0. 字节流与二进制文件
我的代码
package javalearn;
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 = "d:\\student.data";
/* 将Student对象写入二进制文件student.data */
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");
}
/* 从student.data中读取学生信息并组装成对象 */
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
- 1.二进制文件与文本文件的区别:二进制文件可以储存基本数据类型的变量;文本文件只能储存基本数据类型中的char类型变量。
- 2.如何优雅的关掉文件:
可以直接在try后面加一个括号，在括号中定义最后要关闭的资源。这样，不需要在catch后面加上finally，程序运行结束之后资源会自动关闭。
1. 字符流与文本文件
我的代码
- 使用BufferedReader从编码为UTF-8的文本文件中读出学生信息，并组装成对象然后输出。
package test;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
public class Main {
public static void main(String[] args) {
String fileName="d:/Students.txt";
List<Student> studentList = new ArrayList<>();
try(
FileInputStream fis=new FileInputStream(fileName);
InputStreamReader isr=new InputStreamReader(fis, "UTF-8");
BufferedReader br=new BufferedReader(isr))
{
String line=null;
while((line=br.readLine())!=null)
{
String[] msg=line.split("\\s+");
int id=Integer.parseInt(msg[0]);
String name=msg[1];
int age=Integer.parseInt(msg[2]);
double grade=Double.parseDouble(msg[3]);
Student stu=new Student(id,name,age,grade);
studentList.add(stu);
}
}
catch (FileNotFoundException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(studentList);
}
}
- 编写public static ListreadStudents(String fileName);从fileName指定的文本文件中读取所有学生，并将其放入到一个List中
public static List<Student> readStudents(String fileName)
{
List<Student> stuList = new ArrayList<>();
try(
FileInputStream fis=new FileInputStream(fileName);
InputStreamReader isr=new InputStreamReader(fis, "UTF-8");
BufferedReader br=new BufferedReader(isr))
{
String line=null;
while((line=br.readLine())!=null)
{
String[] msg=line.split("\\s+");
int id=Integer.parseInt(msg[0]);
String name=msg[1];
int age=Integer.parseInt(msg[2]);
double grade=Double.parseDouble(msg[3]);
Student stu=new Student(id,name,age,grade);
stuList.add(stu);
}
}
catch (FileNotFoundException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
return stuList;
}
- 使用PrintWriter将Student对象写入文本文件
package test;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
public class WriteFile {
public static void main(String[] args) {
// TODO Auto-generated method stub
String fileName = "d:/Students.txt";
try (FileOutputStream fos = new FileOutputStream(fileName, true);
OutputStreamWriter osw = new OutputStreamWriter(fos, "UTF-8");
PrintWriter pw = new PrintWriter(osw)) {
pw.println("1 zhang 18 85");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
- 使用ObjectInputStream/ObjectOutputStream读写学生对象。
package test;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class WriteFile {
public static void main(String[] args) {
// TODO Auto-generated method stub
String fileName="d:/Students.dat";
try(
FileOutputStream fos=new FileOutputStream(fileName);
ObjectOutputStream oos=new ObjectOutputStream(fos))
{
Student ts=new Student(1,"lily",64,90);
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();
}
}
}
2. 缓冲流(结合使用JUint进行测试)
我的代码
main函数：
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;
import javax.swing.text.AbstractDocument.BranchElement;
public class WriteFile {
public static void main(String[] args) {
// TODO Auto-generated method stub
String fileName = "e:/bigdata.txt";
int n = 1000_0000;
Random r = new Random(100); //把种子放在外面
try (PrintWriter pWriter = new PrintWriter(fileName)){ //省去finally
for (int i = 0; i < n; i++) {
pWriter.println(r.nextInt(11)); //产生0~10的随机数
}
} catch (FileNotFoundException e) {
// TODO: handle exception
e.printStackTrace();
}
/*try (BufferedReader br = new BufferedReader(new FileReader(new File(fileName)))){
String string = null;
int count=0;
long sum=0;
double average = 0.0;
while ((string=br.readLine())!=null) {
int num = Integer.parseInt(string);
sum+=num;
count++;
}
average=1.0*sum/count;
System.out.format("count = %d,sum = %d,averge = %.5f",count,sum,average);
} catch (FileNotFoundException e) {
// TODO: handle exception
e.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}*/
}
}
Junit：
package test;
import static org.junit.jupiter.api.Assertions.*;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;
import org.junit.jupiter.api.Test;
class testRead {
String fileName = "e:/bigdata.txt";
@Test
void testB() {
try (BufferedReader br = new BufferedReader(new FileReader(new File(fileName)))){
String string = null;
int count=0;
long sum=0;
double average = 0.0;
while ((string=br.readLine())!=null) {
int num = Integer.parseInt(string);
sum+=num;
count++;
}
average=1.0*sum/count;
System.out.format("count = %d,sum = %d,averge = %.5f",count,sum,average);
} catch (FileNotFoundException e) {
// TODO: handle exception
e.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
@Test
void testS() {
try (Scanner sc = new Scanner(new File(fileName))){
String string = null;
int count=0;
long sum=0;
double average = 0.0;
while (sc.hasNextLine()) {
string = sc.nextLine();
int num = Integer.parseInt(string);
sum+=num;
count++;
}
average=1.0*sum/count;
System.out.format("count = %d,sum = %d,averge = %.5f",count,sum,average);
} catch (FileNotFoundException e) {
// TODO: handle exception
e.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
我的总结
- 1.在产生随机数[0.10]时。先写成了r.nextInt(10)，这样只能生成[0,9]的随机数，应改为r.nextInt(11).
- 2.随机数种子应放在循环之外。
- 3.使用BufferedReader与使用Scanner从该文件中读取数据，明显使用Scanner读取文件慢的非常多。
- 4.注意格式化输出应用：System.out.format
3.字节流之对象流
我的代码
public static void writeStudent(List<Student> stuList)
{
String fileName="D:\\Student.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;
}
5.文件操作
我的代码
public class Main {
public static void main(String[] args) {
if (args.length == 0)
args = new String[] { ".." };
try {
File pathName = new File(args[0]);
String[] fileNames = pathName.list();
// enumerate all files in the directory
for (int i = 0; i < fileNames.length; i++) {
File f = new File(pathName.getPath(), fileNames[i]);
// if the file is again a directory, call the main method recursively
if (f.isDirectory()) {
if (f.getName().contains(fileName)) {
System.out.println(f.getCanonicalPath());
main(new String[] { f.getPath() });
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
我的总结
用了参考代码稍加修改，若文件名字包含fileName，则输出该文件的路径
