JAVA分布式开发中遇到的哪些坑(一)

一、Spring使用过程中的踩坑记录

JAVA分布式开发中遇到的哪些坑(一)_第1张图片
image
  • Spring通过注解使用多数据源

坑:@Autowired 按 byType 自动注入,而 @Resource 则默认按 byName 自动注入,@Primary是优先选择。

例如,在项目中是有两个Redis源,这两个Redis Bean分别为dataRedisTemplate和redisTemplate。

Redis Bean1:dataRedisTemplate,clusterNodes为${data-redis.cluster.nodes}

@Bean(name = "dataRedisTemplate")
public RedisTemplate dataRedisTemplate() {
    RedisTemplate template = new RedisTemplate();
    template.setConnectionFactory(sessionLettuceConnectionFactory);
    Jackson2JsonRedisSerializer jackson2JsonRedisSerializer = new Jackson2JsonRedisSerializer(Object.class);
    ObjectMapper om = new ObjectMapper();
    om.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);
    om.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
    jackson2JsonRedisSerializer.setObjectMapper(om);
    template.setKeySerializer(new StringRedisSerializer());
    template.setValueSerializer(jackson2JsonRedisSerializer);
    template.setHashKeySerializer(jackson2JsonRedisSerializer);
    template.setHashValueSerializer(new StringRedisSerializer());
    template.afterPropertiesSet();
    return template;
}

// factory
@Resource
@Qualifier(value = "dataLettuceConnectionFactory")
private RedisConnectionFactory dataLettuceConnectionFactory;

// clusterNodes
@Value("${spring.data-redis.cluster.nodes}")
private String clusterNodes;

Redis Bean2:redisTemplate,clusterNodes为${redis.cluster.nodes}

@Primary
@Bean(name = "redisTemplate")
public RedisTemplate redisTemplate() {
    RedisTemplate redisTemplate = new RedisTemplate<>();
    redisTemplate.setConnectionFactory(lettuceConnectionFactory);
    redisTemplate.setKeySerializer(new StringRedisSerializer());
    Jackson2JsonRedisSerializer jackson2JsonRedisSerializer = new Jackson2JsonRedisSerializer(Object.class);
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);
    objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
    jackson2JsonRedisSerializer.setObjectMapper(objectMapper);
    redisTemplate.setValueSerializer(jackson2JsonRedisSerializer);
    redisTemplate.setHashKeySerializer(new StringRedisSerializer());
    redisTemplate.setHashValueSerializer(new StringRedisSerializer());
    redisTemplate.afterPropertiesSet();
    return redisTemplate;
}

// factory
@Resource
@Qualifier(value = "lettuceConnectionFactory")
private RedisConnectionFactory lettuceConnectionFactory;

// clusterNodes
@Value("${spring.redis.cluster.nodes}")
private String clusterNodes;

在一个应用中要把数据放入到“Redis Bean1:dataRedisTemplate”对应的Redis中,于是我在这个应用中使用方式如下:

@Autowired
private RedisTemplate dataRedisTemplate;

// 根据key获取数据
Object obj = dataRedisTemplate.opsForValue().get(key);

实际上使用的是“Redis Bean2:redisTemplate”对应的Redis。
破解方式一:把@Autowired换成@Resource 注解。如下:

@Autowired
private RedisTemplate dataRedisTemplate;

// 把@Autowired换成@Resource

@Resource
private RedisTemplate dataRedisTemplate;

@Autowired和@Resource最大的区别就是:@Autowired 按 byType 自动注入,而 @Resource 则默认按 byName 自动注入。

这里还需要注意一个注解@Primary,官方的说明如下:

Indicates that a bean should be given preference when multiple candidates are qualified to autowire a single-valued dependency. If exactly one 'primary' bean exists among the candidates, it will be the autowired value.

@Primary 优先方案,被注解的实现,优先被注入

通常情况下@Autowired是通过byType的方法注入的,可是在多个实现类的时候,byType的方式不再是唯一,而需要通过byName的方式来注入,而这个name默认就是根据变量名来的。

也就是说,如果没有在redisTemplate()上面增加@Primary的话是没有问题的,因为有多个实现时,@Autowired是会通过byName的方式来注入的,但是按照上面说的,因为有了@Primary,@Autowired注解会优先使用Bean redisTemplate。

还有一种解决方案是增加@Qualifier(value = "dataRedisTemplate"),如下:

@Autowired
private RedisTemplate dataRedisTemplate;

// 换成:增加@Qualifier(value = "dataRedisTemplate")

@Autowired
@Qualifier(value = "dataRedisTemplate")
private RedisTemplate dataRedisTemplate;
  • Spring事务@Transactional失效问题

坑:若同一类中的其他没有@Transactional 注解的方法内部调用有@Transactional 注解的方法,有@Transactional 注解的方法的事务被忽略,不会发生回滚。

FooService.class

public interface FooService {
    void insertRecord();
    void insertThenRollback() throws Exception;
    void invokeInsertThenRollback() throws Exception;
    void invokeInsertThenRollbackTwo() throws Exception;
}

FooServiceImpl.class

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Component;
import org.springframework.transaction.annotation.Transactional;

@Component
public class FooServiceImpl implements FooService {
    @Autowired
    private JdbcTemplate jdbcTemplate;
    @Autowired
    private FooService fooService;

    @Override
    @Transactional
    public void insertRecord() {
        jdbcTemplate.execute("INSERT INTO FOO (BAR) VALUES ('AAA')");
    }

    @Override
    @Transactional(rollbackFor = Exception.class)
    public void insertThenRollback() throws Exception {
        jdbcTemplate.execute("INSERT INTO FOO (BAR) VALUES ('BBB')");
        throw new Exception();
    }

    @Override
    public void invokeInsertThenRollback() throws Exception {
        insertThenRollback();
    }

    @Override
    public void invokeInsertThenRollbackTwo() throws Exception {
        fooService.insertThenRollback();
    }
}

执行

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.AdviceMode;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.transaction.annotation.EnableTransactionManagement;

@SpringBootApplication
@EnableTransactionManagement(mode = AdviceMode.PROXY)
@Slf4j
public class DeclarativeTransactionDemoApplication implements CommandLineRunner {
    @Autowired
    private FooService fooService;
    @Autowired
    private JdbcTemplate jdbcTemplate;

    public static void main(String[] args) {
        SpringApplication.run(DeclarativeTransactionDemoApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        // 标记1:输出 AAA 1
        fooService.insertRecord();
        log.info("AAA {}",jdbcTemplate.queryForObject("SELECT COUNT(*) FROM FOO WHERE BAR='AAA'", Long.class));
        
        // 标记2:输出 BBB 0,事务生效        
        try {
            fooService.insertThenRollback();
        } catch (Exception e) {
            log.info("BBB {}",jdbcTemplate.queryForObject("SELECT COUNT(*) FROM FOO WHERE BAR='BBB'", Long.class));
        }

        // 标记3:输出 BBB 1,事务未生效
        // ***这个地方就是最容易踩坑的地方!!!***        
        try {
            fooService.invokeInsertThenRollback();
        } catch (Exception e) {
            log.info("BBB {}",jdbcTemplate.queryForObject("SELECT COUNT(*) FROM FOO WHERE BAR='BBB'", Long.class));
        }

        // 标记4:输出 BBB 1,事务生效(如果把标记3的代码注释掉,输出 BBB 0)
        // ***这是避免踩坑的一种方式***        
        try {
            fooService.invokeInsertThenRollbackTwo();
        } catch (Exception e) {
            log.info("BBB {}",jdbcTemplate.queryForObject("SELECT COUNT(*) FROM FOO WHERE BAR='BBB'", Long.class));
        }
    }
}

二、RocketMQ使用过程中的踩坑记录

JAVA分布式开发中遇到的哪些坑(一)_第2张图片
image
  • Rocket默认开启了VIP通道导致10909failed问题
    坑:Rocket默认开启了VIP通道,VIP通道端口为10911-2=10909。若Rocket服务器未启动端口10909,则报connect to <:10909> failed。

解决方案:不走VIP通道。

producer.setVipChannelEnabled(false);
consumer.setVipChannelEnabled(false);
  • Rocket instanceName参数未做配置导致重复消费问题

坑:一个是Rocket如果没有配置instanceName,那么会使用pid做instanceName,如果instanceName一样会重复消费,因为集群消费模式是按instanceName做为唯一消费实例。

查看源码,如果没有指定instanceName默认会把pid做为instanceName,如下:

if (this.instanceName.equals("DEFAULT")) {
    this.instanceName = String.valueOf(UtilAll.getPid());
}

public static int getPid() {
    RuntimeMXBean runtime = ManagementFactory.getRuntimeMXBean();
    String name = runtime.getName(); // format: "pid@hostname"
    try {
        return Integer.parseInt(name.substring(0, name.indexOf('@')));
    }
    catch (Exception e) {
        return -1;
    }
}

解决方案:运维配置有$MQ_INSTANCE_NAME 环境变量,不同机器不一样,所以可以使用:mq.consumer.instanceName:${MQ_INSTANCE_NAME:默认值}进行配置。

@Value("${rocketmq.consumer.instanceName:${MQ_INSTANCE_NAME:fota}}")
private String clientInstanceName;

consumer.setInstanceName(clientInstanceName);

你可能感兴趣的:(JAVA分布式开发中遇到的哪些坑(一))