通过类的java sql连接

我有以下代码：

import java.sql.*; import java.net.*; public class binsz { public void dbConnect(String db_connect_string, String username, String password) { try { Class.forName("net.sourceforge.jtds.jdbc.Driver"); Connection conn = DriverManager.getConnection(db_connect_string, username, password); // System.out.println("connected"); } catch (Exception e) { e.printStackTrace(); } } public void dbQuery(String query) { try { Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery(query); } catch (Exception e) { e.printStackTrace(); } } public static void main(String[] args) throws Exception { String db_name = "sqlserver.local"; String username = "sa"; String password = "passwordforsa"; String connection = "jdbc:jtds:sqlserver://" + db_name; Connection conn = null; binsz db = new binsz(); db.dbConnect(connection, username, password); String query = "SELECT TOP 2 * FROM aux..table_name"; db.dbQuery(query); } } 

并在编译时出错：

 binsz.java:20: cannot find symbol symbol : variable conn location: class sip_bins Statement stmt = conn.createStatement(); ^ 1 error 

我怎样才能使用binsz db = new binsz(); 执行查询并检索它的值。

谢谢

PS：与数据库的连接正在工作..（如果我取消注释该行，则打印“已连接”）

Answer 1

这是非常糟糕的代码 – 没有写的。 你有很多工作要做。

我建议你学习这个并抛弃你的代码：

 package persistence; import java.sql.*; import java.util.*; /** * util.DatabaseUtils * User: Michael * Date: Aug 17, 2010 * Time: 7:58:02 PM */ public class DatabaseUtils { private static final String DEFAULT_DRIVER = "oracle.jdbc.driver.OracleDriver"; private static final String DEFAULT_URL = "jdbc:oracle:thin:@host:1521:database"; private static final String DEFAULT_USERNAME = "username"; private static final String DEFAULT_PASSWORD = "password"; /* private static final String DEFAULT_DRIVER = "org.postgresql.Driver"; private static final String DEFAULT_URL = "jdbc:postgresql://localhost:5432/party"; private static final String DEFAULT_USERNAME = "pgsuper"; private static final String DEFAULT_PASSWORD = "pgsuper"; */ /* private static final String DEFAULT_DRIVER = "com.mysql.jdbc.Driver"; private static final String DEFAULT_URL = "jdbc:mysql://localhost:3306/party"; private static final String DEFAULT_USERNAME = "party"; private static final String DEFAULT_PASSWORD = "party"; */ public static void main(String[] args) { long begTime = System.currentTimeMillis(); String driver = ((args.length > 0) ? args[0] : DEFAULT_DRIVER); String url = ((args.length > 1) ? args[1] : DEFAULT_URL); String username = ((args.length > 2) ? args[2] : DEFAULT_USERNAME); String password = ((args.length > 3) ? args[3] : DEFAULT_PASSWORD); Connection connection = null; try { connection = createConnection(driver, url, username, password); DatabaseMetaData meta = connection.getMetaData(); System.out.println(meta.getDatabaseProductName()); System.out.println(meta.getDatabaseProductVersion()); String sqlQuery = "SELECT PERSON_ID, FIRST_NAME, LAST_NAME FROM PERSON ORDER BY LAST_NAME"; System.out.println("before insert: " + query(connection, sqlQuery, Collections.EMPTY_LIST)); connection.setAutoCommit(false); String sqlUpdate = "INSERT INTO PERSON(FIRST_NAME, LAST_NAME) VALUES(?,?)"; List parameters = Arrays.asList("Foo", "Bar"); int numRowsUpdated = update(connection, sqlUpdate, parameters); connection.commit(); System.out.println("# rows inserted: " + numRowsUpdated); System.out.println("after insert: " + query(connection, sqlQuery, Collections.EMPTY_LIST)); } catch (Exception e) { rollback(connection); e.printStackTrace(); } finally { close(connection); long endTime = System.currentTimeMillis(); System.out.println("wall time: " + (endTime - begTime) + " ms"); } } public static Connection createConnection(String driver, String url, String username, String password) throws ClassNotFoundException, SQLException { Class.forName(driver); if ((username == null) || (password == null) || (username.trim().length() == 0) || (password.trim().length() == 0)) { return DriverManager.getConnection(url); } else { return DriverManager.getConnection(url, username, password); } } public static void close(Connection connection) { try { if (connection != null) { connection.close(); } } catch (SQLException e) { e.printStackTrace(); } } public static void close(Statement st) { try { if (st != null) { st.close(); } } catch (SQLException e) { e.printStackTrace(); } } public static void close(ResultSet rs) { try { if (rs != null) { rs.close(); } } catch (SQLException e) { e.printStackTrace(); } } public static void rollback(Connection connection) { try { if (connection != null) { connection.rollback(); } } catch (SQLException e) { e.printStackTrace(); } } public static List> map(ResultSet rs) throws SQLException { List> results = new ArrayList>(); try { if (rs != null) { ResultSetMetaData meta = rs.getMetaData(); int numColumns = meta.getColumnCount(); while (rs.next()) { Map row = new HashMap(); for (int i = 1; i <= numColumns; ++i) { String name = meta.getColumnName(i); Object value = rs.getObject(i); row.put(name, value); } results.add(row); } } } finally { close(rs); } return results; } public static List> query(Connection connection, String sql, List 

Answer 2

Connection conn当前位于方法dbConnect中的Connection conn声明为实例变量。 您收到此错误，因为conn在方法dbQuery是未知的。

Answer 3

你应该连接一个实例变量this.conn = DriverManager... 我还建议使用一个良好的连接池。

还记得在完成它们之后关闭语句，结果集和连接。

UPDATE

 try { ... } finally { if (rs != null) rs.close(); if (st != null) st.close(); //if (conn != null) conn.close(); // depends on wheter you need it again, or whil retrieve a new one } 

Answer 4

什么是骗局？

  Statement stmt = conn.createStatement(); 

在方法中

 public void dbQuery(String query) 

如果希望类的多个方法访问它，则需要将conn声明为实例变量。

Answer 5

你有：

 public void dbConnect(String db_connect_string, String username, String password) 

和电话：

 db.dbConnect(connection, username, password); 

您应该将其更改为：

 public void dbConnect(Connection conn, String username, String password) { ... conn = DriverManager.getConnection(db_connect_string, username, password); ... } 

和用法：

 db.dbConnect(conn, username, password); 

您还应该将方法的签名更改为：

 public void dbQuery(String query, Connection conn); 

和用途：

 db.dbQuery(query, conn);