JAVA第09次实验（IO流）

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JAVA第09次实验（IO流）

0.字节流与二进制文件

我的代码

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;class Student {
private int id;
private String name;
private int age;
private double grade;
public Student(){ }
public Student(int id, String name, int age, double grade) {
this.id = id;
this.setName(name);
this.setAge(age);
this.setGrade(grade);
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
if (name.length()>10){
throw new IllegalArgumentException("name's length should <=10 "+name.length());
}
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
if (age<=0){
throw new IllegalArgumentException("age should >0 "+age);
}
this.age = age;
}
public double getGrade() {
return grade;
}
public void setGrade(double grade) {
if (grade<0 || grade >100){
throw new IllegalArgumentException("grade should be in [0,100] "+grade);
}
this.grade = grade;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + ", age=" + age + ", grade=" + grade + "]";
} }
public class Main {
public static void main(String[] args)
{ String fileName="f:/student.txt";
try(DataOutputStream dos=new DataOutputStream(new FileOutputStream(fileName)))
{
Student[] stu=new Student[3];
stu[0]=new Student(1,"zhangsan",19,65.0);
stu[1]=new Student(2,"lisi",19,75.0);
stu[2]=new Student(3,"wangwu",20,85.0);
for(Student stu1:stu) {
dos.writeInt(stu1.getId());
dos.writeUTF(stu1.getName());
dos.writeInt(stu1.getAge());
dos.writeDouble(stu1.getGrade());
} } catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("1");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("2");
}
try(DataInputStream dis=new DataInputStream(new FileInputStream(fileName)))
{
while(dis!=null) {
int id=dis.readInt();
String name=dis.readUTF();
int age=dis.readInt();
double grade=dis.readDouble();
Student stu=new Student(id,name,age,grade);
System.out.println(stu);
} } catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("3");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("4");
}
}
}


我的总结

使用字节流读写文本文件用FileInputStream和FileOutputStream,DataOutputStream是字节流与字符流之间的桥梁。


1.字符流与文本文件：使用PrintWriter(写),BufferedReader(读)

我的代码

• (1)

public class Main {
public static void main(String[] args) throws IOException
{
String FileName="f:/Students.txt";
BufferedReader br = null;
try {
br = new BufferedReader(new InputStreamReader(new FileInputStream(FileName),"UTF-8"));
String line = null;
while((line=br.readLine())!=null)
System.out.println(line);
} finally{
if (br!=null){
br.close();
}
}
} }


• (2)

public static void ListreadStudents(String fileName){
ArrayList<Student> StudentList=new ArrayList<Student>();
BufferedReader br = null;
try {
br = new BufferedReader(new InputStreamReader(new FileInputStream(fileName),"UTF-8"));
while(br!=null) {
String line=br.readLine();
String[] stu=line.split("\\s+");
int id=Integer.parseInt(stu[0]);
String name=stu[1];
int age=Integer.parseInt(stu[2]);
double grade=Double.parseDouble(stu[3]);
Student Stu=new Student(id,name,age,grade);
StudentList.add(Stu);
}
} finally{
if (br!=null){
br.close();
}
}
}


• (3)

String FileName="f:Students.txt";
PrintWriter pw=new PrintWriter(new OutputStreamWriter(new FileOutputStream(FileName,true),"UTF-8"));
pw.print("4 wanger 21 90");
pw.close();


• (4)

String FileName="f:\Students.dat";
try(
FileOutputStream fos=new FileOutputStream(FileName);
ObjectOutputStream oos=new ObjectOutputStream(fos))
{
Student ts=new Student(5,"asd",14,60);
oos.writeObject(ts);
}
catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try(
FileInputStream fis=new FileInputStream(FileName);
ObjectInputStream ois=new ObjectInputStream(fis))
{
Student newStudent =(Student)ois.readObject();
System.out.println(newStudent);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}


我的总结

(1)直接打开会出现乱码，所以在读取前要把模式改为“UTF-8”；
(2)BufferedReader类带有缓冲区，可以优先把一批数据读到缓冲区。所以后面的读取操作，是从缓冲区内获取，避免每次都是从数据 源读取数据进行字符编码转换。


2. 缓冲流(结合使用JUint进行测试)

我的代码

• PrintWriter

String FILENAME = "test.txt";
double sum=0,aver;
PrintWriter pw=null;
try {
pw = new PrintWriter(FILENAME);
for(int i = 0;i<10000000;i++){//写入1千万行
int r=new Random().nextInt(10);
sum+=r;
pw.println(r);
//System.out.println(r);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}finally{
pw.close();
}
aver=sum/10000000;
System.out.format("%.5f", aver);
}


• JUint

public class test {
@Test
public void test() {
String FILENAME = "test.txt";
long begin = System.currentTimeMillis();
Scanner scanner=null;
try {
scanner = new Scanner(new File(FILENAME));
while(scanner.hasNextLine()){//只是读出每一行，不做任何处理
scanner.nextLine();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}finally{
scanner.close();
}
long end = System.currentTimeMillis();
System.out.println("last "+(end-begin));
System.out.println("read using Scanner done");
}
@Test
public void Bufftest() {
String FILENAME = "test.txt";
long begin = System.currentTimeMillis();
BufferedReader br = null;
try {
br = new BufferedReader(new FileReader(new File(FILENAME)));
while(br.readLine()!=null){};//只是读出，不进行任何处理
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
long end = System.currentTimeMillis();
System.out.println("last "+(end-begin));
System.out.println("read using BufferedReader done");
}
}


我的总结

在处理大量数据时，使用缓冲流BufferedReader比Scanner明显快很多。


3. 字节流之对象流

我的代码

public static void writeStudent(List<Student> stuList)
{
String fileName="f:/Students.dat";
try ( FileOutputStream fos=new FileOutputStream(fileName);
ObjectOutputStream ois=new ObjectOutputStream(fos))
{
ois.writeObject(stuList); }
catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
public static List<Student> readStudents(String fileName)
{
List<Student> stuList=new ArrayList<>();
try ( FileInputStream fis=new FileInputStream(fileName);
ObjectInputStream ois=new ObjectInputStream(fis))
{
stuList=(List<Student>)ois.readObject();
}
catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return stuList;
}


我的总结

ObjectOutputStream、ObjectInputStream与FileInputStream、FileOuputStream放在一起使用时，可以对对象永久存储。其中ObjectOutputStream、ObjectInputStream是高级流。