Java Foundation - Properties Collection of IO Stream Objects
Author: Yin Zhengjie
Copyright statement: original works, please do not reprint! Otherwise held liable.
1. Characteristics of the Properties collection
The Properties class represents a persistent set of properties. Properties can be stored in or loaded from a stream, and each key in the property list and its corresponding value is a string. Summarizing its obvious features are as follows:
1>. A subclass of Hashtable, the methods in the map collection are available;
2>. The set has no generic type, and the keys and values are all strings;
3>. It is a persistent attribute set, and the key value can be stored in the set or in persistent devices (hard disk, U disk, CD-ROM). The source of the key value can also be a persistent device.
4>. There are methods combined with flow count such as: " ", " ", " ", " ".load(InputStream inStream)load(Reader reader)store(OutputStream out, String comments)store(Writer writer, String comments)
2. Common methods of Properties collection
1>.Properties collection stores key-value pairs
1 /* 2 @author :yinzhengjie 3 Blog:http://www.cnblogs.com/yinzhengjie/tag/Java%E5%9F%BA%E7%A1%80/ 4 EMAIL:[email protected] 5 */ 6 7 package cn.org.yinzhengjie.note6; 8 9 import java.util.Properties; 10 import java.util.Set; 11 12 public class PropertiesDemo { 13 public static void main(String[] args) { 14 Properties p = new Properties(); 15 //1>. Use the setProperty method to store key-value pairs. The bottom layer calls the put method of the parent class (Hashtable), which can be viewed through the source code. 16 p.setProperty("Name", "yinzhengjie" ); 17 p.setProperty("Age", "18" ); 18 p.setProperty("Hobby", "Cosplay" ); 19 20 System.out.println( p); 21 // 2>. Get the value by key, and return null if the given key value does not exist. 22 String value = p.getProperty("Name1" ); 23 System.out.println(value); 24 25 // 3>. Traverse the Properties collection through the stringPropertyNames method, which stores the keys in the collection to the Set collection, Similar to the method keySet of the Map interface. 26 Set<String>27 for (String key : set) { 28 System.out.println(key+"==="+ p.getProperty(key)); 29 } 30 31 } 32 } 33 34 35 /* 36 The execution result of the above code is as follows: 37 {Hobby=Cosplay, Age=18, Name=yinzhengjie} 38 null 39 Hobby===Cosplay 40 Age===18 41 Name===yinzhengjie 42 */
2>.(load method) The stream object reads the key-value pair in the file and saves it to the collection
1 /* 2 @author :yinzhengjie 3 Blog:http://www.cnblogs.com/yinzhengjie/tag/Java%E5%9F%BA%E7%A1%80/ 4 EMAIL:[email protected] 5 */ 6 7 package cn.org.yinzhengjie.note6; 8 9 import java.io.FileReader; 10 import java.io.IOException; 11 import java.util.Properties; 12 13 public class PropertiesDemo { 14 public static void main(String[] args) throws IOException { 15 Properties p = new Properties(); 16 // Create a character stream object to read the file 17 FileReader fr = new FileReader("yinzhengjie.properties" ); 18 // Call the method load of the collection, pass the character input stream, put The contents of the file are loaded into the p object. 19 p.load(fr); 20 // After loading, the fr stream object has no use value, just turn it off. 21 fr.close(); 22 System.out.println(p); 23 24 } 25 } 26 27 /* 28 The execution result of the above code is as follows: 29 {name=yinzhengjie, age=18, [email protected] } 30 */
3>. (store method) Write the key-value pairs in the collection to a file and save
1 /* 2 @author :yinzhengjie 3 Blog:http://www.cnblogs.com/yinzhengjie/tag/Java%E5%9F%BA%E7%A1%80/ 4 EMAIL:[email protected] 5 */ 6 7 package cn.org.yinzhengjie.note6; 8 9 import java.io.FileWriter; 10 import java.io.IOException; 11 import java.util.Properties; 12 import java.util.Set; 13 14 public class PropertiesDemo { 15 public static void main(String[] args) throws IOException { 16 Properties p = new Properties(); 17 // 1>. Use the setProperty method to store key-value pairs, and the bottom layer calls the put method of the parent class (Hashtable), which can be viewed through the source code. 18 p.setProperty("Name", "yinzhengjie" ); 19 p.setProperty("Age", "18" ); 20 p.setProperty("Hobby", "Cosplay" ); 21 22 FileWriter fw = new FileWriter( "yinzhengjie.properties" ); 23 // Write the key-value pair to the file, and use the collection method store to pass the character output stream. 24 p.store(fw, "Add by yinzhengjie"); 25 26 } 27 }
After execution, a new file will be generated with the following content:
3. Small test knife
Limit the number of game trials, define a file with the content: "times=5", this parameter indicates the number of times the player can experience the game, when the value is 0, the utility ends.
1 #Sat May 05 17:38:45 GMT+08:00 2018 2 times=5
1 /* 2 @author :yinzhengjie 3 Blog: http://www.cnblogs.com/yinzhengjie/tag/Java%E5%9F%BA%E7%A1%80/ 4 EMAIL:[email protected] 5 */ 6 7 package cn.org.yinzhengjie.note6; 8 9 import java.io.FileInputStream; 10 import java.io.FileOutputStream; 11 import java.util.Properties; 12 13 /* 14 * Properties do not belong to the io stream system, java Under the .util package. 15 * Use as a subclass of Hashtable 16 * 17 */ 18 public class PropertiesDemo { 19 20 public static void main(String[] args) throws Exception { 21 Properties p = new Properties(); 22 p.load(new FileInputStream("yinzhengjie.properties")); 23 24 String times = p.getProperty("times"); 25 int i = Integer.parseInt(times); 26 27 if(i <= 0){ 28 System.out.println("试用结束"); 29 }else{ 30 System.out.println("Currently: " + (5 - i + 1) + " times, remaining: " + (i - 1) + " times" ); 31 play(); 32 p .setProperty("times", i - 1 + "" ); 33 p.store( new FileOutputStream("yinzhengjie.properties"), null ); 34 } 35 } 36 37 private static void play() { 38 System.out .println("Playing game..." ); 39 } 40 41 }