反射实战 使用反射,对JDBC进行强封装
作者:互联网
苦于学习了反射,却不知道在哪里使用?我这里给大伙整一个反射的小型实战
是使用反射封装JDBC的操作
因为查询需要支持复杂查询,所以没有办法去封装
剩下的CUD操作,都使用反射进行了强封装
如果你能看懂,并自己写下对用的代码,那么,你的反射就入门了!
好了,我们开始:
public class DBUtil {
static {
try {
Class.forName("com.mysql.cj.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
private static final String url="jdbc:mysql://localhost:3306/SQLStudy?serverTimezone=UTC";
private static final String name="admin";
private static final String password="123";
//受影响的行数
private int count=0;
private Connection conn = null;
private PreparedStatement stmt = null;
private ResultSet resultSet = null;
/**
* 获取数据库连接
* @return
*/
protected Connection getConnection() {
try {
conn = DriverManager.getConnection(url, name, password);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return conn;
}
/**
* 获取preparedStatement
* @param sql
* @param list
* @return
*/
protected PreparedStatement getStatement(String sql, List list) {
getConnection();
try {
stmt = conn.prepareStatement(sql);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
if (list!=null && list.size()>0) {
for (int i = 0; i < list.size(); i++) {
try {
stmt.setObject(i+1,list.get(i));
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
return stmt;
}
/**
* 依据新传入的对象,更新数据库中信息
* 使用反射,进行封装
* @param o
* @param c
* @param <T>
* @return
*/
protected <T> int update(Object o,Class<T> c) {
T obj=null;
if (o != null) {
obj=(T)o;
}
Field[] fields = c.getDeclaredFields();
StringBuilder sb = new StringBuilder();
sb.append("update ")
.append(c.getSimpleName().toLowerCase())
.append(" ")
.append("set ");
for (int i = 0; i < fields.length - 1; i++) {
sb.append(fields[i].getName().toLowerCase())
.append("=?,");
}
sb.append(fields[fields.length-1].getName())
.append("=? ");
sb.append("where id=?");
//需要根据 id,来修改对应的信息
String sql=sb.toString();
//System.out.println(sql);
//尝试设置值
Field[] declaredFields = c.getDeclaredFields();
List params = new ArrayList();
int len = declaredFields.length;
for (int i = 0; i < len; i++) {
fields[i].setAccessible(true);
try {
params.add(fields[i].get(obj));
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
//where id =? 设置 id
try {
params.add(fields[0].get(obj));
} catch (IllegalAccessException e) {
e.printStackTrace();
}
PreparedStatement stmt = getStatement(sql, params);
try {
count = stmt.executeUpdate();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return count;
}
/**
* 查询
* 因为还要支持复杂查询
* 所以没有办法通过反射,获取对应的实例
* @param sql
* @param params
* @return
*/
protected ResultSet query(String sql,List params) {
PreparedStatement stmt = getStatement(sql, params);
ResultSet res = null;
try {
res= stmt.executeQuery();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return res;
}
/**
* 使用反射,向数据库中,添加信息
* @param o
* @param c
* @param <T>
* @return
*/
protected <T> boolean insert(Object o,Class<T> c) {
T obj = null;
if (o!=null) {
obj = (T) o;
}
StringBuilder sb = new StringBuilder();
sb.append("insert into ")
.append(c.getSimpleName().toLowerCase())
.append(" ")
.append("values(");
Field[] fields = c.getDeclaredFields();
int len = fields.length;
for (int i = 0; i <len-1; i++) {
sb.append("?,");
}
sb.append("?)");
//获得 sql 语句
String sql=sb.toString();
//System.out.println(sql);
//获取所有参数
List params = new ArrayList();
for (int i = 0; i < len; i++) {
fields[i].setAccessible(true);
Object tmp=null;
try {
tmp = fields[i].get(obj);
} catch (IllegalAccessException e) {
e.printStackTrace();
}
params.add(tmp);
}
PreparedStatement stmt = getStatement(sql, params);
boolean res=false;
try {
res = stmt.execute();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return res;
}
/**
* 根据主键进行删除
* @param id
*/
protected<T> boolean delete(int id,Class<T>c) {
StringBuilder sb = new StringBuilder();
sb.append("delete from ")
.append(c.getSimpleName())
.append(" ")
.append("where id =?");
String sql = sb.toString();
List params = new ArrayList();
params.add(id);
PreparedStatement stmt = getStatement(sql, params);
boolean res=false;
try {
res = stmt.execute();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return res;
}
/**
* 关闭全部连接
*/
protected void close() {
if (resultSet!=null) {
try {
resultSet.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (stmt!=null) {
try {
stmt.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (conn!=null) {
try {
conn.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
使用的时候,需要Dao层的实现类,继承这个工具类,然后在Dao层实现类中,去使用封装的方法。
标签:反射,JDBC,封装,throwables,stmt,try,sql,catch,append 来源: https://blog.csdn.net/weixin_44062380/article/details/116522011