H2是一个JAVA数据库.我们可以使用JDBC与此数据库进行交互.在本章中，我们将了解如何使用H2数据库创建JDBC连接以及如何使用H2数据库创建CRUD操作.
通常，创建JDBC连接有五个步骤.
第1步 : 注册JDBC数据库驱动程序.
Class.forName("org.h2.Driver");第2步 : 打开连接.
Connection conn = DriverManager.getConnection ("jdbc:h2:~/test", "sa","");第3步 : 创建语句.
Statement st = conn.createStatement();
第4步 : 执行语句并接收Resultset.
Stmt.executeUpdate("sql statement");第5步 : 关闭连接.
conn.close();
在继续创建完整程序之前，我们需要将 h2-1.4.192.jar文件添加到CLASSPATH.我们可以从文件夹 C:\Program Files(x86)\H2 \bin 中获取 jar .
创建表
在本例中，我们将为create table编写一个程序.考虑一个名为注册的表，其中包含以下字段.
| S.No | 列名 | 数据类型 | NOT NULL | 主键 |
|---|---|---|---|---|
| 1 | ID | 数字 | 是 | 是 |
| 2 | 首先 | Varchar(255) | 否 | 否 |
| 3 | 最后 | Varchar(255) | 否 | 否 |
| 4 | 年龄 | 数字 | 否 | 否 |
以下是名为 H2jdbcCreateDemo 的示例程序.
import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.Statement; public class H2jdbcCreateDemo { // JDBC driver name and database URL static final String JDBC_DRIVER = "org.h2.Driver"; static final String DB_URL = "jdbc:h2:~/test"; // Database credentials static final String USER = "sa"; static final String PASS = ""; public static void main(String[] args) { Connection conn = null; Statement stmt = null; try { // STEP 1: Register JDBC driver Class.forName(JDBC_DRIVER); //STEP 2: Open a connection System.out.println("Connecting to database..."); conn = DriverManager.getConnection(DB_URL,USER,PASS); //STEP 3: Execute a query System.out.println("Creating table in given database..."); stmt = conn.createStatement(); String sql = "CREATE TABLE REGISTRATION " + "(id INTEGER not NULL, " + " first VARCHAR(255), " + " last VARCHAR(255), " + " age INTEGER, " + " PRIMARY KEY ( id ))"; stmt.executeUpdate(sql); System.out.println("Created table in given database..."); // STEP 4: Clean-up environment 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("Goodbye!"); } }将上述程序保存到H2jdbcCreateDemo.java中.通过在命令提示符中执行以下命令来编译并执行上述程序.
\>javac H2jdbcCreateDemo.java \>java H2jdbcCreateDemo
上述命令产生以下输出.
Connecting to database... Creating table in given database... Created table in given database... Goodbye!
执行此操作后，我们可以检查使用H2 SQL接口创建的表.
插入记录
在这个例子中，我们将编写一个用于插入记录的程序.让我们将以下记录插入表注册.
| ID | First | Last | 年龄 |
|---|---|---|---|
| 100 | Zara | Ali | 18 |
| 101 | Mahnaz | Fatma | 25 |
| 102 | Zaid | Khan | 30 |
| 103 | Sumit | Mital | 28 |
以下是名为 H2jdbcInsertDemo 的示例程序.
import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.Statement; public class H2jdbcInsertDemo { // JDBC driver name and database URL static final String JDBC_DRIVER = "org.h2.Driver"; static final String DB_URL = "jdbc:h2:~/test"; // Database credentials static final String USER = "sa"; static final String PASS = ""; public static void main(String[] args) { Connection conn = null; Statement stmt = null; try{ // STEP 1: Register JDBC driver Class.forName(JDBC_DRIVER); // STEP 2: Open a connection System.out.println("Connecting to a selected database..."); conn = DriverManager.getConnection(DB_URL,USER,PASS); System.out.println("Connected database successfully..."); // STEP 3: Execute a query stmt = conn.createStatement(); String sql = "INSERT INTO Registration " + "VALUES (100, 'Zara', 'Ali', 18)"; stmt.executeUpdate(sql); sql = "INSERT INTO Registration " + "VALUES (101, 'Mahnaz', 'Fatma', 25)"; stmt.executeUpdate(sql); sql = "INSERT INTO Registration " + "VALUES (102, 'Zaid', 'Khan', 30)"; stmt.executeUpdate(sql); sql = "INSERT INTO Registration " + "VALUES(103, 'Sumit', 'Mittal', 28)"; stmt.executeUpdate(sql); System.out.println("Inserted records into the table..."); // STEP 4: Clean-up environment 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("Goodbye!"); } }将上述程序保存到H2jdbcInsertDemo.java中.通过在命令提示符中执行以下命令来编译并执行上述程序.
\>javac H2jdbcInsertDemo.java \>java H2jdbcInsertDemo
上述命令产生以下输出.
Connecting to a selected database... Connected database successfully... Inserted records into the table... Goodbye!
读取记录
在本例中，我们将编写一个用于读取记录的程序.让我们尝试从表注册中读取所有记录.
以下是一个名为 H2jdbcRecordDemo 的示例程序.
import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class H2jdbcReadDemo { // JDBC driver name and database URL static final String JDBC_DRIVER = "org.h2.Driver"; static final String DB_URL = "jdbc:h2:~/test"; // Database credentials static final String USER = "sa"; static final String PASS = ""; public static void main(String[] args) { Connection conn = null; Statement stmt = null; try { // STEP 1: Register JDBC driver Class.forName(JDBC_DRIVER); // STEP 2: Open a connection System.out.println("Connecting to database..."); conn = DriverManager.getConnection(DB_URL,USER,PASS); // STEP 3: Execute a query System.out.println("Connected database successfully..."); stmt = conn.createStatement(); String sql = "SELECT id, first, last, age FROM Registration"; ResultSet rs = stmt.executeQuery(sql); // STEP 4: 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 5: Clean-up environment rs.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("Goodbye!"); } }将上述程序保存到H2jdbcReadDemo.java中.通过在命令提示符中执行以下命令来编译并执行上述程序.
\>javac H2jdbcReadDemo.java \>java H2jdbcReadDemo
上述命令产生以下输出.
Connecting to a selected database... Connected database successfully... ID: 100, Age: 18, First: Zara, Last: Ali ID: 101, Age: 25, First: Mahnaz, Last: Fatma ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 28, First: Sumit, Last: Mittal Goodbye!
更新记录
在本例中，我们将编写一个程序来更新记录.让我们尝试阅读表格中的所有记录注册.
以下是一个名为 H2jdbcUpdateDemo 的示例程序.
import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class H2jdbcUpdateDemo { // JDBC driver name and database URL static final String JDBC_DRIVER = "org.h2.Driver"; static final String DB_URL = "jdbc:h2:~/test"; // Database credentials static final String USER = "sa"; static final String PASS = ""; public static void main(String[] args) { Connection conn = null; Statement stmt = null; try { // STEP 1: Register JDBC driver Class.forName(JDBC_DRIVER); // STEP 2: Open a connection System.out.println("Connecting to a database..."); conn = DriverManager.getConnection(DB_URL,USER,PASS); // STEP 3: Execute a query System.out.println("Connected database successfully..."); stmt = conn.createStatement(); String sql = "UPDATE Registration " + "SET age = 30 WHERE id in (100, 101)"; stmt.executeUpdate(sql); // Now you can extract all the records // to see the updated records sql = "SELECT id, first, last, age FROM Registration"; ResultSet rs = stmt.executeQuery(sql); 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); } rs.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("Goodbye!"); } }将上述程序保存到H2jdbcUpdateDemo.java中.通过在命令提示符中执行以下命令来编译并执行上述程序.
\>javac H2jdbcUpdateDemo.java \>java H2jdbcUpdateDemo
上述命令产生以下输出.
Connecting to a selected database... Connected database successfully... ID: 100, Age: 30, First: Zara, Last: Ali ID: 101, Age: 30, First: Mahnaz, Last: Fatma ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 28, First: Sumit, Last: Mittal Goodbye!
删除记录
在本例中，我们将编写一个程序来删除记录.让我们尝试从表注册中读取所有记录.
以下是一个名为 H2jdbcDeleteDemo 的示例程序.
import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class H2jdbcDeleteDemo { // JDBC driver name and database URL static final String JDBC_DRIVER = "org.h2.Driver"; static final String DB_URL = "jdbc:h2:~/test"; // Database credentials static final String USER = "sa"; static final String PASS = ""; public static void main(String[] args) { Connection conn = null; Statement stmt = null; try { // STEP 1: Register JDBC driver Class.forName(JDBC_DRIVER); // STEP 2: Open a connection System.out.println("Connecting to database..."); conn = DriverManager.getConnection(DB_URL,USER,PASS); // STEP 3: Execute a query System.out.println("Creating table in given database..."); stmt = conn.createStatement(); String sql = "DELETE FROM Registration " + "WHERE id = 101"; stmt.executeUpdate(sql); // Now you can extract all the records // to see the remaining records sql = "SELECT id, first, last, age FROM Registration"; ResultSet rs = stmt.executeQuery(sql); 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); } rs.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("Goodbye!"); } }将上述程序保存到H2jdbcDeleteDemo.java中.通过在命令提示符中执行以下命令来编译并执行上述程序.
\>javac H2jdbcDeleteDemo.java \>java H2jdbcDeleteDemo
上述命令产生以下输出.
Connecting to a selected database... Connected database successfully... ID: 100, Age: 30, First: Zara, Last: Ali ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 28, First: Sumit, Last: Mittal Goodbye!