Java多线程,线程池ThreadPoolExecutor使用详解

ThreadPoolExecutor.class构造方法参数讲解

参数名 作用
corePoolSize 核心线程池大小
maximumPoolSize 最大线程池大小
keepAliveTime 线程池中超过corePoolSize数目的空闲线程最大存活时间;可以allowCoreThreadTimeOut(true)使得核心线程有效时间
TimeUnit keepAliveTime时间单位
workQueue 阻塞任务队列
threadFactory 新建线程工厂
RejectedExecutionHandler 当提交任务数超过maxmumPoolSize+workQueue之和时,任务会交给RejectedExecutionHandler来处理

1.当线程池小于corePoolSize时,新提交任务将创建一个新线程执行任务,即使此时线程池中存在空闲线程。
2.当线程池达到corePoolSize时,新提交任务将被放入workQueue中,等待线程池中任务调度执行
3.当workQueue已满,且maximumPoolSize>corePoolSize时,新提交任务会创建新线程执行任务
4.当提交任务数超过maximumPoolSize时,新提交任务由RejectedExecutionHandler处理
5.当线程池中超过corePoolSize线程,空闲时间达到keepAliveTime时,关闭空闲线程
6.当设置allowCoreThreadTimeOut(true)时,线程池中corePoolSize线程空闲时间达到keepAliveTime也将关闭

示例代码:

import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class testThreadPool {

   /**
    * 线程计数 
    */
   private static int count = 0;
   public static void main(String[] args) {
      
      /**
       * 通常会使用一个队列,进行排序
       */
      BlockingQueue<Runnable> queue = new ArrayBlockingQueue<>(25);
      
      /**
       * 如果使用无界的队列,当出现攻击时,容易导致内存泄漏。
       */
      //LinkedBlockingDeque<Runnable> queue = new LinkedBlockingDeque<>();
      
      /**
       * 线程池
       */
      ThreadPoolExecutor pool = new ThreadPoolExecutor(5, 10, 30, TimeUnit.MINUTES, queue);
      
      /**
       * 重写Handler抛出来的线程重新加进去
       */
      pool.setRejectedExecutionHandler(new RejectedExecutionHandler() {
         
         @Override
         public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
            // TODO Auto-generated method stub
            while (true) {
               if (queue.size() < 24) {
                  System.out.println("++++++++++++++Runnable");
                  executor.execute(r);
                  break;
               }
            }
         }
      });

      /**
       * 定义一个定时器,每2秒创建10个进程
       */
      Timer timer = new Timer();
      timer.schedule(new TimerTask() {
         
         @Override
         public void run() {
            // TODO Auto-generated method stub
            
            for(int i = 0;i<10;i++) {
               count++;
               doWork work = new doWork();
               pool.execute(work);
               
            }
            
            if (count >= 200) {
               timer.cancel();
            }
         }
      }, 0,2000);
      
      /**
       * 定时检查线程的状况
       */
      new Timer().schedule(new TimerTask() {
         @Override
         public void run() {
            // TODO Auto-generated method stub
            System.err.println(">>当前队列:"+queue.size());
            System.err.println(">>线程数:"+count);
            System.err.println(">>当前ActiveCount:"+pool.getActiveCount());
            System.err.println(">>当前TaskCount:"+pool.getTaskCount());
            System.err.println(">>当前PoolSize:"+pool.getPoolSize());
         }
      }, 1000,1000);
      
   }
}

class doWork implements Runnable{
   

   @Override
   public void run() {
      // TODO Auto-generated method stub
      
      try {
         /**
          * 模拟真实环境,睡眠3秒
          */
         Thread.sleep(3000);
         System.out.println("线程id:"+Thread.currentThread().getId()+" 线程名称:"+Thread.currentThread().getName());
      } catch (InterruptedException e) {
         // TODO Auto-generated catch block
         e.printStackTrace();
      }
      
   }

}

 

API文档:

http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ThreadPoolExecutor.html

myBatis数据库自动断开的解决办法

使用Spring+SpringMVC+myBatis+Mysql开发一个应用服务端,由于在测试阶段没有上线,所以没有人会链接服务器。

放假回来才发现数据库被关闭了,而且要重启tomcat才有效,都不知道myBatis为什么会没有自动重连数据库的功能。

异常信息:

23-Sep-2017 09:43:39.880 SEVERE [http-nio-8081-exec-93] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [dispatcher] in context with path [/project] threw exception [Request processing failed; nested exception is org.springframework.dao.DataAccessResourceFailureException:
### Error querying database. Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
### The error may exist in file [/www/apache-tomcat-8081/webapps/project/WEB-INF/classes/com/test/system/mapper/xml/cateMapper.xml]
### The error may involve com.test.system.mapper.SdGoodsCateMapper.getCateByGroup
### The error occurred while executing a query
### SQL: SELECT b.* FROM …..;
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
; SQL []; No operations allowed after connection closed.; nested exception is com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.] with root cause
java.net.SocketException: Broken pipe (Write failed)
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:111)
at java.net.SocketOutputStream.write(SocketOutputStream.java:155)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3728)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2509)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2680)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2490)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2448)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1381)
at com.mysql.jdbc.DatabaseMetaData.getUserName(DatabaseMetaData.java:6274)
at org.apache.commons.dbcp.DelegatingConnection.toString(DelegatingConnection.java:123)
at org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.toString(PoolingDataSource.java:355)
at java.lang.String.valueOf(String.java:2994)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:87)
at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:68)
at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:315)
at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:75)
at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:61)
at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:303)
at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:154)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:102)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:82)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:120)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:113)
at sun.reflect.GeneratedMethodAccessor2495.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:408)
at com.sun.proxy.$Proxy408.selectList(Unknown Source)
at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:206)
at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:122)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:64)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53)
at com.sun.proxy.$Proxy434.getCateByGroup(Unknown Source)
at com.test.system.service.HomeServiceImpl.getHomeAlbumByHot(HomeServiceImpl.java:95)
at com.test.app.controller.HomeController.getAlbumByHot(HomeController.java:60)
at sun.reflect.GeneratedMethodAccessor2778.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:222)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:814)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:737)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:860)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1533)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1489)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)

原因分析:

查看了Mysql的文档,以及Connector/J的文档以及在线说明发现,出现这种异常的原因是:

Mysql服务器默认的“wait_timeout”是8小时,也就是说一个connection空闲超过8个小时,Mysql将自动断开该connection。这就是问题的所在,在C3P0 pools中的connections如果空闲超过8小时,Mysql将其断开,而C3P0并不知道该connection已经失效,如果这时有Client请求connection,C3P0将该失效的Connection提供给Client,将会造成上面的异常。

解决方案:

加上如下配置:

//SQL查询,用来验证从连接池取出的连接,在将连接返回给调用者之前.如果指定,则查询必须是一个SQL SELECT并且必须返回至少一行记录

validationQuery = select 1

//指明连接是否被空闲连接回收器(如果有)进行检验.如果检测失败,则连接将被从池中去除.

testWhileIdle = true

//在空闲连接回收器线程运行期间休眠的时间值,以毫秒为单位.如果设置为非正数,则不运行空闲连接回收器线程

timeBetweenEvictionRunsMillis = 3600000

//1000 * 60 * 30  连接在池中保持空闲而不被空闲连接回收器线程,(如果有)回收的最小时间值,单位毫秒

minEvictableIdleTimeMillis = 18000000

//指明是否在从池中取出连接前进行检验,如果检验失败,则从池中去除连接并尝试取出另一个.

testOnBorrow = true

 

validationQuery参考:

validationQuery是用来验证数据库连接的查询语句,这个查询语句必须是至少返回一条数据的SELECT语句。每种数据库都有各自的验证语句,下表中收集了几种常见数据库的validationQuery。

DataBase validationQuery
hsqldb select 1 from INFORMATION_SCHEMA.SYSTEM_USERS
Oracle select 1 from dual
DB2 select 1 from sysibm.sysdummy1
MySql select 1
Microsoft SqlServer select1
postgresql select version()
ingres select 1
derby values 1
H2 select 1

 

BasicDataSource Configuration Parameters:

http://commons.apache.org/proper/commons-dbcp/configuration.html

 

使用 Spring MVC HttpMessageConverter 功能构建 RESTful web 服务

随附文章,“使用 Spring 3 构建 RESTful web 服务”(参见 参考资料),介绍了使用 Spring 构建 RESTful web 服务的方式。还解释了如何使用 ContentNegotiatingViewResolver 生成多个具象,这是 RESTful web 服务的一个重要功能。本文还阐述了使用 HttpMessageConverter 生成多个具象的另一种方式,并且本文中的示例展示了如何使用 RestTemplate 和 HttpMessageConverter 与服务进行通信。

Spring MVC 中的 REST 支持

本部分提供了支持 RESTful web 服务的主要 Spring 功能(或注释)的概述。

@Controller
使用 @Controller 注释对将成为 MVC 中控制器的类进行注释并处理 HTTP 请求。
@RequestMapping
使用 @RequestMapping 注释对函数进行注释,该函数处理某些 HTTP 方法、URI 或 HTTP 头。此注释是 Spring REST 支持的关键。可以更改 method 参数以处理其他 HTTP 方法。
例如:

1
2
@RequestMapping(method=RequestMethod.GET, value=”/emps”,
headers=”Accept=application/xml, application/json”)
@PathVariable
使用 @PathVariable 注释可将 URI 中的路径变量作为参数插入。
例如:

SpingMVC中@Controller和@RestController的区别

官方文档:
@RestController is a stereotype annotation that combines @ResponseBody and @Controller.

简单点就是说@RestController就是一直返回json数据如果你配置了configureMessageConverters的话。

1)如果只是使用@RestController注解Controller,则Controller中的方法无法返回jsp页面,配置的视图解析器InternalResourceViewResolver不起作用,返回的内容就是Return 里的内容,如果是对象那么则返回json。

例如:本来应该到success.jsp页面的,则其显示success.

2)如果需要返回到指定页面,则需要用 @Controller配合视图解析器InternalResourceViewResolver才行。
3)如果需要返回JSON,XML或自定义mediaType内容到页面,则需要在对应的方法上加上@ResponseBody注解。

java实现文件合并的功能

package com.alanluo.recorder;


import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;


public class test2 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        List<String> list = new ArrayList<>();
        list.add("D:/1/jasndfjhamsfnaoihjsdfasd.tmp0");
        list.add("D:/1/jasndfjhamsfnaoihjsdfasd.tmp1");

        String targetPath = "D:/1/marge.pcm";


        FileInputStream in = null;
        FileOutputStream out = null;
        try {
            //新建一个目标文件对象
            File target = new File(targetPath);

            //实例化一个文件流输出对象
            out = new FileOutputStream(target);

            //循环读取要合并的文件集合
            for(String path:list) {

                //文件对象
                File file = new File(path);

                if (file.exists()) {

                    System.out.println("filePath:"+file.getAbsolutePath()+" file:"+file.length());

                    byte[] buf = new byte[1024];
                    int len = 0;
                    in = new FileInputStream(file);
                    while ((len = in.read(buf)) != -1) {
                        //写出数据
                        out.write(buf, 0, len);
                    }

                    if (in != null) {
                        in.close();
                    }
                }
            }


        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }


    }

   
}

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