在Resultset Java中执行访问查询
我试图对MDB文件执行计数查询,并希望将其存储到局部变量 我得到错误类型不匹配:如果直接分配输出,则无法从布尔值转换为int 在尝试使用结果集时,我得到了类似的错误以及类型不匹配:无法从布尔值转换为结果集 代码如下:在Resultset Java中执行访问查询,java,eclipse,ms-access,Java,Eclipse,Ms Access,我试图对MDB文件执行计数查询,并希望将其存储到局部变量 我得到错误类型不匹配:如果直接分配输出,则无法从布尔值转换为int 在尝试使用结果集时,我得到了类似的错误以及类型不匹配:无法从布尔值转换为结果集 代码如下: String connectionString ="jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)}; DBQ=C:\\test\\TestEJFolder\\BWC_Ejournal.mdb;"; Driver
String connectionString ="jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)}; DBQ=C:\\test\\TestEJFolder\\BWC_Ejournal.mdb;";
DriverManager.getConnection(connectionString, "", "");
Connection conn = DriverManager.getConnection(connectionString, "", "");
Connection conn1 = DriverManager.getConnection(connectionString, "", "");
Connection conn2 = DriverManager.getConnection(connectionString, "", "");
String sql = "SELECT * FROM Events";
String dt = "SELECT TOP 1 [Date] FROM Events";
String count = "SELECT COUNT(ID) FROM Events";
Statement cmd = conn.createStatement();
Statement cmd1 = conn1.createStatement();
Statement cmd2 = conn2.createStatement();
cmd.execute(sql);
cmd1.execute(dt);
cmd2.execute(count);
ResultSet rc = cmd2.execute(count);
int r_count = cmd2.execute(count);
需要帮助来修复此问题。错误代码太多。开始阅读文章 试着这样做:
ResultSet rc = cmd2.execute(count);
int r_count = 0;
while (rc.next()) {
r_count = rc.getInt(1);
}
您没有关闭任何JDBC资源,这只会带来灾难
您应该将连接信息外部化
我会将您的更多内容封装到小型、独立的方法中,而不是以这种方式将多个语句混在一起
您应该考虑一个定义良好、基于接口的持久层
将这些SQL查询设为私有静态最终字符串。他们不必是本地人
我建议你试试这样的东西。从一个界面开始:
package persistence;
import java.util.List;
import java.util.Map;
/**
* EventDao
* @author Michael
* @link http://stackoverflow.com/questions/5016730/creating-a-dsn-less-connection-for-ms-access-within-java
* @since 6/25/13 5:19 AM
*/
public interface EventDao {
List<Map<String, Object>> findAllEvents();
}
然后编写一个实现:
package persistence;
import java.sql.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* EventDaoImpl
* @author Michael
* @link http://stackoverflow.com/questions/17213307/execute-access-query-in-resultset-java/17213356?noredirect=1#comment25072519_17213356
* @since 6/25/13 5:15 AM
*/
public class EventDaoImpl implements EventDao {
private static final String DEFAULT_URL = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)}; DBQ=C:\\test\\TestEJFolder\\BWC_Ejournal.mdb;";
private static final String SQL_FIND_ALL_EVENTS = "SELECT * FROM Events";
private Connection connection;
public EventDaoImpl(Connection connection) {
this.connection = connection;
}
@Override
public List<Map<String, Object>> findAllEvents() {
List<Map<String, Object>> results = new ArrayList<Map<String, Object>>();
Statement st = null;
ResultSet rs = null;
try {
st = this.connection.createStatement();
rs = st.executeQuery(SQL_FIND_ALL_EVENTS);
results = map(rs);
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
} finally {
close(rs);
close(st);
}
return results;
}
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;
}
}
行上结果集rc=cmd2.executecount;抛出相同的错误类型不匹配:无法从布尔值转换为结果。请阅读教程并学习如何编写Java和JDBC。自从1995年Java问世以来,这个问题已经解决了一百万次。你不是第一个。我的建议是一次一个问题。你有三种方法。那是错误的。一种方法应该做好一件事。使用其中一个查询,并使其在一个方法中工作。然后做其他的。