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IO

2022-08-03 20:03:25  阅读:69  来源: 互联网

标签:String System IO import new public out


IO

创建文件

package com.IO;

import org.junit.jupiter.api.Test;

import java.io.File;
import java.io.IOException;

//创建文件
public class FileCreate {
    public static void main(String[] args) {

    }

    //方式1、new File(String pathname)
    @Test
    public void create01() {
        String filepath = "D:\\JAVA_IO_news1.txt";
        File file = new File(filepath);

        try {
            file.createNewFile();
            System.out.println("文件创建成功");
        } catch (IOException e) {
            e.printStackTrace();
        }

    }


    //方式2、根据父目录文件 + 子路径构建:new File(File parent,String child)
    @Test
    public void create02() {
        File parentFile = new File("D:\\");
        String filename = "JAVA_IO_news2.txt";

        //这里的file对象只是java程序中的一个对象,并不是具体到磁盘上的文件
        File file = new File(parentFile, filename);

        try {
            file.createNewFile();//该操作将生成具体的磁盘上的文件
            System.out.println("第二种文件创建方式创建成功");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //方式3、根据父目录 + 子路径构建:new File(String parent,String child)
    @Test
    public void create03() {
        String parentPath = "D:\\";
        String filePath = "JAVA_IO_news3.txt";

        File file = new File(parentPath, filePath);

        try {
            file.createNewFile();
            System.out.println("第三种文件创建方式创建成功");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

获取文件信息

package com.IO;

import org.junit.jupiter.api.Test;

import java.io.File;
import java.io.IOException;

public class FileInformation {
    public static void main(String[] args) {

    }


    //获取文件信息
    @Test
    public void info() throws IOException {
        //先创建文件对象
        File file = new File("D:\\news1.txt");

        file.createNewFile();

        //调用相应的方法,得到对应信息
        //getName,getAbsolutePath,getParent,length,exists,isFile,isDirectory
        System.out.println("文件名字 = " + file.getName());
        System.out.println("文件绝对路径:"+file.getAbsoluteFile());
        System.out.println("getParent:"+file.getParent());
        System.out.println("length:"+file.length());//计算字节大小
        System.out.println("exists:"+file.exists());
        System.out.println("isFile:"+file.isFile());
        System.out.println("isDirectory:"+file.isDirectory());



    }
}

image

目录操作

package com.IO;

import org.junit.jupiter.api.Test;

import java.io.File;

public class Directory_ {
    public static void main(String[] args) {

    }

    //判断文件是否存在,存在则删除
    @Test
    public void m1() {

        String filePath = "D:\\news1.txt";

        File file = new File(filePath);
        if (file.exists()) {
            if (file.delete()) {
                System.out.println(filePath + "文件删除成功");
            } else {
                System.out.println(filePath + "文件删除失败");
            }
        } else {
            System.out.println(filePath + "文件不存在");
        }
    }


    //判断目录是否存在,存在则删除
    @Test
    public void m2() {
        String directoryPath = "D:\\demo02";

        File file = new File(directoryPath);


        if (file.exists()) {
            if (file.delete()) {
                System.out.println(directoryPath + "文件删除成功");
            } else {
                System.out.println(directoryPath + "文件删除失败");
            }
        } else {
            System.out.println(directoryPath + "文件不存在");
        }
    }

    //判断目录是否存在,不存在则创建
    @Test
    public void m3() {
        String directoryPath = "D:\\demo03";

        File file = new File(directoryPath);

        if (file.exists()) {
            System.out.println(directoryPath + "目录已存在");
        } else {
            if (file.mkdir()) {//多级目录要使用 mkdirs
                System.out.println(directoryPath + "目录创建成功");
            } else {
                System.out.println(directoryPath + "目录创建失败");
            }
        }
    }


}

InputStream

image

package com.IO.inputstream;

import org.junit.jupiter.api.Test;

import java.io.FileInputStream;
import java.io.IOException;

public class FileInputStream_ {
    public static void main(String[] args) {

    }


    //读取文件(字节流)read()方法
    @Test
    public void readFile01() {
        String filePath = "D:\\news01.txt";
        int readData = 0;
        FileInputStream fileInputStream = null;
        try {
            //FileInputStream用于读取文件
            fileInputStream = new FileInputStream(filePath);

            //fileInputStream.read():从该输入流读取一个字节的数据。如果没有输入可用,该方法将阻止
            //返回-1,表示读取完毕
            while ((readData = fileInputStream.read()) != -1) {
                System.out.print((char) readData);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭输入流
            try {
                fileInputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    //读取文件(字节流)read(byte[] b)方法
    @Test
    public void readFile02() {
        String filePath = "D:\\news01.txt";
        FileInputStream fileInputStream = null;
        int readLen = 0;
        //定义一个字节数组
        byte[] bytes = new byte[8];//一次读取8个字节
        try {
            //FileInputStream用于读取文件
            fileInputStream = new FileInputStream(filePath);
            //fileInputStream.read(byte[] b):从该输入流最多读取b.length长度的数据到字节数组
            //fileInputStream.read(byte[] b):返回实际读取的字节数
            //返回-1,表示读取完毕
            while ((readLen = (fileInputStream.read(bytes))) != -1) {
                System.out.print(new String(bytes, 0, readLen));
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭输入流
            try {
                fileInputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

OutputStream

image

package com.IO.OutputStream;

import org.junit.jupiter.api.Test;

import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutputStream_ {
    public static void main(String[] args) {

    }


    //数据写入到文件
    @Test
    public void writeFile() {

        //创建 FileOutputStream对象
        String filePath = "D:\\news02.txt";

        FileOutputStream fileOutputStream = null;

        try {

            //1、当使用new FileOutputStream(filePath)构造方式时,写入内容会覆盖原来的内容
            //2、使用new FileOutputStream(filePath,true)构造方式时,写入内容会追加到原来的内容后
            fileOutputStream = new FileOutputStream(filePath,true);
            //写入一个字节
            //fileOutputStream.write('H');

            //写入字符串
            //getBytes():将 字符串 转成 字节数组
            String str = "hello,world";
            fileOutputStream.write(str.getBytes());

            //write(byte b[], int off, int len)方法:只写入指定位置的数组
            fileOutputStream.write(str.getBytes(),0,str.length());

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                fileOutputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

文件拷贝操作

package com.IO;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileCopy {
    public static void main(String[] args) {

        //文件拷贝
        //先用输入流将文件写入,再用输出流将文件写出,完成文件的拷贝
        //news03.txt->news04.txt
        String srcFilePath = "D:\\微信截图.png";
        String DestFilePath = "D:\\test.png";
        FileInputStream fileInputStream = null;
        FileOutputStream fileOutputStream = null;

        try {
            fileInputStream = new FileInputStream(srcFilePath);
            fileOutputStream = new FileOutputStream(DestFilePath);

            //用数组来读取
            byte[] buf = new byte[1024];
            int readLen = 0;

            while ((readLen = fileInputStream.read(buf)) != -1) {
                //读取到源文件后,就写入到目标文件,边读边写

                fileOutputStream.write(buf, 0, buf.length);
            }
            System.out.println("文件拷贝成功");

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                fileInputStream.close();
                fileOutputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

文件字符流

image

image

FileReader

package com.IO.reader;

import org.junit.jupiter.api.Test;

import java.io.FileReader;
import java.io.IOException;

public class FileReader_ {
    public static void main(String[] args) {

        String filePath = "D:\\news03.txt";
        FileReader fileReader = null;
        int data = 0;

        //1、创建FileReader对象
        try {
            fileReader = new FileReader(filePath);
            //循环读取 使用read,单个字符读取
            while ((data = fileReader.read()) != -1) {
                System.out.print((char) data);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileReader != null) {
                try {
                    fileReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }


    //第二种方法
    @Test
    public void ReadFile02() {
        String filePath = "D:\\news03.txt";
        FileReader fileReader = null;
        int readLen = 0;
        char[] buf = new char[8];

        //1、创建FileReader对象
        try {
            fileReader = new FileReader(filePath);
            //循环读取 使用read(buf)返回读取到的字符数
            while ((readLen = fileReader.read(buf)) != -1) {
                System.out.print(new String(buf, 0, readLen));
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileReader != null) {
                try {
                    fileReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

FileWriter

package com.IO.Writer;

import java.io.FileWriter;
import java.io.IOException;

public class FileWriter_ {
    public static void main(String[] args) {
        String filePath = "D:\\news04.txt";

        FileWriter fileWriter = null;

        char[] chars = {'a', 'b', 'c', 'd'};

        try {
            fileWriter = new FileWriter(filePath, true);

            //1、write()方法:写入单个字符
            //fileWriter.write('H');

            //2、write(char[])方法:写入指定数组
            //fileWriter.write(chars);

            //3、write(char[],off,len)方法:写入指定数组的指定部分
            //fileWriter.write("北京欢迎你".toCharArray(), 0, 5);

            //4、write(String)方法:写入整个字符串
            //fileWriter.write("你好,深圳!");

            //5、write(String,off,len)方法:写入字符串的指定部分
            fileWriter.write("最美重庆,天下", 0, 4);
            
            //在数据量大的情况下,可以使用循环操作

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //对应fileWriter,一定要关闭流或者flush操作才能真正把数据写入到文件中去
            try {
                fileWriter.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

节点流和处理流

image

  1. 节点流:可以从一个特定的数据源读写数据,如FileReader,FileWriter,是底层流/低级流,直接和数据源相接
  2. 处理流:是连接在已经存在的流之上,位程序提供更为强大的读写功能,如BufferedReader,BufferedWriter
    1. 包装节点流,既可以消除不同节点流的实现差异,也可以提供更方便的方法完成输入输出
    2. 对节点流进行包装,使用了修饰器设计模式,不会直接与数据源相连
    3. 关闭的时候只需要关闭外层即可

模拟修饰器设计模式

package com.IO.decoratorDesignPatternTest;

public abstract class Reader_ {//抽象类
    public void readFile_() {
    }

    public void readString_() {
    }
}
package com.IO.decoratorDesignPatternTest;

public class FileReader_ extends Reader_ {
    public void readFile_() {
        System.out.println("对文件进行读取...");
    }
}
package com.IO.decoratorDesignPatternTest;

public class StringReader_ extends Reader_ {
    public void readString_(){
        System.out.println("读取字符串...");
    }
}
package com.IO.decoratorDesignPatternTest;


//处理流模拟
public class BufferedReader_ extends Reader_ {

    private Reader_ reader_;

    //接收Reader_子类对象
    public BufferedReader_(Reader_ reader_) {
        this.reader_ = reader_;
    }

    //多次读取文件
    public void readFiles(int num) {
        for (int i = 0; i < num; i++) {
            reader_.readFile_();
        }
    }

    public void readFile_(){
        reader_.readFile_();
    }

    //扩展readString,批量处理字符串数据
    public void readStrings(int num) {
        for (int i = 0; i < num; i++) {
            reader_.readString_();
        }
    }

    public void readString_(){
        reader_.readString_();
    }
}

测试结果:

package com.IO.decoratorDesignPatternTest;

public class Test_ {
    public static void main(String[] args) {

        BufferedReader_ bufferedReader_ = new BufferedReader_(new FileReader_());

        bufferedReader_.readFile_();

        BufferedReader_ bufferedReader_1 = new BufferedReader_(new StringReader_());

        bufferedReader_1.readStrings(5);

    }
}

image


BufferedReader

package com.IO.reader;

import java.io.BufferedReader;
import java.io.FileReader;

public class BufferedReader_ {
    public static void main(String[] args) throws Exception {

        String filePath = "D:\\news01.txt";

        BufferedReader bufferedReader = new BufferedReader(new FileReader(filePath));

        String line;

        //readLine()按行读取文件
        //返回值为空表示读取完文件
        while ((line = bufferedReader.readLine()) != null) {

            System.out.println(line);
        }

        //关闭流,只需要关闭外层,就是bufferedReader,底层会自动去关闭FileReader节点流
        bufferedReader.close();
    }
}

BufferedWriter

package com.IO.writer;

import java.io.BufferedWriter;
import java.io.FileWriter;

public class BufferedWriter_ {
    public static void main(String[] args) throws Exception{
        String filePath = "D:\\news02.txt";

        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(filePath,true));

        bufferedWriter.write("BufferedWriter写入测试!!!");
        bufferedWriter.write("BufferedWriter写入测试!!!");

        bufferedWriter.newLine();//插入一个和系统相关的换行

        bufferedWriter.write("BufferedWriter写入测试!!!");
        bufferedWriter.write("BufferedWriter写入测试!!!");
        bufferedWriter.write("BufferedWriter写入测试!!!");

        bufferedWriter.close();
    }
}

image


Buffered拷贝

package com.IO;

import java.io.*;

public class BufferedCopy_ {
    public static void main(String[] args) {
        
        //BufferedReader、BufferedWriter是按照字符操作的,不要去操作二进制文件,可能会造成文件损坏(声音、视频、PDF,WORD文档)
        String srcFilePath = "D:\\news01.txt";
        String destFilePath = "D:\\news01_copyHere.txt";

        BufferedReader br = null;
        BufferedWriter bw = null;
        String line;

        try {
            br = new BufferedReader(new FileReader(srcFilePath));
            bw = new BufferedWriter(new FileWriter(destFilePath));

            while ((line = br.readLine()) != null) {
                //读一行写一行
                bw.write(line);
                //插入换行
                bw.newLine();
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭流
            try {
                if (br != null) {
                    br.close();
                }
                if (bw != null) {
                    bw.close();
                }
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

字节流拷贝文件

package com.IO.outputStream;

import java.io.*;

//字节处理流(包装流拷贝文件)
//可以操作二进制文件
public class BufferedCopy02 {
    public static void main(String[] args) {
        
        String srcFilePath = "D:\\news01.txt";
        String destFilePath = "D:\\mews01_BufferedCopy02_CopyHere.txt";

        //创建BufferedInputStream对象、BufferedOutputStream对象
        BufferedInputStream bis = null;
        BufferedOutputStream bos = null;

        try {
            bis = new BufferedInputStream(new FileInputStream(srcFilePath));
            bos = new BufferedOutputStream(new FileOutputStream(destFilePath));

            //循环读取文件,并写入到destFilePath
            byte[] buff = new byte[1024];
            int readLen = 0;

            while ((readLen = bis.read(buff)) != -1) {
                bos.write(buff, 0, buff.length);
            }
            System.out.println("文件拷贝成功");

        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            //关闭流
            if (bis!=null){
                try {
                    bis.close();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            if (bos!=null){
                try {
                    bos.close();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }
    }
}

对象处理流

对象流:ObjectInputStream和ObjectOutputStream

能够将基本数据类型或者对象进行序列化和反序列化的操作

  • 序列化:保存数据时,保存数据的值和数据类型
  • 反序列化:恢复数据时,恢复数据的值和数据类型
  • 要想让某个对象支持序列化机制,则其类必须是可序列化的,那么该类必须实现如下两个接口之一:
    • Serializable //标记接口,没有方法
    • Externalizable
  • 注意事项和细节:
    • 序列化和反序列化的读写顺序要一致
    • 对象需要实现Serializable
    • 序列化的类中建议添加SerializableUID,提高版本的兼容性
    • 序列化对象时,默认将里面的所有属性都序列化,但除了static和transient修饰的成员
    • 序列化对象时,要求里面的属性也需要实现序列化接口
    • 序列化具备可继承性,也就是如果某类已经实现了序列化,则他的所有子类默认实现了序列化

ObjectOutputStream 和 ObjectInputStream

package com.IO.outputStream;

import java.io.Serializable;

//要序列化某个类的对象,这个类就要实现Serializable
public class Dog implements Serializable {
    private String name;
    private int age;

    //SerializableUID 序列化的版本号,可以提高兼容性

    public Dog(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Dog{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}
package com.IO.outputStream;

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;

public class ObjectOutputStream_ {
    public static void main(String[] args) throws Exception {
        //序列化后,保存的文件格式,不是文本,而是按照他的格式来保存

        String filePath = "D:\\news05.txt";

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(filePath));

        //序列化数据到:D:\news05.txt
        oos.writeInt(100);
        oos.writeBoolean(true);
        oos.writeChar('c');
        oos.writeDouble(11.13);
        oos.writeUTF("北京欢迎您");

        //保存一个对象
        oos.writeObject(new Dog("apple", 3));

        oos.close();
        System.out.println("数据保存完毕");
    }
}
package com.IO.inputstream;

import com.IO.outputStream.Dog;

import java.io.FileInputStream;
import java.io.ObjectInputStream;

public class ObjectInputStream_ {
    public static void main(String[] args) throws Exception {

        //选中要反序列化的文件
        String filePath = "D:\\news05.txt";

        ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filePath));

        //读取文件
        //读取(反序列化)要和保存数据(序列化)的顺序一致

        System.out.println(ois.readInt());
        System.out.println(ois.readBoolean());
        System.out.println(ois.readChar());
        System.out.println(ois.readDouble());
        System.out.println(ois.readUTF());

        //dog的编译类型是 Object , dog的运行类型是 Dog
        Object dog = ois.readObject();
        System.out.println("dog的运行类型:" + dog.getClass());
        System.out.println("dog的信息:"+dog);

        //如果需要调用Dog类的方法,需要先向下转型
        Dog dog2 = (Dog) dog;
        System.out.println(dog2.getName());

        ois.close();
    }
}

image


标准输入输出流

package com.IO.standard;

public class InputAndOutput {
    public static void main(String[] args) {

        //System 类的 public final static InputStream in = null;
        //System.in 编译类型 InputStream
        //System.in 运行类型 BufferedInputStream
        //表示的是标准输入 键盘
        System.out.println(System.in.getClass());//class java.io.BufferedInputStream


        //System.out public final static PrintStream out = null;
        //编译类型 PrintStream
        //运行类型 PrintStream
        //表示的是标准输出 显示器
        System.out.println(System.out.getClass());//class java.io.PrintStream
    }
}

转换流

image

image

直接读取可能会出现问题的代码:

package com.IO.transformation;

import java.io.BufferedReader;
import java.io.FileReader;

public class CodeQuestion {
    public static void main(String[] args) throws Exception {
        //读取D:\\news01.txt文件到程序

        //创建字符输入流 BufferedReader[]
        //使用 BufferedReader 对象读取 news01.txt
        //默认情况下,读取文件是按照 UTF-8 编码

        String filePath = "D:\\\\news01.txt";

        BufferedReader buf = new BufferedReader(new FileReader(filePath));

        System.out.println(buf.readLine());

        buf.close();

        //InputStreamReader
        //OutputStreamWriter

    }
}

操作文件属性:
image

输出结果:
image

可见出现了乱码,使用转换流处理:

InputStreamReader

package com.IO.transformation;


import java.io.*;

//InputStreamReader 转换流解决中文乱码问题
public class InputStreamReader_ {
    public static void main(String[] args) throws Exception {
        String filePath = "D:\\news01.txt";

        //1、new FileInputStream 转成 new InputStreamReader
        //2、指定编码 gbk
        InputStreamReader isr = new InputStreamReader(new FileInputStream(filePath), "gbk");

        //3、把 InputStreamReader 传入 BufferedReader
        BufferedReader br = new BufferedReader(isr);

        //4、读取

        String s = br.readLine();
        System.out.println(s);

        br.close();
        
    }
}

输出结果:
image

OutputStreamWriter

package com.IO.transformation;

import java.io.*;

public class OutputStreamWriter_ {
    public static void main(String[] args) throws Exception {
        String filePath = "D:\\news02.txt";
        String charSet = "utf-8";

        OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream(filePath), charSet);

        osw.write("你好,北京");

        osw.close();

        System.out.println("按照 " + charSet + " 方式保存成功");

    }
}

PrintStream

package com.IO.printStream;

import java.io.IOException;
import java.io.PrintStream;

public class PrintStream_ {
    public static void main(String[] args) throws IOException {

        PrintStream out = System.out;
        //在默认情况下,PrintStream 输出数据的位置是标准输出,即显示器
        out.print("Hello the world!");
        //print 也是使用的 write 方法来输出的,所以我们也可以直接使用 write 方法来输出
        out.write("Hello the world!".getBytes());

        out.close();

        //修改打印流输出的位置/设备
        System.setOut(new PrintStream("D:\\news02.txt"));
        System.out.println("修改打印流输出---测试");
    }
}

PrintWriter

package com.IO.transformation;

import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

public class printWriter_ {
    public static void main(String[] args) throws IOException {

        //PrintWriter printWriter = new PrintWriter(System.out);
        PrintWriter printWriter = new PrintWriter(new FileWriter("D:\\news01.txt"));

        printWriter.print("你好,北京");

        printWriter.close();//flush + 关闭流,才会将数据写入到文件
    }
}

Properties

package com.IO.properties;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Properties_ {
    public static void main(String[] args) throws IOException {

        //读取 mysql.properties 文件,得到 ip,user,pwd

        BufferedReader br = new BufferedReader(new FileReader("D:\\Projects\\JavaSE\\javase\\src\\mysql.properties"));

        String line = "";

        while ((line = br.readLine()) != null) {
            String[] split = line.split("=");
            System.out.println(split[0] + " 值是:" + split[1]);
        }
    }
}
package com.IO.properties;

import java.io.FileReader;
import java.io.IOException;
import java.util.Properties;

public class Properties02 {
    public static void main(String[] args) throws IOException {
        //使用 Properties 类来读取 mysql.properties 文件

        //1、创建 Properties 对象
        Properties properties = new Properties();

        //2、加载指定的配置文件
        properties.load(new FileReader("D:\\Projects\\JavaSE\\javase\\src\\mysql.properties"));

        //3、将 k-v显示到控制台
        properties.list(System.out);

        //4、根据 key 获取 value

        String user = properties.getProperty("user");
        String pwd = properties.getProperty("pwd");

        System.out.println("用户名:" + user);
        System.out.println("密码:" + pwd);

    }
}
package com.IO.properties;

import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Properties;

public class Propertied03 {
    public static void main(String[] args) throws IOException {

        //使用properties 来创建配置文件,修改配置文件内容

        Properties properties = new Properties();

        //创建
        //如果 key 不存在,这是创建;如果已经存在 key 就是修改
        properties.setProperty("charset", "utf8");
        properties.setProperty("user", "阿拉善");
        properties.setProperty("pwd", "654321");

        //将 k-v 存储到文件中
        properties.store(new FileOutputStream("D:\\Projects\\JavaSE\\javase\\src\\mysql2.properties"), null);
        System.out.println("保存配置文件成功~");


    }
}

标签:String,System,IO,import,new,public,out
来源: https://www.cnblogs.com/xiaojian1995/p/16548527.html

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