Java IO流学习总结之文件传输基础

时间：2022-05-23 11:32:11

一、java io流总览

Java IO流学习总结之文件传输基础

二、file类

2.1 常用api

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package pkg1;
 
import java.io.file;
import java.io.ioexception;
 
/**
 * @author administrator
 * @date 2021/4/2
 */
public class filedemo {
    public static void main(string[] args) {
        // 了解构造函数，可查看api
        file file = new file("d:\\javaio\\cook");
        // 设置分隔符，不同系统也可以认识
        //file file=new file("d:"+file.separator);
 
        //system.out.println(file.exists());
        if (!file.exists()) {
            file.mkdirs();
        } else {
            file.delete();
        }
 
        //  是否是一个目录，如果是目录返回true,如果不是目录或目录不存在返回false
        system.out.println(file.isdirectory());
        // 如果是一个文件
        system.out.println(file.isfile());
 
        //file file2 = new file("d:\\javaio\\日记1.txt");
        file file2 = new file("d:\\javaio", "日记1.txt");
        if (!file2.exists()) {
            try {
                file2.createnewfile();
            } catch (ioexception e) {
                e.printstacktrace();
            }
        } else {
            file2.delete();
        }
 
        // 常用file对象的api
        system.out.println(file);// file.tostring()的内容
        system.out.println(file.getabsolutepath());
        system.out.println(file.getname());
        system.out.println(file2.getname());
        system.out.println(file.getparent());
        system.out.println(file2.getparent());
        system.out.println(file.getparentfile().getabsolutepath());
    }
}

测试结果：

Java IO流学习总结之文件传输基础

其他api：

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package pkg1;
 
import java.io.*;
import java.util.randomaccess;
 
/**
 * @author administrator
 * @date 2021/4/7
 */
class filedemo2 {
    public static void main(string[] args) {
        file file = new file("d:\\javaio\\example");
        if (!file.exists()) {
            file.mkdir();
        }
 
        /*string[] filenames = file.list(new filenamefilter() {
            @override
            public boolean accept(file dir, string name) {
                system.out.println("文件是："+dir + "\\" + name);
                return name.endswith("java");
            }
        });
        for (string filename : filenames != null ? filenames : new string[0]) {
            system.out.println(filename);
        }*/
 
        /*file[] files = file.listfiles(new filenamefilter() {
            @override
            public boolean accept(file dir, string name) {
                system.out.println("文件是：" + dir + "\\" + name);
                return false;
            }
        });
        for (file filename : files) {
            system.out.println(filename.tostring());
        }*/
 
        file[] files = file.listfiles(new filefilter() {
            @override
            public boolean accept(file pathname) {
                system.out.println(pathname);
                return false;
            }
        });
        for (file filename : files) {
            system.out.println(filename.tostring());
        }
 
    }
 
}

测试：

Java IO流学习总结之文件传输基础

2.2 遍历目录

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package pkg2;
 
import java.io.file;
 
/**
 * 列出file的一些常用操作，如过滤、遍历
 */
public class fileutils {
    /**
     * 列出指定目录（包括其子目录）下的所有文件
     */
    public static void listdirectory(file dir) throws illegalaccessexception {
        if (!dir.exists()) {
            throw new illegalargumentexception("目录:" + dir + "不存在");
        }
        if (!dir.isdirectory()) {
            throw new illegalargumentexception(dir + "不存在");
        }
 
        // list()用于列出当前目录下的子目录（不包含子目录下的内容）和文件。返回的是字符串数组。
        /*string[] filenames = dir.list();
        for (string string : filenames) {
            system.out.println(dir + "\\" + string);
        }*/
 
 
 
        // 若要遍历子目录下的内容，就要构造成file对象进行递归操作。file提供了直接返回file对象的api
        file[] files = dir.listfiles();//返回直接子目录（文件）的抽象
        /*for (file file : files) {
            system.out.println(file);
        }*/
        if (files != null && files.length > 0) {
            for (file file : files) {
                if (file.isdirectory()) {
                    // 递归
                    listdirectory(file);
                } else {
                    system.out.println(file);
                }
            }
        }
    }
}

测试类：

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package pkg2;
 
import java.io.file;
 
public class fileutilstest {
    public static void main(string[] args) throws illegalaccessexception {
        fileutils.listdirectory(new file("d:javaio"));
    }
}

测试结果：

Java IO流学习总结之文件传输基础

三、randomaccessfile类

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package pkg3;
 
import java.io.*;
import java.util.arrays;
 
public class rafdemo {
    public static void main(string[] args) throws ioexception {
        // 若没有指定路径，则表示相对路径，即项目所在路径。
        file demo = new file("demo");
        if (!demo.exists()) {
            demo.mkdir();
        }
 
        file file = new file(demo, "raf.dat");
        if (!file.exists()) {
            file.createnewfile();
        }
 
        randomaccessfile raf = new randomaccessfile(file, "rw");
        // 查看指针位置
        system.out.println(raf.getfilepointer());// 0
 
        raf.writeint('a');// 只写了一个字节
        system.out.println(raf.getfilepointer());
        raf.writeint('b');
 
        int i = 0x7fffffff;
        // 用write方法每次只能写一个字节，如果要把i写进去就要写4次
        raf.writeint(i >>> 24);//高8位
        raf.writeint(i >>> 16);
        raf.writeint(i >>> 8);
        raf.writeint(i);// 低8位
        system.out.println(raf.getfilepointer());
 
        // 直接写一个int ,与上述4步操作等效
        raf.writeint(i);
 
        string s = "中";
        byte[] gbk = s.getbytes("gbk");
        raf.write(gbk);
        system.out.println("raf长度：" + raf.length());
 
 
        // 读文件，必须把指针移到头部
        raf.seek(0);
        // 一次性读取，把文件中的内容都读到字节数组汇总
        byte[] buf = new byte[(int) raf.length()];
        raf.read(buf);
        system.out.println(arrays.tostring(buf));
        // 转为字符串
        /*string s1=new string(buf,"utf-8");
        system.out.println(s1);*/
        for (byte b : buf) {
            system.out.print(integer.tohexstring(b & 0xff) + " ");
        }
 
        raf.close();
    }
}

测试结果：

Java IO流学习总结之文件传输基础

四、字节流

4.1 fileinputstream

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package pkg4;
 
import java.io.*;
 
public class ioutil {
    /**
     * 读取指定文件内容， 按照十六进制输出到控制台，
     * 且每输出10个byte换行
     *
     * @param filename
     */
    public static void printhex(string filename) throws ioexception {
        // 把文件作为字节流进行操作
        fileinputstream fis = new fileinputstream(filename);
        int b;
        int i = 1;
 
        while ((b = fis.read()) != -1) {
            if (b <= 0xf) {
                // 单位数前补0
                system.out.print("0");
            }
 
            // 将整型b转换为16进制表示的字符串
            system.out.print(integer.tohexstring(b) + " ");
            if (i++ % 10 == 0) {
                system.out.println();
            }
        }
        fis.close();
    }
 
    public static void printhexbybytearray(string filename) throws ioexception {
        fileinputstream fis = new fileinputstream(filename);
        /*byte[] buf = new byte[20 * 1024];
        //从fis中批量读取字节，放入到buf字节数组中，从第0个位置开始放，最多放buf.length个，返回的是读到的字节个数
        int bytes = fis.read(buf, 0, buf.length);// 一次性读完，说明字节数组足够大
        int j = 1;
 
        for (int i = 0; i < bytes; i++) {
            if (buf[i] <= 0xf) {
                system.out.print("0");
            }
 
            system.out.println(integer.tohexstring(buf[i]) + " ");
 
            if (j++ % 10 == 0) {
                system.out.println();
            }
        }*/
 
        // 当字节数组容量不够，一次读不完时
        byte[] buf = new byte[8 * 1024];
        int bytes = 0;
        int j = 1;
        while ((bytes = fis.read(buf, 0, buf.length)) != -1) {
            for (int i = 0; i < bytes; i++) {
                // byte是8位，int类型是32位，为了避免数据转换错误，通过&0xff将高24位清零
                system.out.print(integer.tohexstring(buf[i] & 0xff) + " ");
                if (j++ % 10 == 0) {
                    system.out.println();
                }
            }
        }
 
        fis.close();
    }
 
    /**
     * 文件拷贝操作 -> 字节批量读取式拷贝，效率最优
     */
    public static void copyfile(file srcfile, file destfile) throws ioexception {
        if (!srcfile.exists()) {
            throw new illegalargumentexception("文件：" + srcfile + "不存在");
        }
        if (!srcfile.isfile()) {
            throw new illegalargumentexception(srcfile + "不是文件");
        }
 
        fileinputstream fis = new fileinputstream(srcfile);
        fileoutputstream fos = new fileoutputstream(destfile);
        byte[] buf = new byte[8 * 1024];
        int b;
        while ((b = fis.read(buf, 0, buf.length)) != -1) {
            fos.write(buf, 0, b);
            fos.flush();//最好加上这个
        }
        fis.close();
        fos.close();
    }
 
    /**
     * 用带缓冲的字节流，进行文件拷贝，效率居中
     */
    public static void copyfilebybuffer(file srcfile, file destfile) throws ioexception {
        if (!srcfile.exists()) {
            throw new illegalargumentexception("文件：" + srcfile + "不存在");
        }
        if (!srcfile.isfile()) {
            throw new illegalargumentexception(srcfile + "不是文件");
        }
 
        bufferedinputstream bis = new bufferedinputstream(new fileinputstream(srcfile));
        bufferedoutputstream bos = new bufferedoutputstream(new fileoutputstream(destfile));
        int c;
        while ((c = bis.read()) != -1) {
            bos.write(c);
            // 刷新缓冲区。不能省略，否则无法写入
            bos.flush();
        }
        bis.close();
        bos.close();
    }
 
    /**
     * 文件拷贝操作 -> 单字节，不带缓冲式拷贝，效率最差
     */
    public static void copyfilebybyte(file srcfile, file destfile) throws ioexception {
        if (!srcfile.exists()) {
            throw new illegalargumentexception("文件：" + srcfile + "不存在");
        }
        if (!srcfile.isfile()) {
            throw new illegalargumentexception(srcfile + "不是文件");
        }
 
        fileinputstream fis = new fileinputstream(srcfile);
        fileoutputstream fos = new fileoutputstream(destfile);
 
        int b;
        while ((b = fis.read()) != -1) {
            fos.write(b);
            fos.flush();
        }
        fis.close();
        fos.close();
    }
}

测试类：

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package pkg4;
 
import java.io.ioexception;
 
public class ioutiltest1 {
    public static void main(string[] args) {
        try {
            ioutil.printhex("d:\\javaio\\fileutils.java");
        } catch (ioexception e) {
            e.printstacktrace();
        }
    }
}

4.2 fileoutputstream

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package pkg5;
 
import pkg4.ioutil;
 
import java.io.filenotfoundexception;
import java.io.fileoutputstream;
import java.io.ioexception;
 
public class fileoutdemo {
    public static void main(string[] args) throws ioexception {
        // 如果该文件不存在，则直接创建，如果存在，则删除后创建。若要在后面追加内容，参数中加一个true
        fileoutputstream fos = new fileoutputstream("demo/out.dat");
        // 写入a的低8位
        fos.write('a');
        fos.write('b');
        // write只能写8位，那么写一个int需要4次，每次8位
        int a = 10;
        fos.write(a >>> 24);
        fos.write(a >>> 16);
        fos.write(a >>> 8);
        fos.write(a);
        byte[] gbk = "中国".getbytes("gbk");
        fos.write(gbk);
        fos.close();
 
        ioutil.printhex("demo/out.dat");
    }
}

测试类：

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package pkg5;
 
import pkg4.ioutil;
 
import java.io.datainputstream;
import java.io.dataoutputstream;
import java.io.file;
import java.io.ioexception;
 
public class ioutiltest3 {
    public static void main(string[] args) {
        try {
            ioutil.copyfile(new file("d:\\javaio\\abc.txt"), new file("d:\\javaio\\abc1.txt"));
        } catch (ioexception e) {
            e.printstacktrace();
        }
    }
}

4.3 datainputstream 、dataoutputstream

输入流：

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package pkg6;
 
import pkg4.ioutil;
 
import java.io.datainputstream;
import java.io.fileinputstream;
import java.io.ioexception;
 
public class disdemo {
    public static void main(string[] args) throws ioexception {
        string file = "demo/dos.dat";
        ioutil.printhex(file);
 
        datainputstream dis = new datainputstream(new fileinputstream(file));
        int i = dis.readint();
        system.out.println(i);
 
        i = dis.readint();
        system.out.println(i);
 
        long l = dis.readlong();
        system.out.println(l);
 
        double d = dis.readdouble();
        system.out.println(d);
 
        string s = dis.readutf();
        system.out.println(s);
 
        dis.close();
    }
}

输出流：

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package pkg6;
 
import pkg4.ioutil;
 
import java.io.dataoutputstream;
import java.io.filenotfoundexception;
import java.io.fileoutputstream;
import java.io.ioexception;
 
public class dosdemo {
    public static void main(string[] args) throws ioexception {
        string file = "demo/dos.dat";
        dataoutputstream dos = new dataoutputstream(new fileoutputstream(file));
        dos.writeint(10);
        dos.writeint(-10);
        dos.writelong(10l);
        dos.writedouble(10.5);
        // 采用utf-8写入
        dos.writeutf("中国");
        // 采用utf-16be写入
        dos.writechars("中国");
 
        dos.close();
        ioutil.printhex(file);
    }
}

4.4 字节缓冲流

工具类在4.1小节的ioutil.java中。

测试类：

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package pkg7;
 
import pkg4.ioutil;
 
import java.io.file;
import java.io.ioexception;
 
public class ioutiltest4 {
    public static void main(string[] args) {
        // 效率最高
        try {
            long start = system.currenttimemillis();
            ioutil.copyfile(new file("d:\\javaio\\alpha.mp3"), new file("d:\\javaio\\alpha1.mp3"));
            long end = system.currenttimemillis();
            system.out.println("耗时1：" + (end - start));
        } catch (ioexception e) {
            e.printstacktrace();
        }
 
        // 效率居中
        try {
            long start = system.currenttimemillis();
            ioutil.copyfilebybuffer(new file("d:\\javaio\\alpha.mp3"), new file("d:\\javaio\\alpha2.mp3"));
            long end = system.currenttimemillis();
            system.out.println("耗时2：" + (end - start));
        } catch (ioexception e) {
            e.printstacktrace();
        }
 
        // 效率最差
        try {
            long start = system.currenttimemillis();
            ioutil.copyfilebybyte(new file("d:\\javaio\\alpha.mp3"), new file("d:\\javaio\\alpha3.mp3"));
            long end = system.currenttimemillis();
            system.out.println("耗时3：" + (end - start));
        } catch (ioexception e) {
            e.printstacktrace();
        }
    }
}

五、字符流

5.1 inputstreamreader、outputstreamwriter

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package pkg8;
 
import java.io.*;
 
public class israndoswdemo {
    public static void main(string[] args) throws ioexception {
        fileinputstream fis = new fileinputstream("d:\\javaio\\aa.txt");
        inputstreamreader isr = new inputstreamreader(fis);//未指定编码格式，即按照项目默认编码操作
 
        fileoutputstream fos = new fileoutputstream("d:\\javaio\\aa.txt");
        outputstreamwriter osw = new outputstreamwriter(fos);//未指定编码格式，即按照项目默认编码操作
 
        /*int c;
        while ((c=isr.read())!=-1){
            system.out.print((char)c);
        }*/
 
        /*
        批量读取。
        放入buffer这个字节数组，从第0个位置开始放，最多放buffer.length个,返回读到的字符个数。
         */
        char[] buffer = new char[8 * 1024];
        int c;
        while ((c = isr.read(buffer, 0, buffer.length)) != -1) {
            string s = new string(buffer, 0, c);
            system.out.print(s);
 
            /*osw.write(buffer,0,c);
            osw.flush();*/
        }
 
        isr.close();
        osw.close();
    }
}

5.2 filereader、filewriter

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package pkg8;
 
import java.io.filenotfoundexception;
import java.io.filereader;
import java.io.filewriter;
import java.io.ioexception;
 
public class frandfwdemo {
    /**
     * 注意：filereader、filewriter不能指定编码方式
     */
    public static void main(string[] args) throws ioexception {
        filereader fr = new filereader("d:\\javaio\\aa.txt");
        // 指定参数，也可以追加内容：filewriter(string filename, boolean append)
        filewriter fw = new filewriter("d:\\javaio\\bb.txt");
        char[] buffer = new char[8 * 1024];
        int c;
        while ((c = fr.read(buffer, 0, buffer.length)) != -1) {
            fw.write(buffer, 0, c);
            fw.flush();
        }
        fr.close();
        fw.close();
    }
}

5.3 bufferedreader、bufferedwriter、printwriter

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package pkg9;
 
import java.io.*;
 
public class brandbworpwdemo {
    public static void main(string[] args) throws ioexception {
        // 对文件进行读写操作
        bufferedreader br = new bufferedreader(new inputstreamreader(new fileinputstream("d:\\javaio\\aa.txt")));
        //bufferedwriter bw = new bufferedwriter(new outputstreamwriter(new fileoutputstream("d:\\javaio\\cc.txt")));
        // printwriter可以替换bufferedwriter
        printwriter pw = new printwriter("d:\\javaio\\cc.txt");
 
        string line;
        while ((line = br.readline()) != null) {
            // 一次读一行，不能识别换行
            system.out.println(line);
            /*bw.write(line);
            // 手动给出换行
            bw.newline();
            bw.flush();*/
            pw.println(line);
            pw.flush();
        }
        br.close();
        //bw.close();
        pw.close();
    }
}

6、对象的序列化、反序列化

6.1 transient关键字、序列化、反序列化

实体类：

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package pkg10;
 
import java.io.serializable;
 
public class student implements serializable {
    private string stuno;
    private string stuname;
    // 该元素不会 进行jvm默认的序列化，但可以手动序列化
    private transient int stuage;
 
    public student(string stuno, string stuname, int stuage) {
        this.stuno = stuno;
        this.stuname = stuname;
        this.stuage = stuage;
    }
 
    public string getstuno() {
        return stuno;
    }
 
    public void setstuno(string stuno) {
        this.stuno = stuno;
    }
 
    public string getstuname() {
        return stuname;
    }
 
    public void setstuname(string stuname) {
        this.stuname = stuname;
    }
 
    public int getstuage() {
        return stuage;
    }
 
    public void setstuage(int stuage) {
        this.stuage = stuage;
    }
 
    @override
    public string tostring() {
        return "student{" +
                "stuno='" + stuno + '\'' +
                ", stuname='" + stuname + '\'' +
                ", stuage=" + stuage +
                '}';
    }
 
    /**
     * 序列化
     */
    private void writeobject(java.io.objectoutputstream s) throws java.io.ioexception {
        // 把jvm能默认序列化的元素进行序列化操作
        s.defaultwriteobject();
        // 手动完成stuage的序列化
        s.writeint(stuage);
    }
 
    /**
     * 反序列化
     */
    private void readobject(java.io.objectinputstream s) throws java.io.ioexception, classnotfoundexception {
        // 把jvm默认能反序列化的元素进行反序列化操作
        s.defaultreadobject();
        // 手动完成stuage的反序列化
        stuage = s.readint();
    }
}

测试类：

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package pkg10;
 
import java.io.*;
import java.util.arraylist;
 
public class objectseriademo {
    public static void main(string[] args) throws ioexception, classnotfoundexception {
        string file = "demo/obj.dat";
        // 1、对象的序列化
        /*objectoutputstream oos = new objectoutputstream(new fileoutputstream(file));
        student student = new student("10001", "张三", 20);
        oos.writeobject(student);
        oos.flush();
        oos.close();*/
        // 2、对象的反序列化
        objectinputstream ois = new objectinputstream(new fileinputstream(file));
        student stu = (student) ois.readobject();
        system.out.println(stu);
        ois.close();
    }
 
}

6.2 序列化、反序列化时，子类、父类构造方法的调用

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package pkg11;
 
import java.io.*;
import java.sql.sqloutput;
 
public class objectseriademo {
    public static void main(string[] args) throws ioexception, classnotfoundexception {
        // 序列化
        /*objectoutputstream oos=new objectoutputstream(new fileoutputstream("demo/obj1.dat"));
        foo2 foo2=new foo2();
        oos.writeobject(foo2);
        oos.flush();
        oos.close();*/
 
        // 反序列化
        /*objectinputstream ois=new objectinputstream(new fileinputstream("demo/obj1.dat"));
        foo2 foo2= (foo2) ois.readobject();
        system.out.println(foo2);
        ois.close();*/
 
 
 
        /*objectoutputstream oos=new objectoutputstream(new fileoutputstream("demo/obj1.dat"));
        bar2 bar2=new bar2();
        oos.writeobject(bar2);
        oos.flush();
        oos.close();*/
 
        /*objectinputstream ois = new objectinputstream(new fileinputstream("demo/obj1.dat"));
        bar2 bar2 = (bar2) ois.readobject();
        system.out.println(bar2);
        ois.close();*/
 
 
 
        /*objectoutputstream oos=new objectoutputstream(new fileoutputstream("demo/obj1.dat"));
        ccc2 ccc2=new ccc2();
        oos.writeobject(ccc2);
        oos.flush();
        oos.close();*/
 
        objectinputstream ois = new objectinputstream(new fileinputstream("demo/obj1.dat"));
        ccc2 ccc2 = (ccc2) ois.readobject();
        system.out.println(ccc2);
        ois.close();
    }
}
 
/**
 * 一个类实现了序列化接口，其子类都可以实现序列化。
 */
class foo implements serializable {
    public foo() {
        system.out.println("foo...");
    }
}
 
class foo1 extends foo {
    public foo1() {
        system.out.println("foo1...");
    }
}
 
class foo2 extends foo1 {
    public foo2() {
        system.out.println("foo2...");
    }
}
 
 
 
/**
 * 对子类对象进行反序列化操作时，
 * 如果其父类没有实现序列化接口
 * 那么其父类的构造函数会被调用
 */
class bar {
    public bar() {
        system.out.println("bar...");
    }
}
 
class bar1 extends bar implements serializable {
    public bar1() {
        system.out.println("bar1...");
    }
}
 
class bar2 extends bar1 {
    public bar2() {
        system.out.println("bar2...");
    }
}
 
 
 
class ccc {
    public ccc() {
        system.out.println("ccc...");
    }
}
 
class ccc1 extends ccc {
    public ccc1() {
        system.out.println("ccc1...");
    }
}
 
class ccc2 extends ccc1 implements serializable {
    public ccc2() {
        system.out.println("ccc2...");
    }
}

foo2类反序列化时不打印构造方法：

Java IO流学习总结之文件传输基础

bar2类反序列化时打印了bar的构造方法：

Java IO流学习总结之文件传输基础

ccc2类反序列化时打印了ccc、ccc1的构造方法：

Java IO流学习总结之文件传输基础

结论（详见导图标红部分）：

对子类对象进行反序列化操作时，如果其父类没有实现序列化接口，那么其父类的构造函数会被调用。

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原文链接：https://blog.csdn.net/ykmeory/article/details/115682087

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