有了这个类 ，基本后台的所有逻辑操作都能实现，后端雏形就算搭建出来了
说说写这个类遇到的坑
1。Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 6, Size: 6
ResultSetMetaData中的getColumnCount()方法是从1开始的
代码如下：
resultSet = DbHelper.getStatement().executeQuery(sql);
ResultSetMetaData data = resultSet.getMetaData();
int columnsCount = data.getColumnCount();
for (int i = 1; i <= columnsCount; i++) {
String s = data.getColumnName(i);
list.add(s);
}
2。这些代码都实现了所需要的功能，但是没有优化
package com.lp.DAO;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import com.lp.bean.city;
import com.lp.bean.goods;
import com.sun.org.apache.bcel.internal.generic.GETSTATIC;
/**
* 2015.7.20 利用java反射机制实现万能DAO 即使bean层的实体类字段改变 也能实现增删查改
*
* @author liupeng
*/
public class DaoPro {
// 由数据库名称得到数据库中的所有列
public List<String> getColumns(String tableName) {
Connection connection = DbHelper.getCon();
Statement statement = DbHelper.getStatement();
ResultSet resultSet = null;
List<String> list = new ArrayList<String>();
try {
String sql = "select * from " + tableName + " where 1=2";
resultSet = DbHelper.getStatement().executeQuery(sql);
ResultSetMetaData data = resultSet.getMetaData();
int columnsCount = data.getColumnCount();
for (int i = 1; i <= columnsCount; i++) {
String s = data.getColumnName(i);
list.add(s);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
DbHelper.cloRes(connection, statement, resultSet);
}
return list;
}
// 得到数据库中的所有数据
public List getList(Class cl) {
int i = 0;
List objs = new ArrayList();
Connection connection = DbHelper.getCon();
Statement statement = DbHelper.getStatement();
ResultSet resultSet = null;
Field[] fields = cl.getDeclaredFields();
List<String> columnsName = getColumns(cl.getSimpleName());
String sql = "select * from " + cl.getSimpleName();
try {
System.out.println(sql);
resultSet = statement.executeQuery(sql);
System.out.println(i++);
while (resultSet.next()) {
System.out.println(i++);
Object obj = cl.newInstance();
for (String str : columnsName) {
for (Field ff : fields) {
if (str.equals(ff.getName())) {
ff.setAccessible(true);
ff.set(obj, resultSet.getObject(ff.getName()));
break;
}
}
}
objs.add(obj);
}
} catch (SQLException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
}
return objs;
}
// 添加数据返回主键的方法
public int addData(Object object) {
int id = 0;
Connection connection = DbHelper.getCon();
ResultSet resultSet = null;
PreparedStatement preparedStatement = null;
String tableName = object.getClass().getSimpleName();
Field[] fields = object.getClass().getDeclaredFields();
List<String> allColumns = getColumns(tableName);
StringBuffer buffer = new StringBuffer();
StringBuffer buffer1 = new StringBuffer();
buffer.append("insert into ");
buffer.append(tableName);
buffer.append(" (");
for (int i = 1; i < allColumns.size(); i++) {
buffer.append(allColumns.get(i));
buffer1.append("?");
if (i != allColumns.size() - 1) {
buffer.append(",");
buffer1.append(",");
}
}
buffer.append(") values (");
buffer.append(buffer1);
buffer.append(")");
// System.out.println(buffer.toString());
try {
preparedStatement = connection.prepareStatement(buffer.toString());
for (int i = 1; i < allColumns.size(); i++) {
for (int j = 0; j < fields.length; j++) {
if ((fields[j].getName()).equals(allColumns.get(i))) {
fields[j].setAccessible(true);
if (fields[j].get(object) == null) {
preparedStatement.setObject(i, "此字段无填充");
} else {
preparedStatement.setObject(i,
fields[j].get(object));
}
break;
}
}
}
int a = preparedStatement.executeUpdate();
if (a > 0) {
resultSet = preparedStatement.getGeneratedKeys();
if (resultSet.next()) {
id = resultSet.getInt(1);
}
}
} catch (SQLException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} finally {
DbHelper.cloRes(connection, preparedStatement, resultSet);
}
return id;
}
// 根据实体类实现一个或者多个条件查询
public List getByBean(Object object) {
List some = new ArrayList();
Connection connection = DbHelper.getCon();
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
try {
// 得到实体类不为空的属性和属性值
List<String> listVal = new ArrayList<String>();
List<String> listField = new ArrayList<String>();
Field[] fields = object.getClass().getDeclaredFields();
for (int i = 0; i < fields.length; i++) {
fields[i].setAccessible(true);
// 把id字段除去，知道id就不用查了
if (fields[i].get(object) != null
&& !(fields[i].get(object) instanceof Integer)) {
listVal.add((String) fields[i].get(object));
listField.add(fields[i].getName());
}
}
// 拼接sql语句
StringBuffer buffer = new StringBuffer();
buffer.append("select ");
buffer.append("*");
buffer.append(" from ");
buffer.append(object.getClass().getSimpleName());
buffer.append(" where ");
for (int i = 0; i < listField.size(); i++) {
buffer.append(listField.get(i));
buffer.append("=");
buffer.append("‘" + listVal.get(i) + "‘");
if (i != listField.size() - 1) {
buffer.append(" and ");
}
}
System.out.println(buffer.toString());
// 执行查询
preparedStatement = connection.prepareStatement(buffer.toString());
resultSet = preparedStatement.executeQuery();
int count = resultSet.getMetaData().getColumnCount();
while (resultSet.next()) {
Object ob = object.getClass().newInstance();
//获取不含id的列
List<String> list = getColumns(object.getClass()
.getSimpleName());
list.add("id");
Field[] fields2 = object.getClass().getDeclaredFields();
for (int j = 0; j < fields2.length; j++) {
fields2[j].setAccessible(true);
for (int i = 1; i <= list.size()-1; i++) {
if (list.get(i).equals(fields2[j].getName())) {
fields2[j].set(ob, resultSet.getObject(list.get(i)));
}
}
}
some.add(ob);
}
} catch (SQLException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} finally {
DbHelper.cloRes(connection, preparedStatement, resultSet);
}
return some;
}
// 更新数据，由实体类封装的id，得到主键，实现更新
public boolean updateBean(Object object) {
int id = 0;
int a = 0;
Connection connection = DbHelper.getCon();
Statement statement = null;
ResultSet resultSet = null;
Field[] fields = object.getClass().getDeclaredFields();
// 得到id的值，确定要更新那一条数据
try {
for (int i = 0; i < fields.length; i++) {
fields[i].setAccessible(true);
if (fields[i].getName().equals("id")) {
if ((Integer) fields[i].get(object) != 0) {
id = (Integer) fields[i].get(object);
} else {
return false;
}
}
}
// 拼接 sql 语句
StringBuffer buffer = new StringBuffer();
buffer.append("update ");
buffer.append(object.getClass().getSimpleName());
buffer.append(" set ");
List<String> list = getColumns(object.getClass().getSimpleName());
list.remove("id");
for (int i = 0; i < list.size(); i++) {
for (int j = 0; j < fields.length; j++) {
if (fields[j].getName().equals(list.get(i))) {
if (fields[j].get(object) != null) {
buffer.append(list.get(i));
buffer.append("=");
buffer.append("‘" + fields[j].get(object) + "‘,");
}
}
}
}
buffer.delete(buffer.length() - 1, buffer.length());
buffer.append(" where id=");
buffer.append(id);
System.out.println(buffer.toString());
statement = connection.createStatement();
a = statement.executeUpdate(buffer.toString());
System.out.println(a);
} catch (Exception e) {
e.printStackTrace();
} finally {
DbHelper.cloRes(connection, statement, resultSet);
}
if (a > 0) {
return true;
}
return false;
}
public static void main(String[] args) {
goods c = new goods();
c.setGoodDetail("我的更改");
goods good = (goods) new DaoPro().getByBean(c).get(0);
System.out.println(good.getId());
}
}
时间： 2024-10-15 10:15:22