Understanding and learning of properties class and properties configuration file

introduction

Maybe our java While the program is running , We need to modify one of the configured values , But it is impossible for us to modify the value after stopping the program , This is the time , It reflects the use properties The benefits of configuration files .

If the value is properties In the configuration file , It can follow very well and conveniently java Programs interact , We don't need to stop the program , Can be modified directly properties Values in the configuration file , that java This value in the program can be changed .

and Properties class , yes java Read from the program properties Preferred class of configuration file , So we need to master it ！

Basic introduction

The parent class of this class is HashTable, So is the underlying principle HashTable

This class is specially used for reading and writing properties Collection class of configuration file , The configuration file format is as follows ：

 key = value 
 key = value 

** Be careful ：** Key value pairs do not need spaces , Values do not need to be enclosed in quotation marks , The default type is String

Common methods

• load： Load the key value pair of the configuration file to Properties object
• list： Display data to the specified device
• getProperty(key)： Get value from key
• setProperty(key,value)： Set key value pair to Properties object
• store： take Properties The key value pairs in are stored in the configuration file , stay idea Save information to the configuration file , If it contains Chinese , Will be stored as unicode code

Requirements coding

demand 1： Read profile content

The following configuration file mysql.properties

ip=0.0.0.0
user=root
pwd=root

stay java Read its value in the program

The traditional way to achieve

Use character stream to read

/** * @author: Lei Zijie  * @date:2022/7/27 */
public class Properties01 {
    
    public static void main(String[] args) throws IOException {
    
        // Get the current working directory , Back file The relative path of is written according to this 
        //System.out.println(System.getProperty("user.dir"));//E:\Allworkspaces\idea-workspace\JavaEE
        
        File file = new File("basic_review\\src\\properties_\\mysql.properties");
        BufferedReader bufferedReader = new BufferedReader(new FileReader(file));
        String line;
        while((line = bufferedReader.readLine())!=null){
    
            // Split the read string 
            String[] split = line.split("=");
            System.out.println(split[0]+" The value is ："+split[1]);

            // The following is the output of all the contents 
            //System.out.println(line);
        }
        bufferedReader.close();
    }
}

Use Properties Class read

Use Properties Class to read the contents of the configuration file

/** * *  Use Properties To read the file  * * @author: Lei Zijie  * @date:2022/7/27 */
public class Properties02 {
    
    public static void main(String[] args) throws IOException {
    

        Properties properties = new Properties();
        // Get the current working directory , Back file The relative path of is written according to this 
        //System.out.println(System.getProperty("user.dir"));//E:\Allworkspaces\idea-workspace\JavaEE
        // Loads the specified configuration file , The relative path is the relative path of the current working directory 
        properties.load(new FileReader("basic_review\\src\\properties_\\mysql.properties"));
        // take k-v Display console 
        properties.list(System.out);

        System.out.println("=====================");
        // according to key Get the value for 
        String user = properties.getProperty("user");
        String pwd = properties.getProperty("pwd");
        System.out.println(" user name ："+user);
        System.out.println(" password ："+pwd);

    }
}

demand 2： Add profile content

take Properties The key value pairs created by the class are written to a new file

/** * *  Use properties Class to create a configuration file  * * @author: Lei Zijie  * @date:2022/7/27 */
public class Properties03 {
    
    public static void main(String[] args) throws IOException {
    

        Properties properties = new Properties();

        // establish 
        properties.setProperty("user","lzj");// If the user name is Chinese , Will save unicode code 
        properties.setProperty("pwd","123456");
        properties.setProperty("age","22");

        // Store in file 
        // In formal parameter comments by null that will do , If you add, you are adding comments 
        properties.store(new FileOutputStream("basic_review\\src\\properties_\\mysql2.properties"),null);
        System.out.println(" Successfully saved the configuration ");

    }
}

demand 3： Modify the read configuration file

Read first , Then modify the configuration and write it to the original file

/** * *  Use Properties To modify the read file  * * @author: Lei Zijie  * @date:2022/7/27 */
public class Properties04 {
    
    public static void main(String[] args) throws IOException {
    

        Properties properties = new Properties();
        // Get the current working directory , Back file The relative path of is written according to this 
        //System.out.println(System.getProperty("user.dir"));//E:\Allworkspaces\idea-workspace\JavaEE
        // Loads the specified configuration file , The relative path is the relative path of the current working directory 
        properties.load(new FileReader("basic_review\\src\\properties_\\mysql.properties"));
        // take k-v Display console 
        properties.list(System.out);

        // modify user
        properties.setProperty("user","lzj");

        System.out.println("=====================");
        // according to key Get the value for 
        String user = properties.getProperty("user");
        String pwd = properties.getProperty("pwd");
        System.out.println(" user name ："+user);
        System.out.println(" password ："+pwd);

        // Write the modified key value pair into the file 
        properties.store(new FileOutputStream("basic_review\\src\\properties_\\mysql.properties"),null);

    }
}

All the way

Modifier and Type	Method and Description
String	getProperty(String key) Use the key specified in this property list to search for properties .
String	getProperty(String key, String defaultValue) Use the key specified in this property list to search for properties .
void	list(PrintStream out) Print this property list to the specified output stream .
void	list(PrintWriter out) Print this property list to the specified output stream .
void	load(InputStream inStream) Read the attribute list from the input byte stream （ Bond and element pair ）.
void	load(Reader reader) Read the attribute list from the input character stream in a simple linear format （ Keywords and element pairs ）.
void	loadFromXML(InputStream in) The... In the input stream will be specified XML All properties represented by the document are loaded into this property sheet .
Enumeration<?>	propertyNames() Returns an enumeration of all keys in this property list , Include different keys in the default attribute list , If a key with the same name has not been found in the main attribute list .
void	save(OutputStream out, String comments) Have been abandoned If... Occurs while saving the attribute list I / O error , This method will not throw IOException. Save the property list store(OutputStream out, String comments) The way is through store(OutputStream out, String comments) Method or storeToXML(OutputStream os, String comment) Method .
Object	setProperty(String key, String value) Call Hashtable Method put .
void	store(OutputStream out, String comments) Add this property to the list （ Bond and element pair ） Write this Properties In the table , To be suitable for use load(InputStream) Method is loaded to Properties Format output stream in table .
void	store(Writer writer, String comments) Add this property to the list （ Bond and element pair ） Write this Properties In the table , To be fit for use load(Reader) Method to the output character stream .
void	storeToXML(OutputStream os, String comment) Issue a that represents all the attributes contained in this table XML file .
void	storeToXML(OutputStream os, String comment, String encoding) Issue a that represents all attributes contained in this table using the specified encoding XML file .
Set<String>	stringPropertyNames() Returns a set of keys in this property list , Where the key and its corresponding value are strings , Include different keys in the default attribute list , If a key with the same name has not been found in the main attribute list .