Tomcat
一、前言
对于初学者来说,要执行JSP和Servlet,Tomcat是一个很不错的选择,。Tomcat是Apache组织的产品,sun公司对它的支持也相当不错。
二、下载,安装
下载地址为JAVA官方站点:jakarta.apache.org,国内也比较多。
从这个地址可以下载:http://jakarta.apache.org/builds/tomcat/release/,我下载的是Tomcat32b4版本。
下载完,解压到一个目录,我这里用F:\tomcat32b4作为例子。
三、配置
桌面上选择“我的电脑”(右键)
高级
环境变量
在“系统变量”--->“新建”
在变量名中输入:JAVA_HOME,变量值中输入:F:\JDK13然后确定;
在“系统变量”--->“新建”
在变量名中输入:TOMCAT_HOME,变量值中输入:F:\tomcat32b4然后确定;
好了,配置完了,要重新启动计算机后,环境变量才能有效的。
注意,对于Tomcat其他设置,如果没有必要,是可以不改的,我这里讲的都是最简单而可行的方法,如果对你的改动没有把握,还是建议不要改动。
四、测试
(1)启动tomcat:
在F:\tomcat32b4\bin下有一个:startup.bat,运行它,将出现一个Dos窗口。
(2)浏览
在浏览器中输入:http://localhost:8080/看看有什么效果(Tomcat默认端口为8080,在不冲突的前提下,你可以改动的),是不是可以看到一只可爱的小猫(其实,我个人认为,无论从颜色还是样子,更象一只老虎)
(3)运行
在这个页面有JSP Examples和 Servlet Examples, 好了,自己测试运行它们吧。
(4)退出tomcat
在F:\tomcat32b4\bin下有一个:shutdown.bat,运行它,将关闭Dos窗口(如果坚持直接关闭这个DOS窗口也是可以的,但是,既然有这个shutdown.bat,应该有它存在的理由)。

ACID attributes include atomicity, consistency, isolation and durability, and are the cornerstone of database design. 1. Atomicity ensures that the transaction is either completely successful or completely failed. 2. Consistency ensures that the database remains consistent before and after a transaction. 3. Isolation ensures that transactions do not interfere with each other. 4. Persistence ensures that data is permanently saved after transaction submission.

MySQL is not only a database management system (DBMS) but also closely related to programming languages. 1) As a DBMS, MySQL is used to store, organize and retrieve data, and optimizing indexes can improve query performance. 2) Combining SQL with programming languages, embedded in Python, using ORM tools such as SQLAlchemy can simplify operations. 3) Performance optimization includes indexing, querying, caching, library and table division and transaction management.

MySQL uses SQL commands to manage data. 1. Basic commands include SELECT, INSERT, UPDATE and DELETE. 2. Advanced usage involves JOIN, subquery and aggregate functions. 3. Common errors include syntax, logic and performance issues. 4. Optimization tips include using indexes, avoiding SELECT* and using LIMIT.

MySQL is an efficient relational database management system suitable for storing and managing data. Its advantages include high-performance queries, flexible transaction processing and rich data types. In practical applications, MySQL is often used in e-commerce platforms, social networks and content management systems, but attention should be paid to performance optimization, data security and scalability.

The relationship between SQL and MySQL is the relationship between standard languages and specific implementations. 1.SQL is a standard language used to manage and operate relational databases, allowing data addition, deletion, modification and query. 2.MySQL is a specific database management system that uses SQL as its operating language and provides efficient data storage and management.

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB


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