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下面展示了连接SQL Server数据库的整个流程：
- 加载数据库驱动
- 建立数据库连接
- 执行SQL语句
- 处理结果
- 关闭连接
在连接之前，前提是确保数据库成功的下载，创建，配置好账号密码。
运行成功的代码：
import java.sql.*;public class sqlserverConnection {//驱动private static String cxDriver = "com.microsoft.sqlserver.jdbc.SQLServerDriver";//连接地址private static String cxUrl = "jdbc:sqlserver://172.16.100.1:1433;databaseName=abc;encrypt=false";//用户名private static String cxUser = "abc";//用户密码:数据库的密码private static String cxPassword = "abc";public static void main(String[] args) {try{Class.forName(cxDriver); //加载sqlserver的驱动类System.out.println("加载SQLServer驱动类成功!");}catch(ClassNotFoundException a){System.out.println("加载SQLServer驱动失败!");a.printStackTrace();}Connection dbcon=null; //处理与特定数据库的连接try{dbcon=DriverManager.getConnection(cxUrl,cxUser,cxPassword);System.out.println("数据库连接成功!");dbcon.close();}catch(SQLException e){System.out.println("数据库连接失败!");e.printStackTrace();}}}报错：
Exception in thread "main" java.lang.UnsupportedClassVersionError: com/microsoft/sqlserver/jdbc/SQLServerDriver has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0at java.lang.ClassLoader.defineClass1(Native Method)at java.lang.ClassLoader.defineClass(ClassLoader.java:763)at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)at java.net.URLClassLoader.access$100(URLClassLoader.java:74)at java.net.URLClassLoader$1.run(URLClassLoader.java:369)at java.net.URLClassLoader$1.run(URLClassLoader.java:363)at java.security.AccessController.doPrivileged(Native Method)at java.net.URLClassLoader.findClass(URLClassLoader.java:362)at java.lang.ClassLoader.loadClass(ClassLoader.java:424)at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)at java.lang.ClassLoader.loadClass(ClassLoader.java:357)at java.lang.Class.forName0(Native Method)at java.lang.Class.forName(Class.java:264)at timeunit_test.sqlserverConnection.main(sqlserverConnection.java:17)
问题在于用较高版本的jdk编译的class文件在低版本的JVM上运行所导致的，通俗讲就是编译运行版本不匹配。
可惜我不是
看下jar包目录下是否存在多余的，不需要的版本，去除
我第一次jre8,jre11版本的都导入了，导致驱动加载失败
使用cmd java -version 查看java javac版本 是否都匹配
加载驱动成功，但是连接又失败了
com.microsoft.sqlserver.jdbc.SQLServerException: "encrypt" property is set to "true" and "trustServerCertificate" property is set to "false" but the driver could not establish a secure connection to SQL Server by using Secure Sockets Layer (SSL) encryption: Error: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target. ClientConnectionId:f903a939-f589-4052-89f8-580442a86a1bat com.microsoft.sqlserver.jdbc.SQLServerConnection.terminate(SQLServerConnection.java:4026)at com.microsoft.sqlserver.jdbc.TDSChannel.enableSSL(IOBuffer.java:1954)at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectHelper(SQLServerConnection.java:3552)at com.microsoft.sqlserver.jdbc.SQLServerConnection.login(SQLServerConnection.java:3172)at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectInternal(SQLServerConnection.java:3014)at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(SQLServerConnection.java:1836)at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(SQLServerDriver.java:1246)at java.sql.DriverManager.getConnection(DriverManager.java:664)at java.sql.DriverManager.getConnection(DriverManager.java:247)at timeunit_test.sqlserverConnection.main(sqlserverConnection.java:26)
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target...
这个问题最有效的办法是在连接地址Url后面加上encrypt=false。
执行SQL语句:
Statement statement = connection.createStatement();
String sql = "SELECT * FROM mytable";
ResultSet resultSet = statement.executeQuery(sql);
上述代码中，statement对象用于执行SQL语句。sql是要执行的SQL语句，这里是一个简单的查询语句。executeQuery()方法用于执行查询语句，并返回一个ResultSet对象，用于获取查询结果。
处理结果
while (resultSet.next()) {int id = resultSet.getInt("id");String name = resultSet.getString("name");// 处理每一条查询结果
}
上述代码中，通过resultSet.next()方法判断是否还有下一条查询结果，然后使用getInt()和getString()等方法获取查询结果中的具体字段值。
关闭连接
resultSet.close();
statement.close();
connection.close();
上述代码中，分别关闭resultSet、statement和connection对象，释放相关资源。
参考大家的文档
https://blog.csdn.net/qq243920161/article/details/78971861
https://blog.csdn.net/m0_46669582/article/details/111685213
https://blog.csdn.net/qq_42759370/article/details/103350930
https://blog.csdn.net/qq_37917691/article/details/108262286
https://blog.csdn.net/Green_Hand_is_me/article/details/122272151
https://blog.csdn.net/qq_45835014/article/details/128268932
https://blog.csdn.net/qq_51391437/article/details/121051234