通过使用COM技术,我们用微软Office应用程序能够建立很多应用程序扩展,但是Java开发人员却无法享受它带来的便利--除非他们拥有方便的Java访问COM的途径(Java-to-COM桥)。使用JCom的时候,你可以在Java中控制几乎所有的COM对象,而且它还带有一些用于Excel的强大的辅助类。
在你每次编写用HTML表格样式或Java表格对象显示数据的应用程序的时候,通常都需要带有"导出到Excel"功能。那么头疼的问题就出现了。怎么样实现这种功能呢?在HTML中显示的可以在Office 2003中处理吗?没有这么好!你还必须支持Office 97!
你只能去找一个符合当前需求的工具了,但是接着收到更多的要求了。"这能在Word中做到吗?Powerpoint能做到吗?能不能用调制解调器拨号到远程服务器上并发布数据?Java无法实现这些功能是什么意思啊?Java可以实现任何功能。"
感谢作为Java和COM桥梁的框架组件,它使你在遇到这些情况的时候都可以回答"Yes"。Java-COM桥梁使你能够根据自己的需要操作Windows组件--以前这是VB、C++和.NET开发人员的领地。你通过实现一个与DCOM后端(back end)对话的Java前端(front end),可以远离端对端(end-to-end)的COM系统。在本文的末尾,你可以使用其中一个Java-to-COM桥:它可以被命名为JCom。
Excel基础知识
开始之前,你需要首先从Sourceforge网站下载API。它包含了JCom所使用的Java类的所有源代码、C++代码和JCom用于配置Java和COM的编译好的DLL。把这个DLL放到你的Java主目录的/bin/目录下面,否则会出现问题。同时,为了不出现问题,还要正确地设置JAVA_HOME环境变量。JCom的大多数文档目前都是用日语写的,但是翻译工作正在进行中,因此以后会有些改进的。
下载和安装过程完成以后,用列表1中的代码试一试。这段代码会建立到Excel的JCom接口,并把"Hello World"写入第一个单元格中。你可以看到如图1所示的结果。尽管JCom是一个通用的COM类库,但是还是带有很多用于Excel的辅助类,这是因为Excel可能是最常用的自动化COM应用程序。这些辅助类可以为我们节省很多时间,它们使JCOM成为一个更好的类库了。
列表1:开始使用JCOM和Excel
import jp.ne.so_net.ga2.no_ji.jcom.excel8.*;
import jp.ne.so_net.ga2.no_ji.jcom.*;
public class testSimple
{
public static void main(String[] args) throws Exception {
ReleaseManager rm = new ReleaseManager();
try {
System.out.println("EXCEL is Starting...");
ExcelApplication excel = new ExcelApplication(rm);
excel.Visible(true);
ExcelWorkbooks xlBooks = excel.Workbooks();
ExcelWorkbook xlBook = xlBooks.Add();
ExcelWorksheets xlSheets = xlBook.Worksheets();
ExcelWorksheet xlSheet = xlSheets.Item(1);
ExcelRange xlRange = xlSheet.Cells();
xlRange.Item(1,1).Value("Hello, World!" );
}
catch(Exception e) { e.printStackTrace(); }
finally { rm.release(); }
}
}

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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