本文章教程中將演示如何創(chuàng)建一個簡單的JDBC應(yīng)用程序的示例。 這將顯示如何打開數(shù)據(jù)庫連接,執(zhí)行SQL查詢并顯示結(jié)果。
這個示例代碼中涉及所有步驟,一些步驟將在本教程的后續(xù)章節(jié)中進(jìn)行說明。
構(gòu)建JDBC應(yīng)用程序涉及以下六個步驟 -
import java.sql.*
就足夠了。DriverManager.getConnection()
方法創(chuàng)建一個Connection
對象,它表示與數(shù)據(jù)庫的物理連接。Statement
的對象來構(gòu)建和提交SQL語句到數(shù)據(jù)庫。ResultSet.getXXX()
方法從結(jié)果集中檢索數(shù)據(jù)。當(dāng)您以后需要創(chuàng)建自己的JDBC應(yīng)用程序時,可將此示例可以作為模板使用,建議您收藏好此網(wǎng)頁。
此示例代碼是基于上一章完成的環(huán)境和數(shù)據(jù)庫設(shè)置之后編寫的。
在FirstExample.java (F:\worksp\jdbc\FirstExample.java)中復(fù)制并粘貼以下示例,編譯并運(yùn)行如下 -
//STEP 1. Import required packages
import java.sql.*;
public class FirstExample {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost/emp";
// Database credentials
static final String USER = "root";
static final String PASS = "123456";
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try{
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL,USER,PASS);
//STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
String sql;
sql = "SELECT id, first, last, age FROM Employees";
ResultSet rs = stmt.executeQuery(sql);
//STEP 5: Extract data from result set
while(rs.next()){
//Retrieve by column name
int id = rs.getInt("id");
int age = rs.getInt("age");
String first = rs.getString("first");
String last = rs.getString("last");
//Display values
System.out.print("ID: " + id);
System.out.print(", Age: " + age);
System.out.print(", First: " + first);
System.out.println(", Last: " + last);
}
//STEP 6: Clean-up environment
rs.close();
stmt.close();
conn.close();
}catch(SQLException se){
//Handle errors for JDBC
se.printStackTrace();
}catch(Exception e){
//Handle errors for Class.forName
e.printStackTrace();
}finally{
//finally block used to close resources
try{
if(stmt!=null)
stmt.close();
}catch(SQLException se2){
}// nothing we can do
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}//end finally try
}//end try
System.out.println("There are so thing wrong!");
}//end main
}//end FirstExample
把上面代碼存放到 F:\worksp\jdbc\FirstExample.java 文件中,并創(chuàng)建一個目錄:F:\worksp\jdbc\libs,下載 mysql-connector-java-5.1.40-bin.jar
放入到F:\worksp\jdbc\libs 目錄中。
下載地址:http://downloads.mysql.com/archives/c-j/
使用命令行編譯Java程序并加載指定目錄中的Jar包(mysql-connector-java-5.1.40-bin.jar
):
F:\worksp\jdbc> javac -Djava.ext.dirs=./libs FirstExample.java
##-- 或者
F:\worksp\jdbc> javac -Djava.ext.dirs=F:\worksp\jdbc\libs FirstExample.java
編譯上面代碼后,得到以下結(jié)果 -
## F:\worksp\jdbc>javac -Djava.ext.dirs=./libs FirstExample.java
## 運(yùn)行程序 -
F:\worksp\jdbc>java -Djava.ext.dirs=./libs FirstExample
Connecting to database...
Tue May 30 22:43:18 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Creating statement...
ID: 100, Age: 28, First: Max, Last: Su
ID: 101, Age: 25, First: Wei, Last: Wang
ID: 102, Age: 30, First: Xueyou, Last: Zhang
ID: 103, Age: 28, First: Jack, Last: Ma
There are so thing wrong!
F:\worksp\jdbc>
完整的執(zhí)行過程如下 -
或者使用 Eclipse
或其它IDE創(chuàng)建代碼執(zhí)行。