所谓IO,也就是Input与Output的缩写。在java中,IO涉及的范围比较大,这里主要讨论针对文件内容的读写

其他知识点将放置后续章节(我想,文章太长了,谁都没耐心翻到最后)

 

对于文件内容的操作主要分为两大类

分别是:

  字符流

  字节流

其中,字符流有两个抽象类:Writer   Reader

其对应子类FileWriterFileReader可实现文件的读写操作

BufferedWriterBufferedReader能够提供缓冲区功能,用以提高效率

 

同样,字节流也有两个抽象类:InputStream   OutputStream

其对应子类有FileInputStreamFileOutputStream实现文件读写

BufferedInputStreamBufferedOutputStream提供缓冲区功能

 

俺当初学IO的时候犯了不少迷糊,网上有些代码也无法通过编译,甚至风格都很大不同,所以新手请注意:       

        1.本文代码较长,不该省略的都没省略,主要是因为作为一个新手需要养成良好的代码编写习惯

   2.本文在linux下编译,类似于File.pathSeparator和File.separator这种表示方法是出于跨平台性和健壮性考虑

   3.代码中有些操作有多种执行方式,我采用了方式1...方式2...的表述,只需轻轻解开注释便可编译

   4.代码中并没有在主方法上抛出异常,而是分别捕捉,造成代码过长,如果仅是测试,或者不想有好的编程习惯,那你就随便抛吧……

        5.功能类似的地方就没有重复写注释了,如果新手看不懂下面的代码,那肯定是上面的没有理解清楚

 

字符流

实例1:字符流的写入

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import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
 
public class Demo {
    public static void main(String[] args ) {
         
        //创建要操作的文件路径和名称
        //其中,File.separator表示系统相关的分隔符,Linux下为:/  Windows下为:\\
        String path = File.separator + "home" + File.separator + "siu" +
                      File.separator + "work" + File.separator + "demo.txt";
     
        //由于IO操作会抛出异常,因此在try语句块的外部定义FileWriter的引用
        FileWriter w = null;
        try {
            //以path为路径创建一个新的FileWriter对象
            //如果需要追加数据,而不是覆盖,则使用FileWriter(path,true)构造方法
            w = new FileWriter(path);
             
            //将字符串写入到流中,\r\n表示换行想有好的
            w.write("Nerxious is a good boy\r\n");
            //如果想马上看到写入效果,则需要调用w.flush()方法
            w.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //如果前面发生异常,那么是无法产生w对象的
            //因此要做出判断,以免发生空指针异常
            if(w != null) {
                try {
                    //关闭流资源,需要再次捕捉异常
                    w.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

编译之后,在目录下面生成文件,并写入字符串

 

实例2:字符流的读取

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import java.io.File;
import java.io.FileReader;
import java.io.IOException;
 
public class Demo2 {
    public static void main(String[] args ) {
        String path = File.separator + "home" + File.separator + "siu" +
                      File.separator + "work" + File.separator + "demo.txt";
 
        FileReader r = null;
        try {
            r = new FileReader(path);
             
            //方式一:读取单个字符的方式
            //每读取一次,向下移动一个字符单位
            int temp1 = r.read();
            System.out.println((char)temp1);
            int temp2 = r.read();
            System.out.println((char)temp2);
                         
            //方式二:循环读取
            //read()方法读到文件末尾会返回-1
            /*
            while (true) {
                int temp = r.read();
                if (temp == -1) {
                    break;
                }
                System.out.print((char)temp);
            }
            */
             
            //方式三:循环读取的简化操作
            //单个字符读取,当temp不等于-1的时候打印字符
            /*int temp = 0;
            while ((temp = r.read()) != -1) {
                System.out.print((char)temp);
            }
            */
             
            //方式四:读入到字符数组
            /*
            char[] buf = new char[1024];
            int temp = r.read(buf);
            //将数组转化为字符串打印,后面参数的意思是
            //如果字符数组未满,转化成字符串打印后尾部也许会出现其他字符
            //因此,读取的字符有多少个,就转化多少为字符串
            System.out.println(new String(buf,0,temp));
            */
             
            //方式五:读入到字符数组的优化
            //由于有时候文件太大,无法确定需要定义的数组大小
            //因此一般定义数组长度为1024,采用循环的方式读入
            /*
            char[] buf = new char[1024];
            int temp = 0;
            while((temp = r.read(buf)) != -1) {
                System.out.print(new String(buf,0,temp));
            }
            */
             
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(r != null) {
                try {
                    r.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

编译之后的效果:

 

实例3:文本文件的复制

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import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
 
public class Demo {
    public static void main(String[] args ) {
         
        String doc = File.separator + "home" + File.separator + "siu" +
                      File.separator + "work" + File.separator + "demo.txt";
         
        String copy = File.separator + "home" + File.separator + "siu" +
                     File.separator + "life" + File.separator + "lrc.txt";
 
        FileReader r = null;
        FileWriter w = null;
        try {
            r = new FileReader(doc);
            w = new FileWriter(copy);
             
            //方式一:单个字符写入
            int temp = 0;
            while((temp = r.read()) != -1) {
                w.write(temp);
            }
             
            //方式二:字符数组方式写入
            /*
            char[] buf = new char[1024];
            int temp = 0;
            while ((temp = r.read(buf)) != -1) {
                w.write(new String(buf,0,temp));
            }
            */
             
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //分别判断是否空指针引用,然后关闭流
            if(r != null) {
                try {
                    r.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(w != null) {
                try {
                    w.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

 编译之后,产生life目录下的lrc.txt文件,复制成功

 

实例4:利用字符流的缓冲区来进行文本文件的复制

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import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
 
public class Demo {
    public static void main(String[] args ) {
         
        String doc = File.separator + "home" + File.separator + "siu" +
                      File.separator + "work" + File.separator + "demo.txt";
         
        String copy = File.separator + "home" + File.separator + "siu" +
                     File.separator + "life" + File.separator + "lrc.txt";
 
        FileReader r = null;
        FileWriter w = null;
        //创建缓冲区的引用
        BufferedReader br = null;
        BufferedWriter bw = null;
        try {
            r = new FileReader(doc);
            w = new FileWriter(copy);
            //创建缓冲区对象
            //将需要提高效率的FileReader和FileWriter对象放入其构造函数内
            //当然,也可以使用匿名对象的方式 br = new BufferedReader(new FileReader(doc));
            br = new BufferedReader(r);
            bw = new BufferedWriter(w);
             
            String line = null;
            //读取行,直到返回null
            //readLine()方法只返回换行符之前的数据
            while((line = br.readLine()) != null) {
                //使用BufferWriter对象的写入方法
                bw.write(line);
                //写完文件内容之后换行
                //newLine()方法依据平台而定
                //windows下的换行是\r\n
                //Linux下则是\n
                bw.newLine();
            }      
             
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //此处不再需要捕捉FileReader和FileWriter对象的异常
            //关闭缓冲区就是关闭缓冲区中的流对象
            if(br != null) {
                try {
                    r.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(bw != null) {
                try {
                    bw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

 

字节流

实例5:字节流的写入

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import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
 
public class Demo {
    public static void main(String[] args ) {
          
        String path = File.separator + "home" + File.separator + "siu" +
                      File.separator + "work" + File.separator + "demo.txt";
         
        FileOutputStream o = null;
         
        try {
            o = new FileOutputStream(path);
            String str = "Nerxious is a good boy\r\n";
            byte[] buf = str.getBytes();
            //也可以直接使用o.write("String".getBytes());
            //因为字符串就是一个对象,能直接调用方法
            o.write(buf);
             
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(o != null) {
                try {
                    o.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    
    }
}

编译之后产生的文件,以上在字符串中加\r\n就是为了便于终端显示

其实在linux下面换行仅用\n即可

 

实例6:字节流的读取

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import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
 
public class Demo {
    public static void main(String[] args ) {
          
        String path = File.separator + "home" + File.separator + "siu" +
                      File.separator + "work" + File.separator + "demo.txt";
         
        FileInputStream i = null;
         
        try {
            i = new FileInputStream(path);
             
            //方式一:单个字符读取
            //需要注意的是,此处我用英文文本测试效果良好
            //但中文就悲剧了,不过下面两个方法效果良好
            int ch = 0;
            while((ch=i.read()) != -1){
                System.out.print((char)ch);
            }
             
            //方式二:数组循环读取
            /*
            byte[] buf = new byte[1024];
            int len = 0;
            while((len = i.read(buf)) != -1) {
                System.out.println(new String(buf,0,len));
            }
            */
             
             
            //方式三:标准大小的数组读取
            /*
            //定一个一个刚好大小的数组
            //available()方法返回文件的字节数
            //但是,如果文件过大,内存溢出,那就悲剧了
            //所以,亲们要慎用!!!上面那个方法就不错
            byte[] buf = new byte[i.available()];
            i.read(buf);
            //因为数组大小刚好,所以转换为字符串时无需在构造函数中设置起始点
            System.out.println(new String(buf));
            */
             
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(i != null) {
                try {
                    i.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    
    }
}

 读取文件到终端

 

实例7:二进制文件的复制

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import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
 
public class Demo {
    public static void main(String[] args ) {
          
        String bin = File.separator + "home" + File.separator + "siu" +
                      File.separator + "work" + File.separator + "一个人生活.mp3";
         
        String copy = File.separator + "home" + File.separator + "siu" +
                      File.separator + "life" + File.separator + "一个人生活.mp3";
         
        FileInputStream i = null;
        FileOutputStream o = null;
         
        try {
            i = new FileInputStream(bin);
            o = new FileOutputStream(copy);
             
            //循环的方式读入写出文件,从而完成复制
            byte[] buf = new byte[1024];
            int temp = 0;
            while((temp = i.read(buf)) != -1) {
                o.write(buf, 0, temp);
            }
 
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(i != null) {
                try {
                    i.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(o != null) {
                try {
                    o.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

 复制效果,如图:

 

 实例8:利用字节流的缓冲区进行二进制文件的复制

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import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
 
public class Demo {
    public static void main(String[] args ) {
          
        String bin = File.separator + "home" + File.separator + "siu" +
                      File.separator + "work" + File.separator + "一个人生活.mp3";
         
        String copy = File.separator + "home" + File.separator + "siu" +
                      File.separator + "life" + File.separator + "一个人生活.mp3";
         
        FileInputStream i = null;
        FileOutputStream o = null;
        BufferedInputStream bi = null;
        BufferedOutputStream bo = null;
         
        try {
            i = new FileInputStream(bin);
            o = new FileOutputStream(copy);
            bi = new BufferedInputStream(i);
            bo = new BufferedOutputStream(o);
             
            byte[] buf = new byte[1024];
            int temp = 0;
            while((temp = bi.read(buf)) != -1) {
                bo.write(buf,0,temp);
            }
             
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(bi != null) {
                try {
                    i.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(bo != null) {
                try {
                    o.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

 两个目录都有 “一个人生活.mp3”文件,顺便说一下,这歌挺好听的

 

初学者在学会使用字符流和字节流之后未免会产生疑问:什么时候该使用字符流,什么时候又该使用字节流呢?

其实仔细想想就应该知道,所谓字符流,肯定是用于操作类似文本文件或者带有字符文件的场合比较多

而字节流则是操作那些无法直接获取文本信息的二进制文件,比如图片,mp3,视频文件等

说白了在硬盘上都是以字节存储的,只不过字符流在操作文本上面更方便一点而已

此外,为什么要利用缓冲区呢?

我们知道,像迅雷等下载软件都有个缓存的功能,硬盘本身也有缓冲区

试想一下,如果一有数据,不论大小就开始读写,势必会给硬盘造成很大负担,它会感觉很不爽

人不也一样,一顿饭不让你一次吃完,每分钟喂一勺,你怎么想?

因此,采用缓冲区能够在读写大文件的时候有效提高效率

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