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Java IO流学习总结之文件传输基础

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1、java io流总览

Java IO流学习总结之文件传输基础

2、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

3、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

4、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();
         }
     }
}

5、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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