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对数据库的操作无非就是增删改查，其中数查询操作最为复杂，所以将查询单独讲解，我这里用的Mysql数据库
1.查询结果以list返回
2.查询结果以jsonArray返回
3.查询总记录条数
先看一下相关的配置信息
public static final String USER_NAME = "root"; public static final String PWD = "123456789"; public static final String DRIVER = "com.mysql.jdbc.Driver"; public static final String URL = "jdbc:mysql://localhost:3306/web_demon"; /** 分页查询默认每页记录条数 */ public static final int PAGE_SIZE_DEFAULT = 10;
获取数据库连接对象
/**
* 获取数据库连接
* @return 数据库连接对象
*/
public Connection getConnection(Connection conn) {
if(conn == null){
try {
Class.forName(Config.DRIVER);
conn = DriverManager.getConnection(Config.URL, Config.USER_NAME, Config.PWD);
} catch (Exception e) {
e.printStackTrace();
}
}
return conn;
}封装增删改操作
/**
* 新增，删除，插入操作
* @param sql 执行的sql语句
* 例如：新增语句 "insert into user (name,sex) values (?,?)";
* 删除语句 "delete from user where id=?";
* 修改语句 "update user set name=?,sex=? where id=? and sex=?";
* @param values 对应的参数值
* @return 影响条数，-1为异常
*/
private int execute(String sql,Object... values){
Connection conn = null;
PreparedStatement pStmt = null;
try {
conn = this.getConnection(conn);
pStmt = conn.prepareStatement(sql);
//设置参数
if(pStmt != null && values != null && values.length > 0){
for (int i = 0; i < values.length; i++) {
pStmt.setObject(i+1, values[i]);
}
}
int i =pStmt.executeUpdate();
return i;
} catch (Exception e) {
e.printStackTrace();
} finally {
if (conn != null) {
this.closeConnection(conn);
}
}
return -1;
}调用方法
//新增
public static void insert(){
String sql = "insert into user (name,sex) values (?,?)";
Object[] values = new Object[]{"李四",0};
int res = baseImp.execute(sql, values);
System.out.println("insert res="+res);
}
//删除
public static void delete(){
String sql = "delete from user where id=?";
Object[] values = new Object[]{2};
int res = baseImp.execute(sql, values);
System.out.println("delete res="+res);
}
//更新
public static void update(){
String sql = "update user set name=?,sex=? where id=? and sex=?";
Object[] values = new Object[]{"张三",1,1,0};
int res = baseImp.execute(sql, values);
System.out.println("update res="+res);
}/**
* 查询结果以list返回
* @param pageIndex 页数
* @param pageSize 每页记录条数
* @param attachTableName 在结果集中是否给key值附加表名，例如：user.id,与id
* @param sql 查询语句 例如："select u.id,u.name,u.sex,u.depart_id AS departId,d.* from user u,depart d where u.depart_id=d.id"
* @param values
* @throws SQLException
*/
private List<Map<String, Object>> queryList(int pageIndex,int pageSize,boolean attachTableName,String sql,Object... values) throws SQLException{
Connection conn = null;
PreparedStatement pStmt = null;
List<Map<String, Object>> dataList = null;
//校验参数
if(pageIndex <= 0){
pageIndex = 1;
}
if(pageSize <= 0){
pageSize = Config.PAGE_SIZE_DEFAULT;
}
conn = this.getConnection(conn);
pStmt = conn.prepareStatement(sql);
//设置参数
if(pStmt != null && values != null && values.length > 0){
for (int i = 0; i < values.length; i++) {
pStmt.setObject(i+1, values[i]);
}
}
//设置最大查询到第几条记录
pStmt.setMaxRows(pageIndex*pageSize);
ResultSet rs = pStmt.executeQuery();
//游标移动到要输出的第一条记录
rs.relative((pageIndex-1)*pageSize);
if(rs != null){
try {
dataList = new ArrayList<Map<String,Object>>();
ResultSetMetaData md = rs.getMetaData(); //得到结果集(rs)的结构信息，比如字段数、字段名等
//遍历结果集
while(rs.next()){
Map<String, Object> map = new LinkedHashMap();
for (int i = 1; i <= md.getColumnCount(); i++) {
map.put(attachTableName?(formatTableName(md.getTableName(i))+"."+md.getColumnLabel(i)):(md.getColumnLabel(i)), rs.getObject(i));
}
dataList.add(map);
}
}finally{
if(rs != null){
rs.close();
}
if(pStmt != null){
pStmt.close();
}
if (conn != null) {
this.closeConnection(conn);
}
}
}
return dataList;
}调用list查询
public static void queryList(){
String sql = "select u.*,d.* from user u,depart d where u.depart_id=d.id";
try {
List<Map<String, Object>> dataList = baseImp.queryForListAttachTableName(2,2,sql, null);
// List<Map<String, Object>> dataList = baseImp.queryForList(2,2,sql, null);
for (Map<String, Object> map : dataList) {
for (String key : map.keySet()) {
System.out.print(key+"="+map.get(key)+" ");
}
System.out.println();
}
} catch (SQLException e) {
e.printStackTrace();
}
}结果
/**
* 查询结果以ArrayList返回
* @param 在结果集中是否给key值附加表名，例如：user.id,与id
* @param sql 查询语句 例如："select u.id,u.name,u.sex,u.depart_id AS departId,d.* from user u,depart d where u.depart_id=d.id"
* @param values
* @throws SQLException
*/
private JSONArray queryJsonArray(int pageIndex,int pageSize,boolean attachTableName,String sql,Object... values) throws SQLException{
JSONArray jsonArray = null;
Connection conn = null;
PreparedStatement pStmt = null;
//校验参数
if(pageIndex <= 0){
pageIndex = 1;
}
if(pageSize <= 0){
pageSize = Config.PAGE_SIZE_DEFAULT;
}
conn = this.getConnection(conn);
pStmt = conn.prepareStatement(sql);
//设置参数
if(pStmt != null && values != null && values.length > 0){
for (int i = 0; i < values.length; i++) {
pStmt.setObject(i+1, values[i]);
}
}
//设置最大查询到第几条记录
pStmt.setMaxRows(pageIndex*pageSize);
ResultSet rs = pStmt.executeQuery();
//游标移动到要输出的第一条记录
rs.relative((pageIndex-1)*pageSize);
if(rs != null){
try {
jsonArray = new JSONArray();
ResultSetMetaData md = rs.getMetaData(); //得到结果集(rs)的结构信息，比如字段数、字段名等
//遍历结果集
while(rs.next()){
JSONObject jsonObject = new JSONObject();
for (int i = 1; i <= md.getColumnCount(); i++) {
jsonObject.put(attachTableName?(formatTableName(md.getTableName(i))+"."+md.getColumnLabel(i)):(md.getColumnLabel(i)), rs.getObject(i)+"");
}
jsonArray.add(jsonObject);
}
}finally{
if(rs != null){
rs.close();
}
if(pStmt != null){
pStmt.close();
}
if (conn != null) {
this.closeConnection(conn);
}
}
}
return jsonArray;
}public static void queryJsonArray(){
// String sql = "select * from user u";
String sql = "select u.*,d.* from user u,depart d where u.depart_id=d.id";
// String sql = "select u.id AS uid,u.name,u.sex,u.depart_id AS departId,d.name from user u,depart d where u.depart_id=d.id";
// String sql = "select u.id,u.name,u.sex,u.depart_id AS departId,d.* from user u,depart d where u.depart_id=d.id";
try {
JSONArray jsonArray = baseImp.queryForJsonArrayAttachTableName(2,2,sql, null);
// JSONArray jsonArray = baseImp.queryForJsonArray(sql, null);
System.out.println(jsonArray.toString());
for (int i = 0; i < jsonArray.size(); i++) {
JSONObject jsonObject = jsonArray.getJSONObject(i);
Iterator<?> iterator = jsonObject.keys();
Object key = null;
while (iterator.hasNext()) {
key = iterator.next();
System.out.print(key+" "+jsonObject.get(key)+" ");
}
System.out.println();
}
} catch (SQLException e) {
e.printStackTrace();
}
}结果
[{"user.id":"4","user.name":"王五","user.sex":"0","user.depart_id":"3","depart.id":"3","depart.name":"研发部","depart.desc":"这是研发部"},{"user.id":"5","user.name":"赵六","user.sex":"1","user.depart_id":"1","depart.id":"1","depart.name":"测试部","depart.desc":"这是测试部"}]
user.id 4 user.name 王五 user.sex 0 user.depart_id 3 depart.id 3 depart.name 研发部 depart.desc 这是研发部
user.id 5 user.name 赵六 user.sex 1 user.depart_id 1 depart.id 1 depart.name 测试部 depart.desc 这是测试部/**
* 查询记录条数
* @param sql 例如："select count(*) from user where xxx"
* @param values
* @throws SQLException
*/
public int queryCount(String sql,Object... values) throws SQLException{
int count = -1;
Connection conn = null;
PreparedStatement pStmt = null;
conn = this.getConnection(conn);
pStmt = conn.prepareStatement(sql);
//设置参数
if(pStmt != null && values != null && values.length > 0){
for (int i = 0; i < values.length; i++) {
pStmt.setObject(i+1, values[i]);
}
}
ResultSet rs = pStmt.executeQuery();
if(rs != null){
try {
while(rs.next()){
count = rs.getInt(1);
}
}finally{
if(rs != null){
rs.close();
}
if(pStmt != null){
pStmt.close();
}
if (conn != null) {
this.closeConnection(conn);
}
}
}
return count;
}调用查询总记录条数
public static void queryCount(){
String sql = "select count(*) from user u";
try {
System.out.println("count="+baseImp.queryCount(sql, null));
} catch (SQLException e) {
e.printStackTrace();
}
}结果
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