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java 使用策略模式操作JDBC数据库
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1：构造一个操作数据库的工具类，可以获得连接和释放连接
public class DBUtil {
private static Connection conn = null;
static { //静态初始块
try {
Class.forName("com.MySQL.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "064319"); //初始化获取连接
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
}
/**
* 释放连接
* @param rs
* @param psmt
* @param conn
* @throws SQLException
*/
public static void closeAll(ResultSet rs, PreparedStatement psmt, Connection conn) throws SQLException {
if(rs != null) {
rs.close();
}
if(psmt != null) {
psmt.close();
}
if(conn != null) {
conn.close();
}
}
/**
* 获取连接
* @return
*/
public static Connection getConnection() {
return conn;
}
/**
* 根据表的名字来获得表的列信息
* @param tableName
*/
public static void getTableColumnInfoByTableName(String tableName) {
Connection conn = getConnection();
ResultSet rs = null;
PreparedStatement psmt = null;
String sql = "select * from " + tableName;
try {
psmt = conn.prepareStatement(sql);
rs = psmt.executeQuery();
ResultSetMetaData resultSetMetaData = rs.getMetaData();
for(int i = 1; i<= resultSetMetaData.getColumnCount(); i++) {
System.out.println(resultSetMetaData.getColumnName(i));
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
closeAll(rs, psmt, conn);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/**
* 根据表的名字来获得表的信息
* @param tableName
*/
public static void getTableInfoByTableName(String tableName) {
Connection conn = getConnection();
PreparedStatement psmt = null;
ResultSet rs = null;
String sql = "select * from " + tableName;
try {
psmt = conn.prepareStatement(sql);
rs = psmt.executeQuery();
while(rs.next()) {
ResultSetMetaData resultSetMetaData = rs.getMetaData();
for(int i = 1; i<= resultSetMetaData.getColumnCount(); i++) {
if(i < resultSetMetaData.getColumnCount()) {
System.out.print(rs.getObject(resultSetMetaData.getColumnName(i)) + ", ");
} else {
System.out.print(rs.getObject(resultSetMetaData.getColumnName(i)));
}
}
System.out.println();
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
closeAll(rs, psmt, conn);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
2：构造一个操作数据库的BaseDao类
public class BaseDao {
/**
* 根据一些参数来保存相应的对象
* @param sql 要执行的sql语句
* @param params 为sql语句中相应的参数赋值
* @return
*/
protected boolean saveOrUpdate(String sql, Object[] params) {
Connection conn = null;
PreparedStatement psmt = null;
boolean flag = false;
conn = DBUtil.getConnection();
if(conn != null) {
try {
psmt = conn.prepareStatement(sql);
for(int i = 1; i <= params.length; i++) {
psmt.setObject(i, params[i-1]);
}
if(psmt.executeUpdate() > 0) {
flag = true;
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
DBUtil.closeAll(null, psmt, conn);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
return flag;
}
/**
* 根据一定的参数获得某个具体的对象
* @param sql 要执行的sql语句
* @param params 为sql语句中相应的参数赋值
* @return
*/
public Object queryForObject(String sql, Object[] params, RowMapForObject rowMapForObject) {
Connection conn = null;
PreparedStatement psmt = null;
conn = DBUtil.getConnection();
Object obj = null;
ResultSet rs = null;
if(conn != null) {
try {
psmt = conn.prepareStatement(sql);
if(params != null && params.length > 0) {
for(int i = 1; i <= params.length; i++) {
psmt.setObject(i, params[i - 1]);
}
}
rs = psmt.executeQuery();
obj = rowMapForObject.rowMapForObject(rs);
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
DBUtil.closeAll(null, psmt, conn);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
return obj;
}
/**
* 根据相应的参数获得查询的结果集
* @param sql
* @param params
* @return
*/
public List queryForList(String sql, Object[] params, RowMapForList rowMapForList) {
Connection conn = null;
PreparedStatement psmt = null;
conn = DBUtil.getConnection();
List list = null;
ResultSet rs = null;
if(conn != null) {
try {
psmt = conn.prepareStatement(sql);
if(params != null && params.length > 0) {
for(int i = 1; i <= params.length; i++) {
psmt.setObject(i, params[i - 1]);
}
}
rs = psmt.executeQuery(sql);
list = new ArrayList();
list = rowMapForList.rowMapForList(rs);
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
DBUtil.closeAll(null, psmt, conn);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
return list;
}
}
3：新建一个StudentDao类，该类继承自BaseDao，实现对Student的管理
public class StudentDao extends BaseDao {
/**
* 保存一个Student的信息
*/
public boolean saveStudent(Student student) {
String sql = "insert into t_student(name, age) values(?, ?)";
Object[] params = new Object[]{student.getName(), student.getAge()};
return super.saveOrUpdate(sql, params);
}
/**
* 根据id获得一个Student的信息
* @param id
* @return
*/
public Student getStudentById(long id) {
String sql = "select * from t_student where id=?";
Object[] params = new Object[]{id};
return (Student)super.queryForObject(sql, params, new RowMapForObject() {
public Object rowMapForObject(ResultSet rs) {
Student student = null;
try {
if(rs != null && rs.next()) {
student = new Student();
student.setAge(rs.getInt(Student.AGE));
student.setId(rs.getLong(Student.ID));
student.setName(rs.getString(Student.NAME));
}
} catch (SQLException e) {
e.printStackTrace();
}
return student;
}
});
}
/**
* 获得所有Student的信息
* @return
*/
public List getStudentAll() {
String sql = "select * from t_student";
List list = super.queryForList(sql, null, new RowMapForList() {
@Override
public List rowMapForList(ResultSet rs) {
List list = null;
try {
if(rs != null) {
list = new ArrayList();
while(rs.next()) {
Student student = new Student();
student.setId(rs.getLong("id"));
student.setAge(rs.getInt("age"));
student.setName(rs.getString("name"));
list.add(student);
}
}
} catch(SQLException e) {
e.printStackTrace();
}
return list;
}
});
return list;
}
}
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