Talking about Properties Collection

1 Overview

java.util.PropertiesInherited from Hashtableto represent a persistent property set. It stores data using a key-value structure, where each key and its corresponding value is a string. This class is also used by many Java classes. For example, when obtaining system properties, System.getPropertiesthe method returns an Propertiesobject.

2 Properties class

Construction method

public Properties(): Creates an empty property list.

unique method

method name	illustrate
Object setProperty(String key, String value)	Set the key and value of the collection, both of which are of String type, and call the Hashtable method put at the bottom.
String getProperty(String key)	Searches for properties using the keys specified in this property list.
Set<String> stringPropertyNames()	Returns an unmodifiable set of keys from this property list, where the keys and their corresponding values are strings.

Methods related to streams

method name	illustrate
void load(InputStream inStream)	Reads a property list (key and element pair) from the input byte stream
void load(Reader reader)	Reads a property list (key and element pair) from an input character stream
void store(OutputStream out, String comments)	Writes this list of properties (key and element pairs) into this Properties table, in a format suitable for use with the load(InputStream) method to an output byte stream.
void store(Writer writer, String comments)	Writes this list of properties (key and element pairs) into this Properties table, in a format suitable for use with the load(Reader) method to an output character stream.

public void load(InputStream inStream): Read key-value pairs from a byte input stream.
public void load(Reader reader): Read key-value pairs from a character input stream.

The byte input stream is used in the parameter. Through the stream object, it can be associated with a file, so that the data in the text can be loaded. Text data format:

filename=a.txt
length=209385038
location=D:\a.txt

Load code demo:

public static void main(String[] args) throws FileNotFoundException {
    // 创建属性集对象
    Properties pro = new Properties();
    // 加载文本中信息到属性集
    pro.load(new FileInputStream("read.txt"));
    // 遍历集合并打印
    Set<String> strings = pro.stringPropertyNames();
    for (String key : strings ) {
    	System.out.println(key+" -- "+pro.getProperty(key));
    }
}

public void store(OutputStream outStream,String comments): save the key-value pairs of the Properties collection object to the file
public void store(Writer writer,String comments): Save the key-value pairs of the Properties collection object to the file

public static void main(String[] args) throws IOException {
        // 创建Properties集合对象
        Properties props = new Properties();

        // 创建InputStream/Reader的子类对象,绑定源文件
        InputStream is = new FileInputStream("day13_sw\\src\\config.properties");

        // Properties集合对象调用load方法传递InputStream/Reader的子类对象,
        // 把文件内容以键值对的方式加载到Properties集合对象中
        props.load(is);

        // 遍历集合
        Set<String> propertyNames = props.stringPropertyNames();

        for (String propertyName : propertyNames) {
            String propertyValue = props.getProperty(propertyName);
            if("age".equals(propertyName)) {//age属性的值增加10岁
                props.setProperty(propertyName,Integer.parseInt(propertyValue)+10+"");
            }
        }
        OutputStream os = new FileOutputStream("day13_sw\\src\\config.properties");
        // 把Properties集合对象中的内容存储到文件中
        props.store(os,null);
    }