最新30道面试题2021年常见bug问题面试题及答案汇总

public void afterPropertiesSet() {

	super.afterPropertiesSet();

	boolean defaultUsed = false;

	if (defaultSerializer == null) {

		defaultSerializer = new JdkSerializationRedisSerializer(
				classLoader != null ? classLoader : this.getClass().getClassLoader());
	}

	if (enableDefaultSerializer) {

		if (keySerializer == null) {
			keySerializer = defaultSerializer;
			defaultUsed = true;
		}
		if (valueSerializer == null) {
			valueSerializer = defaultSerializer;
			defaultUsed = true;
		}
		if (hashKeySerializer == null) {
			hashKeySerializer = defaultSerializer;
			defaultUsed = true;
		}
		if (hashValueSerializer == null) {
			hashValueSerializer = defaultSerializer;
			defaultUsed = true;
		}
	}

	if (enableDefaultSerializer && defaultUsed) {
		Assert.notNull(defaultSerializer, "default serializer null and not all serializers initialized");
	}

	if (scriptExecutor == null) {
		this.scriptExecutor = new DefaultScriptExecutor<K>(this);
	}

	initialized = true;
}

public class RedisServiceImpl {

    private static final Logger log = LoggerFactory.getLogger(RedisDao.class);

    private RedisTemplate redisTemplate;

    private RedisTemplate<String, Object> redisTemplateMap;

    @Autowired(required = false)
    public void setRedisTemplate(RedisTemplate redisTemplate) {
        RedisSerializer stringSerializer = new StringRedisSerializer();
        redisTemplate.setKeySerializer(stringSerializer);
        redisTemplate.setValueSerializer(stringSerializer);
        redisTemplate.setHashKeySerializer(stringSerializer);
        redisTemplate.setHashValueSerializer(stringSerializer);
        this.redisTemplate = redisTemplate;
    }
}

xmlns:task="http://www.springframework.org/schema/task" 
http://www.springframework.org/schema/task  
http://www.springframework.org/schema/task/spring-task-3.2.xsd 

<task:annotation-driven />

<context:component-scan base-package="com.jingxuan" />

package com.jingxuan;

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class JingxuanTask {
    @Scheduled(cron = "0/5 * * * * ? ") // 间隔5秒执行
    public void task() {
        System.out.println("----定时任务开始执行-----");
		//执行具体业务逻辑----------  
        System.out.println("----定时任务执行结束-----");
    }
}

<?xml version="1.0" encoding="UTF-8"?> <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

Caused by: java.io.FileNotFoundException: /home/tomcat/jingxuan-tomcat/webapps/jingXuanAPI/WEB-INF/lib/activemq-client-5.9.1.jar (Too many open files)
        at java.util.zip.ZipFile.open(Native Method)
        at java.util.zip.ZipFile.<init>(ZipFile.java:225)
        at java.util.zip.ZipFile.<init>(ZipFile.java:155)

[root@mrwang ~]# ulimit -a
core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 14429
max locked memory       (kbytes, -l) 16384
max memory size         (kbytes, -m) unlimited
open files                      (-n) 65535
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 14429
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

[root@mrwang ~]# lsof -p 8288
COMMAND  PID USER   FD   TYPE             DEVICE  SIZE/OFF      NODE NAME
java    8288 root  cwd    DIR              253,1       160   1717293 /home/tomcat/apache-tomcat-server
java    8288 root  rtd    DIR              253,1       244       128 /
java    8288 root  txt    REG              253,1      8712   1507063 /home/jdk/jdk1.8.0_291/bin/java
java    8288 root  mem    REG              253,1    168368  33739024 /usr/lib64/libresolv-2.28.so
java    8288 root  mem    REG              253,1     41304  33739018 /usr/lib64/libnss_dns-2.28.so
java    8288 root  mem    REG              253,1   3559360  67178238 /home/jdk/jdk1.8.0_291/jre/lib/resources.jar
java    8288 root  mem    REG              253,1    104256  34147343 /usr/lib64/libgcc_s-8-20190507.so.1
java    8288 root  mem    REG              253,1    283368  84407379 /home/jdk/jdk1.8.0_291/jre/lib/amd64/libsunec.so
java    8288 root  mem    REG              253,1    113008  84407389 /home/jdk/jdk1.8.0_291/jre/lib/amd64/libnet.so
java    8288 root  mem    REG              253,1     93872  84407404 /home/jdk/jdk1.8.0_291/jre/lib/amd64/libnio.so
...

[root@mrwang ~]# vim /etc/security/limits.conf  

* soft nofile 4096  
* hard nofile 4096  

 * - nofile 8192

jingxuan soft nofile 8192  
jingxuan hard nofile 8192  

set time_zone='+8:00';

characterEncoding=utf-8&serverTimezone=UTC

LANG="zh_CN.UTF-8"

source /etc/locale.conf