• 热门专题

JAVA多线程读取文件

作者:kaobian  发布日期:2011-07-18 19:21:32
Tag标签:多线程  读取  文件  
  • 原文来自:kaobian.iteye.com/blog

    单线程读取10K个 文件的话会显的非常的慢,但是如果我们开启多个线程去读取,会让读取的速度大大的加快,顺便说一下多线程的注意事项:synchronized 代码快中 尽量简短,不要有 类似socket.accept() inputstream.read() 这样的阻塞式的方法,这样会让程序减慢,如果synchronized代码快中的东西太多,容易造成单线程的囧地,而且速度还不如单线程快。

    废话少说,我们来看看代码:

    1.生成10K个 文件:

    package com.fileThread;
    
    import java.io.File;
    import java.io.FileOutputStream;
    import java.io.OutputStream;
    
    public class GenFile {
    
        /**
         * @param args
         * @throws Exception
         */
        public static void main(String[] args) throws Exception {
    
            File file = null;
            OutputStream out = null;
    
            file = new File("c:/file");
            if(!file.exists()){
                file.mkdirs();
            }
            for (int i = 0; i < 10000; i++) {
                file = new File("c:/file/file" + i + ".txt");
                out = new FileOutputStream(file);
                out.write("nihao1hh1hh1".getBytes());
                out.close();
            }
            file = null;
            out = null;
        }
    
    }
    ------------------------多线程 读取
    
    package com.fileThread;
    
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.IOException;
    import java.io.InputStream;
    
    public class ReadFile {
    
        public static void main(String[] args) throws Exception {
            Sum sum = new Sum();
            Thread t1 = new Thread(sum);
            Thread t2 = new Thread(sum);
            Thread t3 = new Thread(sum);
            t1.start();
            t2.start();
            t3.start();
            // t1.run();
            // t2.run();
            // t3.run();
            // System.out.println(sum.getSum()+"==");
        }
    }
    
    class Sum implements Runnable {
        private Integer i = 0;
        private Integer sum = 0;
        static long time;
    
        public void run() {
            File file = null;
            InputStream is = null;
            StringBuffer sb = null;
            while (true) {
                if (i == 0) {
                    time = System.currentTimeMillis();
                }
                if (i == 10000) {
                    break;
                }
                synchronized (this) {
                    file = new File("c:/file/file" + i + ".txt");
                    // System.out.println(i + "currentThread==" +
                    // Thread.currentThread().getName()); 
    
                  i++;
    
    
                }
               
                try {
                    is = new FileInputStream(file);
                } catch (FileNotFoundException e) {
                }
                byte[] data = new byte[2048];
                int len = 0;
                sb = new StringBuffer();
                try {
                    while ((len = is.read(data)) != -1) {
                        sb.append(new String(data, 0, len));
                    }
                } catch (IOException e) {
                }
                String result = sb.toString();
                String[] arr = result.split("\\D+");
                synchronized (this) {
                    for (String s : arr) {
                        if (s != null && s.trim().length() > 0) {
                            sum += Integer.parseInt(s);
                        }
                    }
                }
            }
            file = null;
            sb = null;
            is = null;
            System.out.println(this.sum);
            System.out.println(System.currentTimeMillis() - time);
        }
    
        public Integer getI() {
            return i;
        }
    
        public void setI(Integer i) {
            this.i = i;
        }
    
        public Integer getSum() {
            return sum;
        }
    
        public void setSum(Integer sum) {
            this.sum = sum;
        }
    
    }
    -------------------------所有的东西 都放到 synchronazied代码快中的速度比较,这个类似单线程
    
     
    
    package com.fileThread;
    
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.IOException;
    import java.io.InputStream;
    
    public class ReadFileAll {
    
        public static void main(String[] args) throws Exception {
            Sums sum = new Sums();
            Thread t1 = new Thread(sum);
            Thread t2 = new Thread(sum);
            Thread t3 = new Thread(sum);
            t1.start();
            t2.start();
            t3.start();
            // 22562
            // 14625
        }
    }
    
    class Sums implements Runnable {
        private Integer i = 0;
        private Integer sum = 0;
        static long time;
    
        public void run() {
            File file = null;
            InputStream is = null;
            StringBuffer sb = null;
            while (true) {
                if (i == 0) {
                    time = System.currentTimeMillis();
                }
                if (i == 10000) {
                    break;
                }
                synchronized (this) {
                    file = new File("c:/file/file" + i + ".txt");
    //                System.out.println(i + "currentThread=="
    //                        + Thread.currentThread().getName());
                    i++;
                    try {
                        is = new FileInputStream(file);
                    } catch (FileNotFoundException e) {
                    }
                    byte[] data = new byte[2048];
                    int len = 0;
                    sb = new StringBuffer();
                    try {
                        while ((len = is.read(data)) != -1) {
                            sb.append(new String(data, 0, len));
                        }
                    } catch (IOException e) {
                    }
                    String result = sb.toString();
                    String[] arr = result.split("\\D+");
                    for (String s : arr) {
                        if (s != null && s.trim().length() > 0) {
                            sum += Integer.parseInt(s);
                        }
                    }
                }
            }
            file = null;
            sb = null;
            is = null;
            System.out.println(this.sum);
            System.out.println(System.currentTimeMillis() - time);
        }
    
        public Integer getI() {
            return i;
        }
    
        public void setI(Integer i) {
            this.i = i;
        }
    
        public Integer getSum() {
            return sum;
        }
    
        public void setSum(Integer sum) {
            this.sum = sum;
        }
    
    }
    
    -------------------------------单线程去读的速度:
    
    package com.fileThread;
    
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.IOException;
    import java.io.InputStream;
    
    public class ReadFileSingleThread {
    
        public static void main(String[] args) throws Exception {
            int i = 0;
            long time = 0;
            int sum =0;
            File file = null;
            InputStream is = null;
            StringBuffer sb = null;
            while (true) {
                if (i == 0) {
                    time = System.currentTimeMillis();
                }
                if (i == 10000) {
                    break;
                }
                file = new File("c:/file/file" + i + ".txt");
                i++;
                try {
                    is = new FileInputStream(file);
                } catch (FileNotFoundException e) {
                }
                byte[] data = new byte[2048];
                int len = 0;
                sb = new StringBuffer();
                try {
                    while ((len = is.read(data)) != -1) {
                        sb.append(new String(data, 0, len));
                    }
                } catch (IOException e) {
                }
                String result = sb.toString();
                String[] arr = result.split("\\D+");
                for (String s : arr) {
                    if (s != null && s.trim().length() > 0) {
                        sum += Integer.parseInt(s);
                    }
                }
            }
            file = null;
            sb = null;
            is = null;
            System.out.println(sum);
            System.out.println(System.currentTimeMillis() - time);
        }
    }
    
    

    通过比较,大家就可以发现多线程的好处了,可能大家多如何写多线程存在疑问,这里我想说的是多想想,你的多线程是想做什么,就像 这个 例子,我的多线程 就是想 每个人线程分担 不同的文件读取,再算总和,所以我要控制的同步资源就是文件的名称和总和,所以我就需要把这两个 属性 同步上,这样就可以。如何返回多线程执行完的结果呢,我个人认为这样做,是让其他线程在mian 之前完成,这样就可以达到效果,可以用thread.join()方法,这样在执行mian 之前就会先把多线程执行完,就可以的到结果。

     

About IT165 - 广告服务 - 隐私声明 - 版权申明 - 免责条款 - 网站地图 - 网友投稿 - 联系方式
本站内容来自于互联网,仅供用于网络技术学习,学习中请遵循相关法律法规