【正文】 , so programmers familiar with ODBC will find it very easy to learn JDBC. JDBC retains the basic design features of ODBC。39。 interface, which means that it is used to invoke (or ``call39。t have to worry about writing different applications to run on different platforms. The bination of Java and JDBC lets a programmer write it once and run it anywhere. Java, being robust, secure, easy to use, easy to understand, and automatically downloadable on a work, is an excellent language basis for database applications. What is needed is a way for Java applications to talk to a variety of different databases. JDBC is the mechanism for doing this. JDBC extends what can be done in Java. For example, with Java and the JDBC API, it is possible to publish a web page containing an applet that uses information obtained from a remote database. Or an enterprise can use JDBC to connect all its employees (even if they are using a conglomeration of Windows, Macintosh, and UNIX machines) to one or more internal databases via an intra. With more and more programmers using the Java programming language, the need for easy database access from Java is continuing to grow. MIS managers like the bination of Java and JDBC because it makes disseminating information easy and economical. Businesses can continue to use their installed databases and access information easily even if it is stored on different database management systems. Development time for new applications is short. Installation and version control are greatly simplified. A programmer can write an application or an update once, put it on the server, and everybody has access to the latest version. And for businesses selling information services, Java and JDBC offer a better way of getting out information updates to external customers. What Does JDBC Do? Simply put, JDBC makes it possible to do three things: 1. establish a connection with a database 2. send SQL statements 3. process the results. The following code fragment gives a basic example of these three steps: Connection con = ( jdbc:odbc:wombat, login, password)。第 2 類驅(qū)動(dòng)程序在直接的純 Java 驅(qū)動(dòng)程序還沒有上市前將會(huì)作為過渡方案來使用。通常，這是最為靈活的 JDBC 驅(qū)動(dòng)程序。因此，有關(guān)最新的信息，請(qǐng)查閱 JDBC 的網(wǎng)站，可通過從以下 URL 開始瀏覽找到： ? JDBC 驅(qū)動(dòng)程序的類型 我們目前所知曉的 JDBC 驅(qū)動(dòng)程序可分為以下四個(gè)種類： JDBCODBC 橋加 ODBC 驅(qū)動(dòng)程序： JavaSoft 橋產(chǎn)品利用 ODBC 驅(qū)動(dòng)程序提供 JDBC 訪問。驅(qū)動(dòng)程序開發(fā)人員可用 JDBC API 所帶的測(cè)試工具包來確定他們的驅(qū)動(dòng)程序是否符合這些標(biāo)準(zhǔn)。 轉(zhuǎn)義語法為幾個(gè)常見的 SQL 分歧提供了一種標(biāo)準(zhǔn)的 JDBC 語法。例如，并非所有的數(shù)據(jù)庫都支持儲(chǔ)存程序或外部連接，那些支持這一功能的數(shù)據(jù)庫又相互不一致。中間層的另一個(gè)好處是，用戶可以利用易于使用的高級(jí) API，而中間層將把它轉(zhuǎn)換為相應(yīng)的低級(jí)調(diào)用。這將需要一個(gè) JDBC 驅(qū)動(dòng) 程序來與所訪問的特定數(shù)據(jù)庫管理系統(tǒng)進(jìn)行通訊。它們之間最大的區(qū)別在于： JDBC以 Java 風(fēng)格與優(yōu)點(diǎn)為基礎(chǔ)并進(jìn)行優(yōu)化，因此更加易于使用。相反， JDBC 盡量保證簡(jiǎn)單功能的簡(jiǎn)便性，而同時(shí)在必要時(shí)允許使用高級(jí)功能。為什么 Java 不使用 ODBC？ 對(duì)這個(gè)問題的回答是： Java 可以使用 ODBC，但最好是在 JDBC 的幫助下以JDBCODBC 橋的形式使用。 隨著人們對(duì) JDBC 的興趣日益增漲，越來越多的開發(fā)人員一直在使用基于 JDBC 的工具，以使程序的編寫更加容易。相反，嵌入式 SQL 預(yù)處理器允許程序員將 SQL 語句直接與 Java 混在一起使用。 float f = getFloat(c)。程序員可只編寫一遍應(yīng)用程序或只更新一次，然后將它放到服務(wù)器上，隨后任何人就都可得到最新版本的應(yīng)用程序。 JDBC 擴(kuò)展了 Java 的功能。 有了 JDBC，向各種關(guān)系數(shù)據(jù)庫發(fā)送 SQL 語句就是一件很容 易的事。換言之，有了 JDBC API， 就不必為訪問 Sybase 數(shù)據(jù)庫專門寫一個(gè)程序，為訪問 Oracle 數(shù)據(jù)庫又專門寫一個(gè)程序，為訪問 Informix 數(shù)據(jù)庫又寫另一個(gè)程序，等等。例如，用 Java 和 JDBC API 可以發(fā)布含有 applet 的網(wǎng)頁，而該 applet 使用的信息可能來自遠(yuǎn)程數(shù)據(jù)庫。對(duì)于商務(wù)上的銷售信息服務(wù)， Java 和 JDBC 可為外部客戶提供獲取信息更新的更好方法。 } ? JDBC 是一種低級(jí) API ，是高級(jí) API 的基礎(chǔ) JDBC 是個(gè)“低級(jí)”接口，也就是說，它用于直接調(diào)用 SQL 命令。例如，可在 SQL 語句中使用 Java 變量，用以接受或提供 SQL 值。程序員也一直在編寫力圖使最終用戶對(duì)數(shù)據(jù)庫的訪問變得更為簡(jiǎn)單的應(yīng)用程序?，F(xiàn)在的問題已變成：“為什么需要 JDBC”？ 回答如下： ? ODBC 不適合直接在 Java 中使用，因?yàn)樗褂? C 語言接口。 ? 啟用“純 Java ”機(jī)制需要象 JDBC 這樣的 Java API。 最近， Microsoft 又引進(jìn)了 ODBC 之外的新 API： RDO、 ADO 和 OLE DB。用戶的 SQL 語句被送往數(shù)據(jù)庫中，而其結(jié)果將被送回給用戶。最后，許多情況下三層結(jié)構(gòu)可 提供一些性能上的好處。人們希望 SQL 中真正標(biāo)準(zhǔn)的那部份能夠進(jìn)行擴(kuò)展以包括越來越多的功能。例如，對(duì)日期文字和已儲(chǔ)存過程的調(diào)用都有轉(zhuǎn)義語法。 “符合 JDBC 標(biāo)準(zhǔn) TM” 表示提供者的 JDBC 實(shí)現(xiàn)已經(jīng)通過了 JavaSoft 提供的一致性測(cè)試。注意，必須將 ODBC 二進(jìn)制代碼（許多情況下還包括數(shù)據(jù)庫客戶機(jī)代碼）加載到使用該驅(qū)動(dòng)程序的每個(gè)客戶機(jī)上。有可能所有這種解決方案的提供者都提供適合于 Intra 用的產(chǎn)品。對(duì)第 2 類驅(qū)動(dòng)程序可能會(huì)有一些變種，這些變種要求有連接器，但通常這些是更加不可取的解決方案。 Statement stmt = ()。39。. More sophisticated mappings are also provided, for example, where rows of multiple tables are bined in a Java class. As interest in JDBC has grown, more developers have been working on JDBCbased tools to make building programs easier, as well. Programmers have also been writing applications that make accessing a database easier for the end user. For example, an application might present a menu of database tasks from which to choose. After a task is selected, the application presents prompts and blanks for filling in information needed to carry out the selected task. With the requested input typed in, the application then automatically invokes the necessary SQL mands. With the help of such an application, users can perform database tasks even when they have little or no knowledge of SQL syntax. JDBC versus ODBC and other APIs At this point, Microsoft39。 in fact, both interfaces are based on the X/Open SQL CLI (Call Level Interface). The big difference is that JDBC builds on and reinforces the style and virtues of Java, and, of course, it is easy to use. More recently, Microsoft has introduced new APIs beyond ODBC: RDO, ADO, DAO, and OLE DB. These designs move in the same direction as JDBC in many ways, for example, in being objectoriented interfaces to databases based on classes that can be implemented on ODBC. However, we did not see functionality in any of these interfaces pelling enough to make them an alternative basis to ODBC, especially with the ODBC driver market wellestablished. Mostly they represent a thin veneer on ODBC. This is not to say that JDBC does not need to evolve from the initial release described in this book。39。 rule around the party discipline, disciplinary ruler requirements, listed as negative list, focusing on vertical gauge, draw the party anizations and Party members do not touch the bottom line . Here, the main from four square face two party rules of interpretation: the first part intro