J2EE学习笔记之数据库操作
学习目标:
学会安装数据库(MySQL)、加载JDBC驱动程序
掌握如何在JSP中连接MySQL,并执行诸如创建数据库表、添加、更新、删除记录等操作
(一)下载并安装MySQL
具体操作略,可以百度一下
(二)下载并安装MySQL
访问MySQL官网,找到下载链接下载mysql-connector-java-XXXX.zip
安装MySQL的方法为:将下载的mysql-conntector-java-XXX.zip解压后的mysql-conntector-java-XXX.jar拷贝到Web项目的WEB-INF目录的lib目录下。
(三)加载JDBC驱动程序
JDBC与数据库建立连接前必须加载适当的驱动程序。方法:使用Class的forName方法来加载驱动程序。
示例如下:
try{
Class.forName("com.mysql.jdbc.Driver");//加载JDBC驱动程序
}catch(ClassNotFoundException e){
out.println("加载驱动失败");
}
%>
(四)数据库操作
示例说明:
String url="数据库实例的URL";
String user="root";//用户名
String passwd="XXX";//连接密码
Connection conn=null;
try{
Class.forName("com.mysql.jdbc.Driver");//加载JDBC驱动程序
conn=DriverManager.getConnection(url,user,passwd);
}catch(ClassNotFoundException e){
out.println("找不到驱动类");
}catch(SQLException e){
out.println("连接MySQL失败");
}
try{
//创建Statement
Statement stmt=conn.createStatement();
//添加一条记录
String sql="insert into user(id,name,password) values(20140414,'bruce','1314')";
//执行sql语句
stmt.executeUpdate(sql);
}catch(SQLException e){
out.println("添加用户信息失败");
}
//关闭数据库
try{
if(stmt!=null){
stmt.close();
stmt=null;
}
if(conn!=null){
conn.close();
conn=null;
}
}catch(Exception e){
out.println("数据库关闭异常");
}
%>
其余操作只需更改一下sql语句即可。
当然还有关于ResultSet,PreparedStatement对象,不想写了,用到的话,就百度或Google吧。

MySQL uses a GPL license. 1) The GPL license allows the free use, modification and distribution of MySQL, but the modified distribution must comply with GPL. 2) Commercial licenses can avoid public modifications and are suitable for commercial applications that require confidentiality.

The situations when choosing InnoDB instead of MyISAM include: 1) transaction support, 2) high concurrency environment, 3) high data consistency; conversely, the situation when choosing MyISAM includes: 1) mainly read operations, 2) no transaction support is required. InnoDB is suitable for applications that require high data consistency and transaction processing, such as e-commerce platforms, while MyISAM is suitable for read-intensive and transaction-free applications such as blog systems.

In MySQL, the function of foreign keys is to establish the relationship between tables and ensure the consistency and integrity of the data. Foreign keys maintain the effectiveness of data through reference integrity checks and cascading operations. Pay attention to performance optimization and avoid common errors when using them.

There are four main index types in MySQL: B-Tree index, hash index, full-text index and spatial index. 1.B-Tree index is suitable for range query, sorting and grouping, and is suitable for creation on the name column of the employees table. 2. Hash index is suitable for equivalent queries and is suitable for creation on the id column of the hash_table table of the MEMORY storage engine. 3. Full text index is used for text search, suitable for creation on the content column of the articles table. 4. Spatial index is used for geospatial query, suitable for creation on geom columns of locations table.

TocreateanindexinMySQL,usetheCREATEINDEXstatement.1)Forasinglecolumn,use"CREATEINDEXidx_lastnameONemployees(lastname);"2)Foracompositeindex,use"CREATEINDEXidx_nameONemployees(lastname,firstname);"3)Forauniqueindex,use"CREATEU

The main difference between MySQL and SQLite is the design concept and usage scenarios: 1. MySQL is suitable for large applications and enterprise-level solutions, supporting high performance and high concurrency; 2. SQLite is suitable for mobile applications and desktop software, lightweight and easy to embed.

Indexes in MySQL are an ordered structure of one or more columns in a database table, used to speed up data retrieval. 1) Indexes improve query speed by reducing the amount of scanned data. 2) B-Tree index uses a balanced tree structure, which is suitable for range query and sorting. 3) Use CREATEINDEX statements to create indexes, such as CREATEINDEXidx_customer_idONorders(customer_id). 4) Composite indexes can optimize multi-column queries, such as CREATEINDEXidx_customer_orderONorders(customer_id,order_date). 5) Use EXPLAIN to analyze query plans and avoid

Using transactions in MySQL ensures data consistency. 1) Start the transaction through STARTTRANSACTION, and then execute SQL operations and submit it with COMMIT or ROLLBACK. 2) Use SAVEPOINT to set a save point to allow partial rollback. 3) Performance optimization suggestions include shortening transaction time, avoiding large-scale queries and using isolation levels reasonably.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

Dreamweaver CS6
Visual web development tools

SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.

SublimeText3 Linux new version
SublimeText3 Linux latest version

SublimeText3 Mac version
God-level code editing software (SublimeText3)
