<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-mongodb</artifactId>
</dependency>

spring.data.mongodb.uri=mongodb://localhost:27017,localhost:27018,localhost:27019/mydatabase?replicaSet=rs0
# 或者對于分片集群，連接到 mongos 實(shí)例
# spring.data.mongodb.uri=mongodb://mongos1:27017,mongos2:27017/mydatabase

import com.mongodb.client.MongoClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.mongodb.MongoDatabaseFactory;
import org.springframework.data.mongodb.MongoTransactionManager;
import org.springframework.data.mongodb.core.MongoTemplate; // 僅為示例，非必需

@Configuration
public class MongoConfig {

    // Spring Boot 會自動配置 MongoDatabaseFactory
    // 你只需要注入它來創(chuàng)建 MongoTransactionManager
    @Bean
    MongoTransactionManager transactionManager(MongoDatabaseFactory dbFactory) {
        return new MongoTransactionManager(dbFactory);
    }

    // 可選: 如果你也想配置一個 MongoTemplate bean
    // @Bean
    // public MongoTemplate mongoTemplate(MongoDatabaseFactory dbFactory, MongoClient mongoClient) {
    //     return new MongoTemplate(mongoClient, dbFactory.getMongoDatabase().getName());
    // }
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional; // Spring的事務(wù)注解
import com.mongodb.MongoException; // 更通用的MongoDB異常
import com.mongodb.MongoTransactionException; // 事務(wù)特定異常

@Service
public class AccountService {

    @Autowired
    private AccountRepository accountRepository; // 假設(shè)你有一個 AccountRepository

    @Autowired
    private AuditLogRepository auditLogRepository; // 假設(shè)你有一個 AuditLogRepository


    /**
     * 示例：在一個事務(wù)中轉(zhuǎn)賬并記錄日志
     * 如果任何一步失敗，整個操作將回滾
     */
    @Transactional // 關(guān)鍵注解
    public void transferMoney(String fromAccountId, String toAccountId, double amount) {
        try {
            Account fromAccount = accountRepository.findById(fromAccountId)
                    .orElseThrow(() -> new RuntimeException("Source account not found"));
            Account toAccount = accountRepository.findById(toAccountId)
                    .orElseThrow(() -> new RuntimeException("Destination account not found"));

            if (fromAccount.getBalance() < amount) {
                throw new RuntimeException("Insufficient funds");
            }

            fromAccount.setBalance(fromAccount.getBalance() - amount);
            toAccount.setBalance(toAccount.getBalance() + amount);

            accountRepository.save(fromAccount);

            // 模擬一個可能發(fā)生的錯誤，以測試回滾
            // if (true) {
            //     throw new RuntimeException("Simulated error during transfer!");
            // }

            accountRepository.save(toAccount);

            // 記錄審計日志
            AuditLog log = new AuditLog("Transfer of " + amount + " from " + fromAccountId + " to " + toAccountId);
            auditLogRepository.save(log);

            System.out.println("Transfer successful and logged!");

        } catch (RuntimeException e) {
            // @Transactional 會在 RuntimeException 拋出時自動回滾
            // 你可以在這里記錄錯誤，但不需要手動回滾
            System.err.println("Transfer failed: " + e.getMessage());
            throw e; // 重新拋出，以便 Spring 能夠捕獲并回滾事務(wù)
        }
    }

    /**
     * 示例：只讀事務(wù)
     * 對于只需要讀取數(shù)據(jù)的操作，可以標(biāo)記為只讀，這可能有一些性能優(yōu)化。
     */
    @Transactional(readOnly = true)
    public Account getAccountDetails(String accountId) {
        return accountRepository.findById(accountId).orElse(null);
    }

    // 假設(shè)的實(shí)體和倉庫
    // Account.java, AuditLog.java
    // AccountRepository.java extends MongoRepository<Account, String>
    // AuditLogRepository.java extends MongoRepository<AuditLog, String>
}

// 在調(diào)用方或者一個更高層次的Service
@Service
public class TransactionalCallerService {

    @Autowired
    private AccountService accountService;

    private static final int MAX_RETRIES = 3;

    public void performTransferWithRetry(String from, String to, double amount) {
        int retries = 0;
        boolean success = false;
        while (retries < MAX_RETRIES && !success) {
            try {
                accountService.transferMoney(from, to, amount);
                success = true; // 如果沒有異常，標(biāo)記成功
            } catch (MongoTransactionException e) { // 捕獲事務(wù)相關(guān)的異常，特別是寫沖突
                retries++;
                System.err.println("Transaction failed due to conflict, retrying (" + retries + "/" + MAX_RETRIES + "): " + e.getMessage());
                if (retries >= MAX_RETRIES) {
                    System.err.println("Max retries reached. Transfer aborted.");
                    throw e; // 或者拋出一個自定義的業(yè)務(wù)異常
                }
                // 可以考慮在此處添加短暫的延遲
                try {
                    Thread.sleep(100 * retries); // 簡單的指數(shù)退避
                } catch (InterruptedException ie) {
                    Thread.currentThread().interrupt();
                    throw new RuntimeException("Retry interrupted", ie);
                }
            } catch (RuntimeException e) { // 捕獲其他業(yè)務(wù)邏輯異常
                System.err.println("Transfer failed due to business error: " + e.getMessage());
                throw e; // 這些通常不需要重試
            }
        }
    }
}