与IO流相结合的集合——Properties

Properties

表示可以从流中读取，也可以加载到流中
继承了Hashtable

1. 遍历

package com.itheima.demo07.Prop;

import java.util.Properties;
import java.util.Set;

public class Demo01Properties {
    
    
    public static void main(String[] args) {
    
    
        Properties properties = new Properties();
        properties.setProperty("filename", "a.txt");
        properties.setProperty("length", "209385038");
        properties.setProperty("location", "D:\\a.txt");
        System.out.println(properties);
        /*遍历打印属性集*/
        Set<String> strings = properties.stringPropertyNames();
        for (String s : strings) {
    
    
            System.out.println(properties.getProperty(s));
        }
    }
}

运行结果

{location=D:\a.txt, filename=a.txt, length=209385038}
D:\a.txt
a.txt
209385038

2. 集合->硬盘 store

对应字符流中的FileWriter，将数据从内存中写出
对应字节流中的FileOutputStream，将数据从内存中输出

public void store(Writer writer, String comments)
        throws IOException
        {
    
    
            store0((writer instanceof BufferedWriter)?(BufferedWriter)writer
                            : new BufferedWriter(writer),
                    comments,
                    false);
        }
public void store(OutputStream out, String comments)
        throws IOException
    {
    
    
        store0(new BufferedWriter(new OutputStreamWriter(out, "8859_1")),
               comments,
               true);
    }

第一种：字符输出流，可以写中文
第二种：字节输出流，不能写中文

2.1 字符流FileWriter写文件

//使用字符流
package com.itheima.demo07.Prop;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.Properties;

public class Demo02Properties {
    
    
    public static void main(String[] args) throws IOException {
    
    
        Properties properties = new Properties();
        properties.setProperty("filename", "a.txt");
        properties.setProperty("length", "209385038");
        properties.setProperty("location", "D:\\a.txt");
        //创建一个字符流
        FileWriter fw = new FileWriter("h.txt");
        properties.store(fw, "sava date");
        fw.close();
    }
}

运行结果

2.2 字节流FileOutputStream从内存中输出

//使用字节流
package com.itheima.demo07.Prop;

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

public class Demo03Properties {
    
    
    public static void main(String[] args) throws IOException {
    
    
        Properties properties = new Properties();
        properties.setProperty("filename", "a.txt");
        properties.setProperty("length", "209385038");
        properties.setProperty("location", "D:\\a.txt");
        //创建一个字节流
        FileOutputStream fos = new FileOutputStream("h.txt");
        properties.store(fos, "sava date");
        fos.close();
    }
}

运行结果

3. 硬盘->集合 load

对应字符流中的FileRead，将数据从内存中读出
对应字节流中的FileInputStream，将数据从内存中输入

public synchronized void load(Reader reader) throws IOException {
    
    
        load0(new LineReader(reader));
    }
public synchronized void load(InputStream inStream) throws IOException {
    
    
        load0(new LineReader(inStream));
    }

第一种：字符输入流，可以写中文
第二种：字节输入流，不能写中文

3.1 字符流FileRead读文件

package com.itheima.demo07.Prop;

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

public class Demo04Properties {
    
    
    public static void main(String[] args) throws IOException {
    
    
        Properties properties = new Properties();
        FileReader fr = new FileReader("h.txt");
        System.out.println(properties);
        properties.load(fr);
        System.out.println(properties);
        Set<String> strings = properties.stringPropertyNames();
        for (String s : strings) {
    
    
            System.out.println(properties.getProperty(s));
        }
    }
}

运行结果

{}
{location=D:\a.txt, filename=a.txt, length=209385038}
D:\a.txt
a.txt
209385038

3.2 字节流FileInputStream输入到内存

package com.itheima.demo07.Prop;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;
import java.util.Set;

public class Demo05Properties {
    
    
    public static void main(String[] args) throws IOException {
    
    
        Properties properties = new Properties();
        FileInputStream fis = new FileInputStream("h.txt");
        System.out.println(properties);
        properties.load(fis);
        System.out.println(properties);
        Set<String> strings = properties.stringPropertyNames();
        for (String s : strings) {
    
    
            System.out.println(properties.getProperty(s));
        }
    }
}

运行结果

{}
{location=D:\a.txt, filename=a.txt, length=209385038}
D:\a.txt
a.txt
209385038

tip:在文件中被连接的键值对，可以用等号，空格相连
在文件中，可以是用#进行注释
默认的键值对的读取都是字符串，不需要加""