海兰我有以下代码：
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);
}
}
它在编译它给出了一个错误：
binsz.java:20: cannot find symbol
symbol : variable conn
location: class sip_bins
Statement stmt = conn.createStatement();
^
1 error
我如何使用binsz db = new binsz(); 执行查询和检索它的值。
谢谢
PS：到数据库的连接是否正常工作。（它打印“连接”如果我取消注释行）..
这是很可怕的代码 - 无用的写入。 你有很多工作要做。
我建议你学习这一点，把你的代码走：
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<String, Object>> map(ResultSet rs) throws SQLException {
List<Map<String, Object>> results = new ArrayList<Map<String, Object>>();
try {
if (rs != null) {
ResultSetMetaData meta = rs.getMetaData();
int numColumns = meta.getColumnCount();
while (rs.next()) {
Map<String, Object> row = new HashMap<String, Object>();
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<Map<String, Object>> query(Connection connection, String sql, List<Object> parameters) throws SQLException {
List<Map<String, Object>> results = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
ps = connection.prepareStatement(sql);
int i = 0;
for (Object parameter : parameters) {
ps.setObject(++i, parameter);
}
rs = ps.executeQuery();
results = map(rs);
} finally {
close(rs);
close(ps);
}
return results;
}
public static int update(Connection connection, String sql, List<Object> parameters) throws SQLException {
int numRowsUpdated = 0;
PreparedStatement ps = null;
try {
ps = connection.prepareStatement(sql);
int i = 0;
for (Object parameter : parameters) {
ps.setObject(++i, parameter);
}
numRowsUpdated = ps.executeUpdate();
} finally {
close(ps);
}
return numRowsUpdated;
}
}
声明Connection conn这是目前在该方法dbConnect为一个实例变量。 你得到这个错误，因为conn是在方法未知dbQuery 。
你应该让连接的实例变量this.conn = DriverManager... 。 我也建议使用一个很好的连接池。
还记得你与他们完成后，关闭您的语句，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
}
这到底是怎么conn将？
Statement stmt = conn.createStatement();
在该方法中
public void dbQuery(String query)
你需要，如果你希望你的类的多个方法来访问它宣布康涅狄格州作为一个实例变量。
你有：
public void dbConnect(String db_connect_string, String username, String password)
和呼叫：
db.dbConnect(connection, username, password);
你应该将其更改为：
public void dbConnect(Connection conn, String username, String password) {
...
conn = DriverManager.getConnection(db_connect_string, username, password);
...
}
和使用：
db.dbConnect(conn, username, password);
你也应该改变你的方法的签名：
public void dbQuery(String query, Connection conn);
和用法：
db.dbQuery(query, conn);
