JDBC中CommonDao的設計，策略模式和反射
阿新 • • 發佈：2018-12-09
普通方法：
CommonDao.java
public class CommonDao { /** * 此方法是公共方法，專門獲取資料庫連線 * @return */ public static Connection getConnection(){ Connection con=null; try { Class.forName("com.mysql.jdbc.Driver"); con=DriverManager.getConnection("jdbc:mysql://localhost:3306/testdb","root","0118"); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return con; } /** * 此方法是公共方法，專門用來關閉資料庫資源 * @param rs * @param pstmt * @param con */ public static void closeAll(ResultSet rs,PreparedStatement pstmt,Connection con){ try { if(rs!=null){ rs.close(); }if(pstmt!=null){ pstmt.close(); }if(con!=null){ con.close(); } } catch (Exception e) { // TODO: handle exception } }
UserDao.java
public class UserDao implements UserDao{ @Override public User login(String userName, String userPassword) throws SQLException { // TODO Auto-generated method stub User user = null; Connection con = CommonDao.getConnection(); String sql="select id from t_user where username=? and password=?"; PreparedStatement pstmt=con.prepareStatement(sql); pstmt.setString(1, userName); pstmt.setString(2,userPassword); ResultSet rs = pstmt.executeQuery(); if(rs.next()){ user = new User(); user.setUserId(rs.getInt("user_id")); user.setUserName(rs.getString("user_name")); user.setUserPassword(rs.getString("user_password")); } CommonDao.closeAll(rs, pstmt, con); return user; } @Override public int addUser(User user) throws SQLException { // TODO Auto-generated method stub int rowAffect = 0; Connection con = CommonDao.getConnection(); String sql="insert into t_user(username,password) values(?,?)"; PreparedStatement pstmt = con.prepareStatement(sql); pstmt.setString(1, user.getUserName()); pstmt.setString(2, user.getUserPassword()); rowAffect = pstmt.executeUpdate(sql); CommonDao.closeAll(null, pstmt, con); return rowAffect ; }
優化：策略模式
UserDao中存在大量的重複程式碼，比如資料庫的連線與關閉，PrepareStatement的資料填充操作，不同的是sql語句和對ResultSet結果集的操作，所以可以使用策略模式對程式碼進行優化
RowMapper.java
public interface RowMapper<T> {
public T mapRow(ResultSet rs) throws SQLException;
}CommonDao.java
public class CommonDao { /** * 此方法是公共方法，專門獲取資料庫連線 * @return */ public static Connection getConnection(){ Connection con=null; try { Class.forName("com.mysql.jdbc.Driver"); con=DriverManager.getConnection("jdbc:mysql://localhost:3306/testdb","root","0118"); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return con; } /** * 此方法是公共方法，專門用來關閉資料庫資源 * @param rs * @param pstmt * @param con */ public static void closeAll(ResultSet rs,PreparedStatement pstmt,Connection con){ try { if(rs!=null){ rs.close(); }if(pstmt!=null){ pstmt.close(); }if(con!=null){ con.close(); } } catch (Exception e) { // TODO: handle exception } } /** * 通用更新 * @param sql DML語句 * @param params 引數 * @return * @throws SQLException */ public static int executeUpdate(String sql,Object...params) throws SQLException{ int rowAffect = 0; Connection con = getConnection(); PreparedStatement pstmt = con.prepareStatement(sql); if(params!=null){ for(int i=0;i<params.length;i++){ pstmt.setObject(i+1, params[i]); } } rowAffect = pstmt.executeUpdate(); closeAll(null, pstmt, con); return rowAffect; } /** * 通用查詢 * @param sql * @param params * @param rm * @return * @throws SQLException */ public static <T> List<T> executeQuery(String sql,RowMapper<T> rm,Object...params) throws SQLException{ List<T> list = new ArrayList<T>(); Connection con = getConnection(); PreparedStatement pstmt = con.prepareStatement(sql); if(params!=null){ for(int i=0;i<params.length;i++){ pstmt.setObject(i+1, params[i]); } } ResultSet rs = pstmt.executeQuery(); while(rs.next()){ T mapRow = rm.mapRow(rs); list.add(mapRow); } closeAll(rs, pstmt, con); return list; } }
UserDao.java
public class UserMysql implements UserDao{
@Override
public User login(String userName, String userPassword) throws SQLException {
// TODO Auto-generated method stub
User user = null;
String sql="select user_id from t_user where user_name=? and user_password=?";
RowMapper<User> rm = new RowMapper<User>() {
@Override
public User mapRow(ResultSet rs) throws SQLException {
User user = new User();
user.setUserId(rs.getInt("user_id"));
user.setUserName(rs.getString("user_name"));
user.setUserPassword(rs.getString("user_password"));
return user;
}
};
Object[] params = {userName,userPassword};
user = CommonDao.executeQuery(sql, rm, params).get(0);
return user;
}
@Override
public int addUser(User user) throws SQLException {
// TODO Auto-generated method stub
int rowAffect = 0;
String sql="insert into t_user(user_name,user_password) values(?,?)";
rowAffect = CommonDao.executeUpdate(sql, user.getUserName(),user.getUserPassword());
return rowAffect;
}
}優化：反射1.0
對於通用查詢，雖然策略模式可以節省很多工作，但是每次都要去寫不同實現，還是比較費事，通過觀察可以發現，從資料庫中取出的結果集是和User實體類一 一對應的，所以可以使用反射對程式碼再一次進行優化
CommonDao.java
public class CommonDao {
/**
* 此方法是公共方法，專門獲取資料庫連線
* @return
*/
public static Connection getConnection(){
Connection con=null;
try {
Class.forName("com.mysql.jdbc.Driver");
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/testdb","root","0118");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return con;
}
/**
* 此方法是公共方法，專門用來關閉資料庫資源
* @param rs
* @param pstmt
* @param con
*/
public static void closeAll(ResultSet rs,PreparedStatement pstmt,Connection con){
try {
if(rs!=null){
rs.close();
}if(pstmt!=null){
pstmt.close();
}if(con!=null){
con.close();
}
} catch (Exception e) {
// TODO: handle exception
}
}
/**
* 通用更新
* @param sql DML語句
* @param params 引數
* @return
* @throws SQLException
*/
public static int executeUpdate(String sql,Object...params) throws SQLException{
int rowAffect = 0;
Connection con = getConnection();
PreparedStatement pstmt = con.prepareStatement(sql);
if(params!=null){
for(int i=0;i<params.length;i++){
pstmt.setObject(i+1, params[i]);
}
}
rowAffect = pstmt.executeUpdate();
closeAll(null, pstmt, con);
return rowAffect;
}
/**
* 通用DQL,，反射版本
* @param sql 只能是DQL語句
* @param params 佔位符的值
* @param class 實體物件，物件儲存的是資料庫的資料
* @return
* @throws SQLException
* @throws IllegalAccessException
* @throws InstantiationException
*/
public static <T> List<T> executeQuery(String sql,Class<T> clazz,Object...params) throws Exception{
List<T> list = new ArrayList<T>();
Connection con = getConnection();
PreparedStatement pstmt = con.prepareStatement(sql);
if(params!=null){
for(int i=0;i<params.length;i++){
pstmt.setObject(i+1, params[i]);
}
}
ResultSet rs = pstmt.executeQuery();
//獲取結果集的元資料
ResultSetMetaData rsmd = rs.getMetaData();
//從結果的元資料中獲取結果集的元資料，元資料就是結果集的列資訊
List<String> columnNames = new ArrayList<String>();//儲存結果的列頭的名字
for(int i=0;i<rsmd.getColumnCount();i++){
columnNames.add(rsmd.getColumnLabel(i+1));
}
while(rs.next()){
//例項化T型別的實體物件
T t = clazz.newInstance();
//用反射呼叫t中的set方法
for(String columnName:columnNames){
//類似於setId setUserName setUserPassword
String setterName = "set"+columnName.substring(0,1).toUpperCase()+columnName.substring(1);
Method[] methods = clazz.getDeclaredMethods();
for(Method m:methods){
m.invoke(t, value);
}
}
}
list.add(t);
}
closeAll(rs, pstmt, con);
return list;
}
}UserDao.java
public class UserDaoImpl implements UserDao{
@Override
public int login(String userName, String userPassword) throws Exception {
// TODO Auto-generated method stub
User user = null;
String sql="select user_id as userId from t_user where username=? and password=?";
Object[] params = new Object[] {userName,userPassword};
List<User> list = CommonDao.executeQuery(sql, User.class, params);
user = list.get(0);
return user;
}
@Override
public int addUser(User user) throws SQLException {
// TODO Auto-generated method stub
int rowAffect = 0;
String sql="insert into t_user(user_name,user_password) values(?,?)";
rowAffect = CommonDao.executeUpdate(sql,user.getUserName(),user.getUserPassword());
return rowAffect;
}
這樣一來，UserDao中方法的程式碼又少了很多，但是上面反射有一個問題就是，每次獲取方法名時都要將columnNames遍歷一遍，這樣的話對於資源的消耗會比較大，所以。。。。
優化：反射2.0
Class中還有一個方法就是 Method (String name, Class<?>... parameterTypes)，可以直接通過方法名獲取類的方法，那麼問題來了，方法還需要查詢方法引數的類型別，這個。。。
解決：ResultSetMetaData這個物件有兩個方法 int (int column) 和 String (int column)
方法
檢視colType和colTypeName
註釋大概意思是colType是java.sql.Type中的型別，colTypeName是資料來源的型別名稱
如果想讓程式有更好的相容性，那麼colTypeName肯定是不行的，因為不同的資料庫欄位的型別名稱也不同，但是java.sql.Types就不一樣了，這是jdk定義的型別，屬於java的十三種規範之一JDBC，不同的資料庫廠商都會按照這個標準去做資料庫驅動
java.sql.Types的原始碼
/*
* Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*/
package java.sql;
/**
* <P>The class that defines the constants that are used to identify generic
* SQL types, called JDBC types.
* <p>
* This class is never instantiated.
*/
public class Types {
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>BIT</code>.
*/
public final static int BIT = -7;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>TINYINT</code>.
*/
public final static int TINYINT = -6;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>SMALLINT</code>.
*/
public final static int SMALLINT = 5;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>INTEGER</code>.
*/
public final static int INTEGER = 4;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>BIGINT</code>.
*/
public final static int BIGINT = -5;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>FLOAT</code>.
*/
public final static int FLOAT = 6;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>REAL</code>.
*/
public final static int REAL = 7;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>DOUBLE</code>.
*/
public final static int DOUBLE = 8;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>NUMERIC</code>.
*/
public final static int NUMERIC = 2;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>DECIMAL</code>.
*/
public final static int DECIMAL = 3;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>CHAR</code>.
*/
public final static int CHAR = 1;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>VARCHAR</code>.
*/
public final static int VARCHAR = 12;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>LONGVARCHAR</code>.
*/
public final static int LONGVARCHAR = -1;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>DATE</code>.
*/
public final static int DATE = 91;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>TIME</code>.
*/
public final static int TIME = 92;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>TIMESTAMP</code>.
*/
public final static int TIMESTAMP = 93;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>BINARY</code>.
*/
public final static int BINARY = -2;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>VARBINARY</code>.
*/
public final static int VARBINARY = -3;
/**
* <P>The constant in the Java programming language, sometimes referred
* to as a type code, that identifies the generic SQL type
* <code>LONGVARBINARY</code>.
*/
public final static int LONGVARBINARY = -4;
/**
* <P>The constant in the Java programming language
* that identifies the generic SQL value
* <code>NULL</code>.
*/
public final static int NULL = 0;
/**
* The constant in the Java programming language that indicates
* that the SQL type is database-specific and
* gets mapped to a Java object that can be accessed via
* the methods <code>getObject</code> and <code>setObject</code>.
*/
public final static int OTHER = 1111;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* <code>JAVA_OBJECT</code>.
* @since 1.2
*/
public final static int JAVA_OBJECT = 2000;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* <code>DISTINCT</code>.
* @since 1.2
*/
public final static int DISTINCT = 2001;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* <code>STRUCT</code>.
* @since 1.2
*/
public final static int STRUCT = 2002;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* <code>ARRAY</code>.
* @since 1.2
*/
public final static int ARRAY = 2003;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* <code>BLOB</code>.
* @since 1.2
*/
public final static int BLOB = 2004;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* <code>CLOB</code>.
* @since 1.2
*/
public final static int CLOB = 2005;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* <code>REF</code>.
* @since 1.2
*/
public final static int REF = 2006;
/**
* The constant in the Java programming language, somtimes referred to
* as a type code, that identifies the generic SQL type <code>DATALINK</code>.
*
* @since 1.4
*/
public final static int DATALINK = 70;
/**
* The constant in the Java programming language, somtimes referred to
* as a type code, that identifies the generic SQL type <code>BOOLEAN</code>.
*
* @since 1.4
*/
public final static int BOOLEAN = 16;
//------------------------- JDBC 4.0 -----------------------------------
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type <code>ROWID</code>
*
* @since 1.6
*
*/
public final static int ROWID = -8;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type <code>NCHAR</code>
*
* @since 1.6
*/
public static final int NCHAR = -15;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type <code>NVARCHAR</code>.
*
* @since 1.6
*/
public static final int NVARCHAR = -9;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type <code>LONGNVARCHAR</code>.
*
* @since 1.6
*/
public static final int LONGNVARCHAR = -16;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type <code>NCLOB</code>.
*
* @since 1.6
*/
public static final int NCLOB = 2011;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type <code>XML</code>.
*
* @since 1.6
*/
public static final int SQLXML = 2009;
//--------------------------JDBC 4.2 -----------------------------
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type {@code REF CURSOR}.
*
* @since 1.8
*/
public static final int REF_CURSOR = 2012;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* {@code TIME WITH TIMEZONE}.
*
* @since 1.8
*/
public static final int TIME_WITH_TIMEZONE = 2013;
/**
* The constant in the Java programming language, sometimes referred to
* as a type code, that identifies the generic SQL type
* {@code TIMESTAMP WITH TIMEZONE}.
*
* @since 1.8
*/
public static final int TIMESTAMP_WITH_TIMEZONE = 2014;
// Prevent instantiation
private Types() {}
}
其中不同的數字對應了不同的資料型別
如果還不太清楚的話可以參照 Java資料型別和MySql資料型別對應
那麼
CommonDao.java
/**
* 通用查詢
* @param sql
* @param clazz
* @param params
* @return
* @throws Exception
*/
public static <T> List<T> executeQuery(String sql,Class<T> clazz,Object...params)throws Exception{
Connection con = getConnection();
PreparedStatement pstmt = con.prepareStatement(sql);
List<T> list = new ArrayList<T>();
if(params!=null){
for(int i=0;i<params.length;i++){
pstmt.setObject(i+1, params[i]);
}
}
ResultSet rs = pstmt.executeQuery();
//獲取結果集元資料
ResultSetMetaData metaData = rs.getMetaData();
while(rs.next()){
T t = clazz.newInstance();
for(int i=1;i<=metaData.getColumnCount();i++){
String columnName = metaData.getColumnLabel(i);
String methodName = "set"+columnName.substring(0, 1).toUpperCase()+columnName.substring(1);
Class<?> paramType = null;
if(metaData.getColumnType(i)==4){
paramType=Integer.class;
}else if(metaData.getColumnType(i)==12){
paramType=String.class;
}
Method method = clazz.getDeclaredMethod(methodName, new Class[]{paramType});
method.invoke(t, rs.getObject(columnName));
}
list.add(t);
}
return list;
} 在這個Demo中我只使用了兩種資料型別，所以並沒有寫過多的程式碼，當然，也可以根據自己的需要，將型別的判斷寫成一個方法，去進行型別的選擇