Class DriverManager

  1 /**Managing a collection of JDBC driven basic services  2 Note: The implementation of the new DataSource interface in the new JDBC 2.0 API provides another way to link data sources.  3 The object of using DataSource is the preferred solution.  4 */
  5 public class DriverManager {
  6 
  7     // Register the JDBC driver collection.
  8     private final static CopyOnWriteArrayList<DriverInfo> registeredDrivers = new CopyOnWriteArrayList<>();
  9   
 10     /**
 11     Initialize JDBC driver by checking jdcb.properties loading 12      */
 13     static {
 14         loadInitialDrivers();
 15         println("JDBC DriverManager initialized");
 16     }
 17 
 18 /*
 19 *The method of providing database connection for external use. 20 *The Reflection.getCallerClass () method is highlighted, which returns the class of the caller. 21 */
 22     @CallerSensitive
 23     public static Connection getConnection(String url)
 24         throws SQLException {
 25 
 26         java.util.Properties info = new java.util.Properties();
 27         return (getConnection(url, info, Reflection.getCallerClass()));
 28     }
 29 
 30     //  Create database links based on urls, corresponding attribute information, and finding the appropriate registered driver in registered Drivers
 31     private static Connection getConnection(
 32         String url, java.util.Properties info, Class<?> caller) throws SQLException {
 33         /*
 34          * When callerCl is null, we should check the application's
 35          * (which is invoking this class indirectly)
 36          * classloader, so that the JDBC driver class outside rt.jar
 37          * can be loaded from here.
 38          */
 39         ClassLoader callerCL = caller != null ? caller.getClassLoader() : null;
 40         synchronized(DriverManager.class) {
 41             // synchronize loading of the correct classloader.
 42             if (callerCL == null) {
 43                 callerCL = Thread.currentThread().getContextClassLoader();
 44             }
 45         }
 46 
 47         if(url == null) {
 48             throw new SQLException("The url cannot be null", "08001");
 49         }
 50 
 51         println("DriverManager.getConnection(\"" + url + "\")");
 52 
 53         // Walk through the loaded registeredDrivers attempting to make a connection.
 54         // Remember the first exception that gets raised so we can reraise it.
 55         SQLException reason = null;
 56 
 57         for(DriverInfo aDriver : registeredDrivers) {
 58             // If the caller does not have permission to load the driver then
 59             // skip it.
 60          //There may be multiple database drivers in an application that need to determine whether the caller of the database connection (the object that calls the getConnection () method) matches the driver
 61             if(isDriverAllowed(aDriver.driver, callerCL)) {
 62                 try {
 63                     println("    trying " + aDriver.driver.getClass().getName());
 64                     Connection con = aDriver.driver.connect(url, info);
 65                     if (con != null) {
 66                         // Success!
 67                         println("getConnection returning " + aDriver.driver.getClass().getName());
 68                         return (con);
 69                     }
 70                 } catch (SQLException ex) {
 71                     if (reason == null) {
 72                         reason = ex;
 73                     }
 74                 }
 75 
 76             } else {
 77                 println("    skipping: " + aDriver.getClass().getName());
 78             }
 79 
 80         }
 81 
 82         // if we got here nobody could connect.
 83         if (reason != null)    {
 84             println("getConnection failed: " + reason);
 85             throw reason;
 86         }
 87 
 88         println("getConnection: no suitable driver found for "+ url);
 89         throw new SQLException("No suitable driver found for "+ url, "08001");
 90     }
 91 }
 92 
 93 //There may be multiple database drivers in an application that need to determine whether the caller of the database connection (the object that calls the getConnection () method) matches the driver
 94 private static boolean isDriverAllowed(Driver driver, ClassLoader classLoader) {
 95         boolean result = false;
 96         if(driver != null) {
 97             Class<?> aClass = null;
 98             try {
 99                 aClass =  Class.forName(driver.getClass().getName(), true, classLoader);
100             } catch (Exception ex) {
101                 result = false;
102             }
103 
104              result = ( aClass == driver.getClass() ) ? true : false;
105         }
106 
107         return result;
108     }
109 
110 //Get the driver from registeredDrivers based on the URL, and match in registeredDrivers based on the caller class returned by Reflection. getCallerClass ()
111   @CallerSensitive
112     public static Driver getDriver(String url)
113         throws SQLException {
114 
115         println("DriverManager.getDriver(\"" + url + "\")");
116 
117         Class<?> callerClass = Reflection.getCallerClass();
118 
119         // Walk through the loaded registeredDrivers attempting to locate someone
120         // who understands the given URL.
121         for (DriverInfo aDriver : registeredDrivers) {
122             // If the caller does not have permission to load the driver then
123             // skip it.
124             if(isDriverAllowed(aDriver.driver, callerClass)) {
125                 try {
126                     if(aDriver.driver.acceptsURL(url)) {
127                         // Success!
128                         println("getDriver returning " + aDriver.driver.getClass().getName());
129                     return (aDriver.driver);
130                     }
131 
132                 } catch(SQLException sqe) {
133                     // Drop through and try the next driver.
134                 }
135             } else {
136                 println("    skipping: " + aDriver.driver.getClass().getName());
137             }
138 
139         }
140 
141         println("getDriver: no suitable driver");
142         throw new SQLException("No suitable driver", "08001");
143     }
144 
145 
146 /*
147 *Registration data-driven, using synchronous mode, and finally saved in CopyOnWriteArrayList collection.148 */
149     public static synchronized void registerDriver(java.sql.Driver driver,
150             DriverAction da)
151         throws SQLException {
152 
153         /* Register the driver if it has not already been added to our list */
154         if(driver != null) {
155             registeredDrivers.addIfAbsent(new DriverInfo(driver, da));
156         } else {
157             // This is for compatibility with the original DriverManager
158             throw new NullPointerException();
159         }
160 
161         println("registerDriver: " + driver);
162 
163     }