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了解JDBC

發(fā)布時(shí)間：2025/3/21 编程问答 20 豆豆

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?JDBC Intro

　　JDBC stands for Java Database Connectivity. Java與各種數(shù)據(jù)庫連接的標(biāo)準(zhǔn)Java api.

The JDBC library includes APIs for each of the tasks commonly associated with database usage:
　　? Making a connection to a database

　　? Creating SQL or MySQL statements

　　? Executing that SQL or MySQL queries in the database

　　? Viewing & Modifying the resulting records

jdbc API由以下兩個(gè)package構(gòu)成：

java.sql
javax.sql

Package java.sql Description

Provides the API for accessing and processing data stored in a data source (usually a relational database) using the Java^TM?programming language. This API includes a framework whereby different drivers can be installed dynamically to access different data sources. Although the JDBC^TM?API is mainly geared to passing SQL statements to a database, it provides for reading and writing data from any data source with a tabular format. The reader/writer facility, available through the?javax.sql.RowSet?group of interfaces, can be customized to use and update data from a spread sheet, flat file, or any other tabular data source.

Package javax.sql Description

Provides the API for server side data source access and processing from the Java^TM?programming language. This package supplements the?java.sql?package and, as of the version 1.4 release, is included in the Java Platform, Standard Edition (Java SE^TM). It remains an essential part of the Java Platform, Enterprise Edition (Java EE^TM).

　　The?javax.sql?package provides for the following:

The?DataSource?interface as an alternative to the?DriverManager?for establishing a connection with a data source

Connection pooling and Statement pooling

Distributed transactions

Rowsets

　　Applications use the?DataSource?and?RowSet?APIs directly, but the connection pooling and distributed transaction APIs are used internally by the middle-tier infrastructure.

JDBC API主要包括（斜體代表接口，需驅(qū)動(dòng)程序提供者來具體實(shí)現(xiàn)）：

DriverManager：負(fù)責(zé)加載各種不同驅(qū)動(dòng)程序（Driver），并根據(jù)不同的請(qǐng)求，向調(diào)用者返回相應(yīng)的數(shù)據(jù)庫連接（Connection）。
Driver：驅(qū)動(dòng)程序，會(huì)將自身加載到DriverManager中去，并處理相應(yīng)的請(qǐng)求并返回相應(yīng)的數(shù)據(jù)庫連接（Connection）。
Connection：數(shù)據(jù)庫連接，負(fù)責(zé)進(jìn)行與數(shù)據(jù)庫間的通訊，SQL執(zhí)行以及事務(wù)處理都是在某個(gè)特定Connection環(huán)境中進(jìn)行的。可以產(chǎn)生用以執(zhí)行SQL的Statement。
Statement：用以執(zhí)行SQL查詢和更新（針對(duì)靜態(tài)SQL語句和單次執(zhí)行）。
PreparedStatement：用以執(zhí)行包含動(dòng)態(tài)參數(shù)的SQL查詢和更新（在服務(wù)器端編譯，允許重復(fù)執(zhí)行以提高效率）。
CallableStatement：用以調(diào)用數(shù)據(jù)庫中的存儲(chǔ)過程。
SQLException：代表在數(shù)據(jù)庫連接的建立和關(guān)閉和SQL語句的執(zhí)行過程中發(fā)生了例外情況（即錯(cuò)誤）。

指定driver的方法(old)：

Class.forName("com.mysql.jdbc.Driver"); // method 1new com.mysql.jdbc.Driver() ; //method 2, mysql as an exmple, 創(chuàng)建driver對(duì)象，加載數(shù)據(jù)庫驅(qū)動(dòng)System.setProperty("jdbc.drivers","com.mysql.jdbc.Driver"); // method 3

注意JDBC 4.0 已不需要手動(dòng)注冊(cè)driver, JDBC文檔原文：

　　Applications no longer need to explictly load JDBC drivers using?Class.forName(). Existing programs which currently load JDBC drivers using?Class.forName()?will continue to work without modification.

　　JDBC 4.0 Drivers must include the file?META-INF/services/java.sql.Driver

?JDBC4.0 Example

　　mysql-connector-java:

<dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>6.0.4</version></dependency> View Code

Code Example

Driver: mysql-connector-java

1 /** 2 * Created by artificerPi on 2016/2/23. 3 * JDBC Program, create database 4 * 5 */ 6 7 // STEP 1. Import required packages 8 import java.sql.*; 9 10 public class JDBCExample { 11 // JDBC driver name and database URL 12 static final String JDBC_DRIVER="com.mysql.jdbc.Driver"; 13 static final String DB_URL="jdbc:mysql://localhost"; 14 15 // Database credentials 16 static final String USER ="root"; 17 static final String PASS="passw0rd"; 18 19 public static void main(String[] args){ 20 Connection conn = null; 21 Statement stmt = null; 22 23 try{ 24 //STEP2 : Register JDBC driver 25 Class.forName(JDBC_DRIVER); // load driver class 26 27 //STEP3 : Open a connection 28 System.out.println("Connecting to database..."); 29 conn = DriverManager.getConnection(DB_URL,USER,PASS); 30 31 // STEP 4: Execute a query 32 System.out.println("Creating statement ..."); 33 stmt = conn.createStatement(); 34 35 String sql; 36 sql="CREATE DATABASE STUDENTS"; 37 stmt.executeUpdate(sql); 38 System.out.println("Database created successfully..."); 39 }catch(SQLException se){ 40 //Handle errors for JDBC 41 se.printStackTrace(); 42 }catch (Exception e){ 43 // Handle errors for Class.forName 44 e.printStackTrace(); 45 }finally { 46 //STEP5: finally block used to close resources 47 try{ 48 if (stmt != null) 49 stmt.close(); 50 }catch (SQLException se2){// nothing we can do 51 }try{ 52 if(conn!=null) 53 conn.close(); 54 }catch (SQLException se){ 55 se.printStackTrace(); 56 }// end finally try 57 }// end try 58 System.out.println("GoodBye!"); 59 }//end main 60 }// end FirstExample

使用PreparedStatement

1 PreparedStatement ps = null; 2 ResultSet rs = null; 3 try { 4 ps = conn.prepareStatement("SELECT i.*, j.* FROM Omega i, Zappa j WHERE i = ? AND j = ?"); 5 // 使用問號(hào)作為參數(shù)的標(biāo)示 6 7 // 進(jìn)行參數(shù)設(shè)置 8 // 與大部分Java API中下標(biāo)的使用方法不同，字段的下標(biāo)從1開始，1代表第一個(gè)問號(hào) 9 // 當(dāng)然，還有其他很多針對(duì)不同類型的類似的PreparedStatement.setXXX()方法 10 ps.setString(1, "Poor Yorick"); 11 ps.setInt(2, 8008); 12 13 // 結(jié)果集 14 rs = ps.executeQuery(); 15 while (rs.next()) { 16 int numColumns = rs.getMetaData().getColumnCount(); 17 for (int i = 1; i <= numColumns; i++) { 18 // 與大部分Java API中下標(biāo)的使用方法不同，字段的下標(biāo)從1開始 19 // 當(dāng)然，還有其他很多的方式（ResultSet.getXXX()）獲取數(shù)據(jù) 20 System.out.println("COLUMN " + i + " = " + rs.getObject(i)); 21 } 22 } 23 } catch (SQLException e) { 24 // 異常處理 25 } finally { // 使用finally進(jìn)行資源釋放 26 try { 27 rs.close(); 28 ps.close(); 29 } catch (SQLException e) { 30 } // 異常處理：忽略close()時(shí)的錯(cuò)誤 31 }

事務(wù) Example

1 boolean autoCommitDefault = conn.getAutoCommit(); 2 try { 3 conn.setAutoCommit(false); 4 5 /* 在此基于有事務(wù)控制的conn執(zhí)行你的代碼 */ 6 7 conn.commit(); 8 } catch (Throwable e) { 9 try { 10 conn.rollback(); 11 } catch (Throwable ignore) { 12 } 13 throw e; 14 } finally { 15 try { 16 conn.setAutoCommit(autoCommitDefault); 17 } catch (Throwable ignore) { 18 } 19 } View Code

JDBC Cycle

參考：

　　http://www.tutorialspoint.com/jdbc/

　　https://docs.oracle.com/javase/8/docs/technotes/guides/jdbc/

　　https://zh.wikipedia.org/wiki/Java%E6%95%B0%E6%8D%AE%E5%BA%93%E8%BF%9E%E6%8E%A5

　　https://www.ntu.edu.sg/home/ehchua/programming/java/JDBC_Basic.html

轉(zhuǎn)載于:https://www.cnblogs.com/7explore-share/p/5927802.html

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