Steps of the JDBC Connection database query information (extracted as configuration file mode)

The drawbacks of hard-coded formats: When a database changes, you re-modify the code, recompile, and deploy

Workaround: Write the database information in the configuration file and let the program read the configuration file to obtain this information

jdbc.driver.class=com.mysql.jdbc.driverjdbc.connection.url=jdbc:mysql://127.0.0.1:3306/ treejdbc.connection.username=rootjdbc.connection.password=123321

Writing a configuration file database.properties
Create Package Com.pb.tree.util, write class ConfigManager read properties file

Package cn.tree.util;

Import java.io.IOException;
Import Java.io.InputStream;
Import java.util.Properties;

Tool classes for reading configuration files-Singleton mode
public class ConfigManager {
Read configuration file Properties.load (InputStream)

private static ConfigManager ConfigManager;
private static properties properties;

Private ConfigManager () {
String configfile = "Database.properties";
Properties = new properties ();
InputStream is = ConfigManager.class.getClassLoader ()
. getResourceAsStream (ConfigFile);

try {
Properties.load (IS);
Is.close ();
} catch (IOException e) {
E.printstacktrace ();
}
}

public static ConfigManager getinstance () {
if (ConfigManager = = null) {
ConfigManager = new ConfigManager ();
}
return ConfigManager;
}

public string getString (string key) {
return Properties.getproperty (key);
}

}

Ways to modify query information for the Menudao class

Package Cn.tree.util;import Java.io.ioexception;import Java.io.inputstream;import java.util.properties;// Tool class for reading configuration files-Singleton mode public class ConfigManager {//Read config file properties.load (inputstream) private static ConfigManager Configmanager;private static Properties properties;private ConfigManager () {String configfile = "Database.properties"; Properties = new properties (); InputStream is = ConfigManager.class.getClassLoader (). getResourceAsStream (ConfigFile); try {properties.load (IS); Is.close ();} catch (IOException e) {e.printstacktrace ()}} public static ConfigManager getinstance () {if (ConfigManager = = null) {ConfigManager = new ConfigManager ();} return ConfigManager;} public string getString (string key) {return Properties.getproperty (key);}}

　　

Package Cn.tree.dao;import Java.sql.connection;import Java.sql.drivermanager;import java.sql.resultset;import Java.sql.sqlexception;import Java.sql.statement;import Cn.tree.util.configmanager;public class MenuDao {// Query home directory public void Getmainlist () {Connection Connection = null; Statement st = null; ResultSet rs = null; String Driver = Configmanager.getinstance (). getString ("Jdbc.driver.class"); String URL = configmanager.getinstance (). getString ("Jdbc.connection.url"); String username = configmanager.getinstance (). getString ("Jdbc.connection.username"); String password = configmanager.getinstance (). getString ("Jdbc.connection.password"); try {//1, Load drive class.forname ( driver);//2, get database connection connection = drivermanager.getconnection (URL, username, password);//3, Get Statement object, Execute SQL statement String sql = "SELECT * from main"; st = Connection.createstatement (); rs = st.executequery (sql);//4, processing SQL execution result while ( Rs.next ()) {int id = rs.getint ("id"); String name = rs.getstring ("name"); SYSTEM.OUT.PRINTLN ("ID:" + id + "\ T")+ "Name:" + name);}} catch (ClassNotFoundException e) {e.printstacktrace ()} catch (SQLException e) {e.printstacktrace ();} finally {try {//5, Release resources Rs.close (); St.close (); Connection.close ();} catch (SQLException e) {e.printstacktrace ();}}} public static void Main (string[] args) {Menudao Menudao = new Menudao (); Menudao.getmainlist ();}}

　　

Steps of the JDBC Connection database query information (extracted as configuration file mode)