[Spring] Set exposeProxy property on Advised to true

問題描述

我在工作上有一個需求需要使用多執行緒完整多個工項，每一個工作都是獨立事務交易，所以我使用Java 8 CompletableFuture提供的方法實作Runnable，再利用Spring AOP代理機制處理事務交易，但當我發送Http Request到我的AP Server時，卻收到下述報錯訊息，從中可以得知發生此錯誤的原因有兩種可能，一、沒有打開代理Java @EnableAspectJAutoProxy(exposeProxy = true, proxyTargetClass = true)，另一個可能是不是在同一條執行緒使用代理機制，後來我才意識到我使用了不同的執行緒代理是無法生效的。

java.util.concurrent.ExecutionException: java.lang.IllegalStateException: Cannot find current proxy: Set exposeProxy property on Advised to 'true' to make it available, and ensure that AopContext.currentProxy() is invoked in the same thread as the AOP invocation context.

我就好奇為什麼AOP代理機制為不能跨執行緒，於是我去翻AopContext的source code，我才發現原來它是從ThreadLocal取得目前的代理類別，ThreadLocal本身特性就專屬於一個執行緒使用，其他的執行緒不能存取、修改。

public final class AopContext {
	private static final ThreadLocal<Object> currentProxy = new NamedThreadLocal<>("Current AOP proxy");

	private AopContext() {
	}
	
	public static Object currentProxy() throws IllegalStateException {
		Object proxy = currentProxy.get();
		if (proxy == null) {
			throw new IllegalStateException(
					"Cannot find current proxy: Set 'exposeProxy' property on Advised to 'true' to make it available, and " +
							"ensure that AopContext.currentProxy() is invoked in the same thread as the AOP invocation context.");
		}
		return proxy;
	}
}

範例

以下範例模擬我當時工作時發生的錯誤，在raiseEmployeeSalary()先到MongoDB撈所有員工的資料後，以多執行緒方式替員工加薪數額，由raiseSalary()完成，CompletableFuture.allOf意思是等所有員工加完薪水後，繼續往下作。如同上一節我所描述的，在透過代理機制去呼叫raiseSalary()就會報錯。

@Service
public class EmployeeService {
    @Autowired
    private EmployeeDao employeeDao;

    @Transactional(rollbackFor = Exception.class, propagation = Propagation.REQUIRED)
    public void raiseEmployeeSalary(RaiseSalaryBo raiseSalaryBo) throws ExecutionException, InterruptedException {
        List<Employee> employees = employeeDao.listAllEmployees();

        List<CompletableFuture<?>> tasks = new ArrayList<>();
        for (Employee employee : employees) {
            tasks.add(CompletableFuture.runAsync(()->((EmployeeService)AopContext.currentProxy()).raiseSalary(employee, raiseSalaryBo.getBonus())));
        }

        CompletableFuture.allOf(tasks.toArray(new CompletableFuture<?>[0])).get();
    }

    @Transactional(rollbackFor = Exception.class, propagation = Propagation.REQUIRES_NEW)
    public void raiseSalary(Employee employee, BigDecimal bonus) {
        employeeDao.raiseSalary(employee, bonus);
    }
}

解決方法

解決方法十分簡單，如若真的需要切割出子事務交易，那就不能使多執行緒來處理，依據上述範例必須把CompletableFuture移除，程式才能正常執行。

@Service
public class EmployeeService {
    @Autowired
    private EmployeeDao employeeDao;

   @Transactional(rollbackFor = Exception.class, propagation = Propagation.REQUIRED)
    public void raiseEmployeeSalary(RaiseSalaryBo raiseSalaryBo) {
        List<Employee> employees = employeeDao.listAllEmployees();

        for (Employee employee : employees) {
            ((EmployeeService) AopContext.currentProxy()).raiseSalary(employee, raiseSalaryBo.getBonus());
        }
    }

    @Transactional(rollbackFor = Exception.class, propagation = Propagation.REQUIRES_NEW)
    public void raiseSalary(Employee employee, BigDecimal bonus) {
        employeeDao.raiseSalary(employee, bonus);
    }
}

資料庫更新後的結果