2019年多家公司整理的350道Java面试题手册.pdf

Java?1.1?tomcat?1.2?JVM?1.3?Mysql?2.1?SpringCloud?2.2?SpringBoot?2.3?Dubbo?4.1?Spring?4.2?SpringMVC?4.3?MyBatis?5.1?5.2?5.3?1.1?tomcat?1?tomcat?1.JVM?-Xms?JVM?-Xmx?JVM?80%?catalina.bat?JAVA_OPTS=-Xms256m-Xmx512m?256MB?512MB?2.?DNS?web?IP?IP?DNS?IP?DNS?DNS?server.xml?enableLookups?Tomcat4Tomcat53.?Con nector?Tomcat?Java?CPU?Tomcat4?minProcessors?maxProcessors?minProcessors?5?1?5?maxProcessors?maxProcessors?web server?Windows?2000?Linux?1000?Tomcat5?maxThreads Tomcat?Tomcat?acceptCount?connnection Timeout?0?30000?minSpareThreadsTomcat?maxSpareThreads?Tomcat?socket?web?2?comcat?tomcat?server.xml?minProcessors?10maxProcessors?75acceptCount?maxProcessors?100enableLookups?true?false?falseconnectionTimeout?0?30000?maxProcessors?acceptCount?web server?Windows?2000?Linux?1000?tomcat5?3?tomcat?java.lang.OutOfMemoryError:Javaheap space?JAVA?1?Heap size?TOMCAT_HOME/bin/catalina.shsetJAVA_OPTS=-Xms32m-Xmx512m?2?java-Xms32m-Xmx800m className?JAVA?className?Eclispe?Eclipse-run-arguments?VM arguments?-Xms32m-Xmx800m?Eclilpse?VMarguments?-Xms32m-Xmx800m?java.lang.OutOfMemoryError:PermGen spacePermGen space?Permanent Generation space,?,?JVM?Class?Meta?,Class?Loader?PermGen space?,?(Instance)?Heap?,GC(Garbage Collection)?PermGen space?CLASS?,?PermGen space?,?web?JSP?preco mpile?WEB APP?jar,?jvm?(4M)?MaxPermSize?TOMCAT_HOME/bin/catalina.sh?“echoUsing CATALINA_BASE:$CATALINA_BASE”?JAVA_OPTS=-server-XX:PermSize=64M-XX:MaxPermSize=128m?jar?tomcat/shared/lib?jar?java.lang.OutOfMemoryError:Java heap spaceHeap size?JVM?java?JVM?.JVM?Heap size?(?-Xms)?1/64?(-Xmx)?1/4?JVM?-Xmn-Xms-Xmx?Heapsize?Young Generation?TenuredGeneraion?JVM?98?GC?Heap size?2?Heap Size?80?-Xms?-Xmx?-Xmn?1/4?-Xmx?Heap size?TOMCAT_HOME/bin/catalina.sh?“echoUsing CATALINA_BASE:$CATALINA_BASE”?JAVA_OPTS=-server-Xms800m-Xmx800m-XX:MaxNewSize=256m?1G?java jvm?JAVA_OPTS=-server-Xms800m-Xmx800m-XX:PermSize=64M-XX:MaxNewSize=256m-XX:MaxPermSize=128m-Djava.awt.headless=true?web?tomcat?myeclipse?tomcat?tomcat?TOMCAT_HOME/bin/catalina.bat?set JAVA_OPTS=-server-Xms2048m-Xmx4096m-XX:PermSize=512M-XX:MaxPermSize=1024M-Duser.timezone=GMT+08?set JAVA_OPTS=-Xmx1024M-Xms512M-XX:MaxPermSize=256m?myeclipse?Myeclipse-preferences-myeclipse-servers-tomcat-tomcat.-JDK?Optional Java VM arguments?-Xmx1024M-Xms512M-XX:MaxPermSize=256m?myeclipse?Tomcat?ava.lang.OutOfMemoryError:Java heap space?Myeclipse-preferences-myeclipseservers-tomcat-tomcat.-JDK?Optional Java VM arguments?-Xmx1024M-Xms512M-XX:MaxPermSize=256m4?tomcat?tomcat_home/conf/web.xml?listings?false?listingsfalselistingsfalse5?Tomcat?tomcat?tomcat?conf?server.xml?Context?web?webapps?conf?Catalina?localhost?xml?xml?3?path?URL?XML?2?3?:?tomcat?tomcat?war?6?Tomcat?Tomcat?web?:?web.xml?jsp?Servlet?tomcat?jvm?CPU?CPU?-Xmx-Xms-XX:MaxPermSize?full GC?Nginx?css?js?tomcat?gzip?tomcat?Nginx?gzip?300?kb?kb?tomcat?Nginx?tomcat?session?nginx+tomcat+memcached?web?tomcat?tomcat7?conf/server.xml?dns?1.2?JVM?1?Java?Java?7?1.?Class?2.?Class?.?:?Class?.?:?3.?Java?public static int value=123;/?value?0?123?4.?5.?java?6.?7.?2?java?static?.class?final?RAM?new?Java?,?1.Java?Perm Genspace?JVM?JVM?3?JVM?Class?Java?Class?JVM?JVM?.class?Java?ClassLoader?new?JVM?class.forName()?JVM?JVM?Java?.class?Java?JVM?class?3?class?4?GC?GC?GC?(GabageCollection)?Java?GC?Java?5?Java?Java?JVM?6?(?GC?)?:1.?“?”,?.?A?B?B?A?A?B?2.?(?)?:?GC Roots?GC Roots?Java?GC Roots?:?JNI?GC Root?.?GC Root?finalize()?finalize()?finalize()?F-Queue?Finalize()?finalize()?F-Queue?GC?F-Queue?”?”?7?2?Java?C+?Java?Java?“?”?8?GC?GC?GC?(heap)?”?”?”?”?GC?“?”?GC?System.gc()?GC?Java?GC?9?Java?Java?Java?GC?:import java.io.IOException;public class GarbageTest /*param args *throws IOException */public static void main(String args)throws IOException /TODO Auto-generated method stubtry gcTest();catch(IOException e)/TODO Auto-generated catch block e.printStackTrace();System.out.println(has exited gcTest!);System.in.read();System.in.read();System.out.println(out begin gc!);for(int i=0;i100;i+)System.gc();System.in.read();System.in.read();private static void gcTest()throws IOException System.in.read();System.in.read();Person p1=new Person();System.in.read();System.in.read();Person p2=new Person();p1.setMate(p2);p2.setMate(p1);System.out.println(before exit gctest!);System.in.read();System.in.read();System.gc();System.out.println(exit gctest!);private static class Person byte data=new byte20000000;Person mate=null;public void setMate(Person other)mate=other;Java?:?Java?java?(?map?)?Java?(?null?):?public class Stack private Object elements=new Object10;private int size=0;public void push(Object e)ensureCapacity();elementssize+=e;public Object pop()if(size=0)throw new EmptyStackException();return elements-size;private void ensureCapacity()if(elements.length=size)Object oldElements=elements;elements=new Object2*elements.length+1;System.arraycopy(oldElements,0,elements,0,size);?10?:?K?G?public class Badpublic static Stack s=Stack();statics.push(new Object();s.pop();/?s.push(new Object();/?static?Stack?100?100?Stack?100?!?:?HashSet?HashSet?contains?HashSet?HashSet?10?Person p=new Person(“?”);?11?System.gc()?Runtime.gc()?JVM?JVM?12?finalize()?(finalization)?(garbage colector)?finalize()?Java?filalize()?finalize()?Java?JNI(Java Native Interface)?non-Java?(C?C+)?finalize()?13?null?14?(DGC)?DGC?RMI?DGC?RMI?DGC?15?(serial)?(throughput)?(?100M?)?16?Java?17?Java?Minor GC?Major GC?Eden?Eden?Minor GC?Minor GC?Eden?Gc?;Full GC/Major GC?GC?Minor GC?Full GC?Minor GC?18?JVM?(Full GC)?:Java 8?native?19?Java?-?:?:1.?;2.?GC?:?1:1?8:1:1?Eden?Survior?Eden?Eden?Eden?Survivor?(java?)?-?:?-?;?:?20?:?(BootstrapClassLoader)?Java?Java?(extensions class loader):?Java?Java?Java?(system class loader):?Java?(CLASSPATH)?Java?Java?ClassLoader.getSystemClassLoader()?java.lang.ClassLoader?21?3?Mysql?1?SpringCloud?1?Spring Cloud?Spring cloud?Spring Boot?Spring?Spring cloud Task?2?Spring Cloud?Spring Boot?-?-?-?-?-?-Devops?3?Spring Cloud?Eureka?Eureka?Eureka?4?5?Hystrix?Hystrix?9?1000.?hystrix?Hystrix?Fallback?employee-consumer?employee-consumer?employee-producer?Hystrix?6?Hystrix?employee-consumer?Hystrix?firstPage method()?Hystrix?firtsPage?7?Netflix Feign?Feign?Retrofit?JAXRS-2.0?WebSocket?java?Feign?http apis?employee-consumer?employee-producer?REST?REST?URL?REST?1.Controller2.public class ConsumerControllerClient 3.4.Autowired5.private LoadBalancerClient loadBalancer;6.7.public void getEmployee()throws RestClientException,IOException 8.9.ServiceInstance serviceInstance=loadBalancer.choose(employee-producer);10.11.System.out.println(serviceInstance.getUri();12.13.String baseUrl=serviceInstance.getUri().toString();14.15.baseUrl=baseUrl+/employee;16.17.RestTemplate restTemplate=new RestTemplate();18.ResponseEntity response=null;19.try20.response=restTemplate.exchange(baseUrl,21.HttpMethod.GET,getHeaders(),String.class);22.catch(Exception ex)23.24.System.out.println(ex);25.26.System.out.println(response.getBody();27.?NullPointer?Netflix Feign?NetflixRibbon?Feign?8?Spring Cloud Bus?:?Spring Cloud Config?Spring Cloud Config?GIT?Employee Config Module?Eureka?GIT?Eureka?Eureka?/?url?Employee Producer1?8080?http:/localhost:8080/refresh?Employee Producer2http:/localhost:8081/refresh?Spring CloudBus?Spring Cloud Bus?Employee Producer1?/?/?2?SpringBoot?1?Spring Boot?spring?https:/spring.io/projects?Spring?Spring?Maven?spring?spring?Spring Boot?Spring Boot?spring?spring?Spring Boot?Spring?2?Spring Boot?Spring Boot?:?JavaConfig?XML?Maven?Web?Tomcat?Glassfish?web.xml?Configuration?Bean?Spring?Autowired?bean?Spring?:-Dspring.profiles.active=enviornment?Spring?(applicationenvironment.properties)?3?JavaConfig?Spring JavaConfig?Spring?Spring IoC?Java?XML?JavaConfig?:?JavaConfig?Java?Bean?XML?XML?Java?JavaConfig?Java?XML?Spring?JavaConfig?JavaConfig?XML?JavaConfig?Spring?Java 5.0?bean?4?Spring Boot?DEV?tomcat?Spring Boot?(DevTools)?Java?Spring Boot?Spring Boot?DevTools?H2?org.springframework.boot spring-boot-devtools true5?Spring Boot?Spring boot actuator?spring?Spring boot?HTTP URL?REST?6?Spring Boot?Actuator?HTTP?ACTUATOR?HttpServletRequest.isUserInRole?management.security.enabled=false?7?Spring Boot?Spring Boot?application.properties?server.port=80908?YAML?YAML?YAML?YAML?9?Spring Boot?Spring Boot?spring-boot-starter-security?WebSecurityConfigurerAdapter?10?Spring Boot?ActiveMQ?Spring Boot?ActiveMQ?spring-boot-starter-activemq?11?Spring Boot?Spring Boot?Spring Data-JPA?org.springframework.data.domain.Pageable?12?Swagger?Spring Boot?Swagger?API?Swagger UI?Swagger?RESTful Web?Swagger?Swagger?13?Spring Profiles?Spring Profiles?(dev?test?prod?)?bean?bean?PRODUCTION?bean?Swagger?QA?Spring Boot?14?Spring Batch?Spring Boot Batch?/?15?FreeMarker?FreeMarker?Java?MVC?Freemarker?html?freemarker?16?Spring Boot?Spring?ControllerAdvice?ControlerAdvice?17?starter maven?spring-boot-starter-activemq spring-boot-starter-securityspring-boot-starter-web?18?CSRF?CSRF?Web?CSRF?19?WebSockets?WebSocket?TCP?WebSocket?-?WebSocket?WebSocket?-?TCP?-?HTTP?Light-?http?WebSocket?20?AOP?(AOP)?21?Apache Kafka?Apache Kafka?-?-?Apache?Kafka?22?Spring Boot?Spring Boot?(?)?(?)?50?50?3?Dubbo?1?Dubbo?zookeeper?dubbo?zk?;?;?;?;?2?dubbo?l Random LoadBalance?(?dubbo?)l RoundRobin LoadBalance?:?l LeastActive LoadBalance?l ConsistentHash LoadBalance?Hash?Hash?160?3?Dubbo?Dubbo?Token?Dubbo?4?dubbo?l Failsafe Cluster?AppleScript?Failover?1.dubbo?(?)?Dubbo?failover?l Failover Cluster(?)?(?)?retries=2?(?)?:cluster=failover?,?failoverl Failfast Cluster?dubbo:service cluster=failfast/?:cluster=failfast?cluster=failover?retries=0?,retries=0?l Failsafe Cluster?:l Failback Cluster?:l Forking Cluster?forks=2?:l?dubbo:method name=.loadbalance?dubbo:method name=.loadbalance=1.dubbo?dubbo?:?dubbo?(1024Mbit=128MByte)?7MByte(?)?1?20?2.dubbo?dubbo?:?dubbo?500KByte?(1024Mbit=128MByte)?7MByte(?)?TPS(?)?:128MByte/500KByte=262?TPS(?)?:7MByte/500KByte=14?3.dubbo?dubbo?:?Morgan?6?1.5?hessian?IO?C10K?4.dubbo?dubbo?:?(?100K)?dubbo?:?dubbo?:?:?:?:TCP?:NIO?:Hessian?5.RMI?RMI?JDK?java.rmi.*?JDK?Java?:?:?:TCP?:?:Java?:?:?RMI?6.Hessian?Hessian?Hessian?Hessian?Http?Servlet?Dubbo?Jetty?Hessian?:?:?:HTTP?:?:Hessian?:?:?hessian?7.http?Spring?HttpInvoker?http?:?:?:HTTP?:?:?(JSON)?:?URL?:?JS?8.Webservice?CXF?frontend-simple?transports-http?WebService?:?:?:HTTP?:?:SOAP?:?9.Thrif Thrift?Facebook?Apache?RPC?dubbo?thrift?thrift?service name?magic number?1?Synchronized?Java?Synchronized?Synchronized?JVM?Synchronized?Synchronized?monitorenter?monitorexit?monitorenter?+1?monitorexit?-1?0?Java?Synchronize?2?“?”?“?”?monitorenter?monitorexit?Reference?Synchronized?1.?Synchronized?Synchronized(?)?Synchronized(this)?2.?:?Synchronized?;?Synchronized?Synchronized?Synchronized?3?Synchronized?Synchronized?method2?method2?method1?Synchronized?monitorenter?(?)?+1?4?JVM?Java?Java 6?Monitor?/?Java?JDK?JDK?Monitor?:?(Biased Locking)?JDK?Synchronized?JVM?JVM?CAS?Mark Word?ID?JVM?CAS?Mark Word?;?5?Synchronized?6?:?:?7?Synchronized?CAS?Synchronized?:?;?CAS(Compareand Swap?)?:?CAS?CPU?JNI?Native?C+?JDK?Unsafe?8?:1.?2.?CAS?CPU?3.ABA?CAS?A?B?A?CAS?9?Synchronized?ReentrantLock?:?Synchronized?JVM?ReentrantLock?Lock?volitile?int?int?AQS?10?AQS?AQS(AbstractQueuedSynchronizer?)?Lock?(?ReentrantLock?ReadWriteLock)?Semaphore?CountDownLatch?FutureTask?AQS?1.AQS?volatile int 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parties,Runnable barrierAction)?)?CyclicBarrier?N?N?(?CountDownLatch?)?17?Java?Java?“?”?Worker?AQS?HashSet workers?;?workQueue(BlockingQueueworkQueue)?:?workQueue?Workers?18?Java?:corePoolSize:?maximumPoolSize:?keepAliveTime:?workQueue:?execute?Runnable?19?Worker?execute()?:?corePoolSize?;?corePoolSize?;?maximumPoolSize?;?maximumPoolSize?RejectExecutionException?(keepAliveTime)?corePoolSize?corePoolSize?20?Java?1.SingleThreadExecutor?corePoolSize:1?maximumPoolSize:1?keepAliveTime:0L?workQueue:new LinkedBlockingQueue()?2.FixedThreadPool?FixedThreadPool?FixedThreadPool?corePoolSize:nThreads maximumPoolSize:nThreads keepAliveTime:0L workQueue:new LinkedBlockingQueue()?3.CachedThreadPool?CachedThreadPool?(60?)?(?JVM)?SynchronousQueue?1?daemon?SERVER?Executor?corePoolSize:0 maximumPoolSize:Integer.MAX_VALUE keepAliveTime:60L workQueue:new SynchronousQueue()?1?4.ScheduledThreadPool?ScheduledThreadPool:?DEFAULT_KEEPALIVEMILLIS?corePoolSize:corePoolSize maximumPoolSize:Integer.MAX_VALUE keepAliveTime:DEFAULT_KEEPALIVE_MILLIS workQueue:new DelayedWorkQueue()21?Java?:1.execute():ExecutorService.execute?:2.submit():ExecutorService.submit()?Future?isDone()?Future?get()?isDone()?get()?get()?22?Java?Java?Java?Java?Java?:?(?)?23?volatile?volatile?Java?volatile?:1.?2.?Java?8?:lock?unlock?read?write?load?store?load?store?read?write?use?assgin?volatile?8?volatile?24?volatile?volatile?volatile?volatile?(?volatile?)?Java?volatile?25?volatile?Synchronized?Synchronized?volatile?ThreadLocal?Synchonized?ThreadLocal?Synchronized?Synchronized?“?”?ThreadLocal?“?”?26?ThreadLocal?ThreadLocal?Java?ID?Cookie?ThreadLocal?ThreadLocal?Map?27?ThreadLocal?ThreadLocal?ThreadLocal?remove!ThreadLocal?ThreadLocalMap?ThreadLocalMap?key?ThreadLocal?ThreadLocalMap!?OOM?remove?worker?4.1?Spring?1?Spring?Spring?Spring?Java?Java?Spring?Spring?Spring?Spring?Spring?20?/?,?Web?AOP(?)?2?Spring?Spring?:Dependency Injection(DI)?JavaBean properties?EJB?IoC?IoC?CPU?Spring?Spring?ORM?logging?J2EE?Q uartz?JDK Timer?Spring?Spring?JavaBean?POJO?Spring?Web?Web MVC?web?Struts?web?Spring?(?DB?)?(?JTA?DB?)?3?(IOC)?“?”?Java?:1.?2.Setter?3.?4?Spring?IoC?Spring?org.springframework.beans?org.springframework.context?Spring?IoC?BeanFactory?ApplicationContex?BeanFactory(?)?BeanFactory?Spring?AOP?message resource?(?)?Web?WebApplicationContext?org.springframework.