesc(), user.getVersion());
        user.setUserDesc("修改3");
        logger.info("修改3 :user--{}--version:{}", user.getUserDesc(), user.getVersion());
        return "true";
    }
    @PostMapping("/newuser")
    @Transactional
    public String newuser() {
        logger.info("save user");
        User user = new User();
        user.setUserDesc("第一次創(chuàng)建");
        user.setUsername("gang");
        userService.saveUser(user);
        return "true";
    }
}

以及service及repository

@Service
public class UserService {
    @Autowired
    UserRepository userRepository;
    public User findUser(String username){
        return userRepository.findByUsername(username);
    }
    public void saveUser(User user){
        userRepository.save(user);
    }
}
UserRepository 
public interface UserRepository extends JpaRepository<User,Long> {
    User findByUsername(String username);
}

總結(jié)

使用很簡(jiǎn)單,version是自動(dòng)增長(zhǎng)的,唯一的缺點(diǎn)是拋出的異常不易捕獲,捕獲的方法:

    @Resource
    private UserTransaction rtc;
     try {
            rtc.begin();
            User user = userService.findUser("gang");
            user .setDesc("異常捕獲");
             rtc.commit();
        } catch (OptimisticLockException e) {
            throw new OptimisticLockException ();
        } catch (Exception e) {
            throw new Exception ();
        }

注意其中的 rtc.begin(); 以及 rtc.commit();

不同于@Transaction,這種是手動(dòng)的提交方法

以上為個(gè)人經(jīng)驗(yàn)，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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