Class.forName("com.mysql.jdbc.Driver");
public class Driver extends NonRegisteringDriver implements java.sql.Driver {
static {
try {
java.sql.DriverManager.registerDriver(new Driver()); //先执行DriverManager的初始化，再registerDriver方法，静态代码只走一次。
}
}
DriverManager类初始化：
static {
loadInitialDrivers(); //静态代码只走一次
}
private static void loadInitialDrivers() {
String drivers;
try {
drivers = AccessController.doPrivileged(new PrivilegedAction() {
public String run() {
return System.getProperty("jdbc.drivers"); //null
}
});
}
AccessController.doPrivileged(new PrivilegedAction() {
public Void run() {
ServiceLoader loadedDrivers = ServiceLoader.load(Driver.class); //loadedDrivers = java.sql.Driver接口
Iterator driversIterator = loadedDrivers.iterator();
try{
while(driversIterator.hasNext()) { //加载META-INF/services/java.sql.Driver，找到mysql-connector-java-5.1.45.jar!/META-INF/services/java.sql.Driver返回[com.mysql.jdbc.Driver, com.mysql.fabric.jdbc.FabricMySQLDriver]
driversIterator.next();
//class com.mysql.jdbc.Driver反射出对象时候不会去执行java.sql.DriverManager.registerDriver(new Driver());因为上面已经走了一次，com.mysql.jdbc.Driver此时不在DriverManager的registeredDrivers里面，
com.mysql.jdbc.Driver是在DriverManager静态代码执行完之后通过registerDriver方法加到registeredDrivers里面去的。
//com.mysql.fabric.jdbc.FabricMySQLDriver反射时候去执行java.sql.DriverManager.registerDriver(new Driver());把自己加到DriverManager的registeredDrivers里面。但是DriverManager的静态代码不会执行。因为执行过一次。
}
}
return null;
}
});
}
public class FabricMySQLDriver extends NonRegisteringDriver implements Driver {
static {
try {
DriverManager.registerDriver(new FabricMySQLDriver()); //静态代码只走一次。
}
}
}
Original: https://www.cnblogs.com/yaowen/p/12273232.html
Author: 哈哈呵h
Title: JDBC事务2
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