2、JDBC-CURD

添加，修改，删除

package test.jdbc;

import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

public class CURDTest {

    private Connection conn;
    private Statement statement;
    private ResultSet result;

    @BeforeEach
    public void start() throws Exception {
        Properties properties = new Properties();
        InputStream in = this.getClass().getClassLoader().getResourceAsStream("jdbc.properties");
        properties.load(in);

        String driver = properties.getProperty("driver");
        String jdbcUrl = properties.getProperty("jdbcUrl");
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");

        Class.forName(driver);

        conn = DriverManager.getConnection(jdbcUrl, user, password);
    }

    @AfterEach
    public void end() throws Exception {
        if (result != null) {
            result.close();
        }
        if (statement != null) {
            statement.close();
        }
        if (conn != null) {
            conn.close();
        }
    }

    /**
     * 通过 JDBC 向指定的数据表中插入一条记录
     *
     * Statement: 用于执行 SQL 语句的对象
     * SQL 可以是 INSERT、UPDATE、DELETE. 不能为 SELECT
     * Connection、Statement 都是应用程序和数据库服务器的连接资源. 使用后要关闭
     */
    @Test
    public void testStatement() throws Exception {
        try {
            statement = conn.createStatement();
            // SQL 语句
            statement.executeUpdate("INSERT INTO user (name, age) VALUES('SWT', 22)");

            // SQL 占位符
            PreparedStatement preparedStatement = conn.prepareStatement("INSERT INTO user (name, age) VALUES(?, ?)");
            preparedStatement.setObject(1,"WC");
            preparedStatement.setObject(2,23);
            preparedStatement.executeUpdate();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

添加数据时返回主键

@Test
public void testGetKeyValue() {
    try {
        String sql = "INSERT INTO user (name, age) VALUES(?, ?)";
        // 使用重载的 prepareStatement(sql, flag)
        PreparedStatement preparedStatement = conn.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS);
        preparedStatement.setObject(1, "ABCDE");
        preparedStatement.setObject(2, 22);
        preparedStatement.execute();
        // 通过 getGeneratedKeys() 获取包含了新生成的主键的 ResultSet 对象
        // 在 ResultSet 中只有一列 GENERATED_KEY, 用于存放新生成的主键值
        ResultSet rs = preparedStatement.getGeneratedKeys();
        if(rs.next()){
            System.out.println(rs.getInt("GENERATED_KEY"));
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

查询

/**
 * ResultSet: 结果集. 封装了使用 JDBC 进行查询的结果
 * 调用 Statement 对象的 executeQuery(sql) 可以得到 ResultSet 结果集
 * 调用 ResultSet 的 next() 方法检测下一行是否有效. 若有效该方法返回 true, 且指针下移
 * 当指针对位到一行时, 可以通过调用 getXxx(index) 或 getXxx(columnName) 得到数据
 */
@Test
public void testResultSet() {
    try {
        // 获取 Statement
        statement = conn.createStatement();
        // SQL
        String sql = "SELECT * FROM user";
        // 执行查询, 得到 ResultSet
        result = statement.executeQuery(sql);
        // 处理 ResultSet
        while (result.next()) {
            int id = result.getInt(1);
            String name = result.getString("name");
            int age = result.getInt(3);
            System.out.println(id + "\t" + name + "\t" + age);
        }

        PreparedStatement preparedStatement = conn.prepareStatement("SELECT * FROM user where id = ?");
        preparedStatement.setObject(1,1);
        result = preparedStatement.executeQuery();
        while (result.next()) {
            int id = result.getInt(1);
            String name = result.getString("name");
            int age = result.getInt(3);
            System.out.println(id + "\t" + name + "\t" + age);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

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