brpublic class UserDAOImpl{ brbr public void save() { br // TODO Auto-generated method stub br System.out.println(user saved); br } br} br//相关配置,省略了一些不相关内容 brbean id=userDAO class=UserDAOImpl brbean id=userDAOProxy class=org.
public class UserDAOImpl{
public void save() {
// TODO Auto-generated method stub
System.out.println("user saved");
}
}
//相关配置,省略了一些不相关内容
测试代码
ApplicationContext ctx =new FileSystemXmlApplicationContext("applicationContext.xml");
UserDAOImpl userDAOImpl =
(UserDAOImpl)ctx.getBean("userDAOProxy");
userDAOImpl.save();
上面这种情况下程序可以正常运行,但是如果UserDAOImpl实现了一个接口,其他不变
public class UserDAOImpl implements UserDAO {public void save() {
// TODO Auto-generated method stub
System.out.println("user saved");
}
}
这种情况下,程序将不能正常运行,会抛出java.lang.ClassCastException异常
理解上面这种情况产生的原因需要了解Spring AOP的实现原理。
Spring 实现AOP是依赖JDK动态代理和CGLIB代理实现的。
以下是JDK动态代理和CGLIB代理简单介绍
JDK动态代理:其代理对象必须是某个接口的实现,它是通过在运行期间创建一个接口的实现类来完成对目标对象的代理。
CGLIB代理:实现原理类似于JDK动态代理,只是它在运行期间生成的代理对象是针对目标类扩展的子类。CGLIB是高效的代码生成包,底层是依靠ASM(开源的java字节码编辑类库)操作字节码实现的,性能比JDK强。
Spring是依靠什么来判断采用哪种代理策略来生成AOP代理呢?以下代码就是Spring的判断逻辑
advisedSupport.isOptimize()与advisedSupport.isProxyTargetClass()默认返回都是false,所以在默认情况下目标对象有没有实现接口决定着Spring采取的策略,当然可以设置advisedSupport.isOptimize()或者advisedSupport.isProxyTargetClass()返回为true,这样无论目标对象有没有实现接口Spring都会选择使用CGLIB代理。所以在默认情况下,如果一个目标对象如果实现了接口Spring则会选择JDK动态代理策略动态的创建一个接口实现类(动态代理类)来代理目标对象,可以通俗的理解这个动态代理类是目标对象的另外一个版本,所以这两者之间在强制转换的时候会抛出j ava.lang.ClassCastException。而所以在默认情况下,如果目标对象没有实现任何接口,Spring会选择CGLIB代理, 其生成的动态代理对象是目标类的子类。
以上说的是默认情况下,也可以手动配置一些选项使Spring采用CGLIB代理。
org.springframework.transaction.interceptor.TransactionProxyFactoryBean是org.springframework.aop.framework. ProxyConfig的子类,所以可以参照ProxyConfig里的一些设置如下所示,将optimize和proxyTargetClass任意一个设置为true都可以强制Spring采用CGLIB代理。
//相关配置,省略了一些不相关内容使用CGLIB代理也就不会出现前面提到的ClassCastException问题了,
也可以在性能上有所提高,但是也有它的弊端,Spring doc原文解释如下optimization will usually mean that advice changes won't take effect after a proxy has been created. For this reason, optimization is disabled by default。

InnoDBBufferPool reduces disk I/O by caching data and indexing pages, improving database performance. Its working principle includes: 1. Data reading: Read data from BufferPool; 2. Data writing: After modifying the data, write to BufferPool and refresh it to disk regularly; 3. Cache management: Use the LRU algorithm to manage cache pages; 4. Reading mechanism: Load adjacent data pages in advance. By sizing the BufferPool and using multiple instances, database performance can be optimized.

Compared with other programming languages, MySQL is mainly used to store and manage data, while other languages such as Python, Java, and C are used for logical processing and application development. MySQL is known for its high performance, scalability and cross-platform support, suitable for data management needs, while other languages have advantages in their respective fields such as data analytics, enterprise applications, and system programming.

MySQL is worth learning because it is a powerful open source database management system suitable for data storage, management and analysis. 1) MySQL is a relational database that uses SQL to operate data and is suitable for structured data management. 2) The SQL language is the key to interacting with MySQL and supports CRUD operations. 3) The working principle of MySQL includes client/server architecture, storage engine and query optimizer. 4) Basic usage includes creating databases and tables, and advanced usage involves joining tables using JOIN. 5) Common errors include syntax errors and permission issues, and debugging skills include checking syntax and using EXPLAIN commands. 6) Performance optimization involves the use of indexes, optimization of SQL statements and regular maintenance of databases.

MySQL is suitable for beginners to learn database skills. 1. Install MySQL server and client tools. 2. Understand basic SQL queries, such as SELECT. 3. Master data operations: create tables, insert, update, and delete data. 4. Learn advanced skills: subquery and window functions. 5. Debugging and optimization: Check syntax, use indexes, avoid SELECT*, and use LIMIT.

MySQL efficiently manages structured data through table structure and SQL query, and implements inter-table relationships through foreign keys. 1. Define the data format and type when creating a table. 2. Use foreign keys to establish relationships between tables. 3. Improve performance through indexing and query optimization. 4. Regularly backup and monitor databases to ensure data security and performance optimization.

MySQL is an open source relational database management system that is widely used in Web development. Its key features include: 1. Supports multiple storage engines, such as InnoDB and MyISAM, suitable for different scenarios; 2. Provides master-slave replication functions to facilitate load balancing and data backup; 3. Improve query efficiency through query optimization and index use.

SQL is used to interact with MySQL database to realize data addition, deletion, modification, inspection and database design. 1) SQL performs data operations through SELECT, INSERT, UPDATE, DELETE statements; 2) Use CREATE, ALTER, DROP statements for database design and management; 3) Complex queries and data analysis are implemented through SQL to improve business decision-making efficiency.

The basic operations of MySQL include creating databases, tables, and using SQL to perform CRUD operations on data. 1. Create a database: CREATEDATABASEmy_first_db; 2. Create a table: CREATETABLEbooks(idINTAUTO_INCREMENTPRIMARYKEY, titleVARCHAR(100)NOTNULL, authorVARCHAR(100)NOTNULL, published_yearINT); 3. Insert data: INSERTINTObooks(title, author, published_year)VA


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