JDBC中典型的五种查询方式

//第一种查询方式,返回一个ArrayList集合,集合里面的数据类型只能为Empinfo类类型

public ArrayList<Empinfo> select01(){

ArrayList<Empinfo> list = new ArrayList<Empinfo>();//定义一个类类型的集合

conn = DBHelper.getConnection();//获取数据库连接

String sql = "select * from empinfo";//查询语句

try{

stmt = conn.createStatement();//创建Statement对象

rs = stmt.executeQuery(sql);//执行sql语句

while(rs.next()){

Empinfo e = new Empinfo();//创建一个Empinfo类对象，将从数据库当中获取到的值赋给对应的成员变量

e.setUid(rs.getInt("uid"));//或者为e.setUid(rs.getInt(1));

e.setDid(rs.getInt(2));//2表示数据库表当中的第2列,即name列

e.setName(rs.getString(3));

e.setSex(rs.getString("sex"));

e.setSalary(rs.getString(5));

list.add(e);

}

// for(int i = 0; i < list.size(); i++){

// System.out.println(list.get(i));//打印出集合里面的数据,一般用在外部调用方法中

// }

return list;

}catch(Exception e){

e.printStackTrace();

return null;

}finally{

try{

if(rs!=null){

rs.close();

rs = null;

}

if(stmt!=null){

stmt.close();

stmt = null;

}

}catch(Exception e){

e.printStackTrace();

}

}

}//

//第二种查询方式,返回一个Vector集合,集合里面数据类型为Empinfo,带条件查询的单表查询

public Vector<Empinfo> select02(int did,String sex){

Vector<Empinfo> v = new Vector<Empinfo>();

conn = DBHelper.getConnection();

String sql = "select * from empinfo where did = ? and sex = ?";

try{

pstmt = conn.prepareStatement(sql);

pstmt.setInt(1, did);//设置第一个问号的值

pstmt.setString(2, sex);//设置第二个问号的值

rs = pstmt.executeQuery();

while(rs.next()){

Empinfo e = new Empinfo();//创建一个Empinfo类对象，将从数据库当中获取到的值赋给对应的成员变量

e.setUid(rs.getInt(1));//或者为e.setUid(rs.getInt(1));

e.setDid(rs.getInt(2));//2表示数据库表当中的第2列,即name列

e.setName(rs.getString(3));

e.setSex(rs.getString(4));

e.setSalary(rs.getString(5));

v.add(e);

}

for(int i = 0; i < v.size(); i++){

System.out.println(v.get(i));

}

return v;

}catch(Exception e){

e.printStackTrace();

return null;

}finally{

try{

if(rs!=null){

rs.close();

rs = null;

}

if(pstmt!=null){

pstmt.close();

pstmt = null;

}

}catch(Exception e){

e.printStackTrace();

}

}

}//

//第三种查询方式,返回一个Object类型,多表查询的结果

public Vector<Object> select03(String sql){

Vector<Object> v = new Vector<Object>();

conn = DBHelper.getConnection();

try{

stmt = conn.createStatement();

rs = stmt.executeQuery(sql);

while(rs.next()){

Empinfo e = new Empinfo();

Departinfo d = new Departinfo();

e.setUid(rs.getInt(1));

e.setName(rs.getString(3));

e.setDid(rs.getInt(2));

e.setSex(rs.getString(4));

e.setSalary(rs.getString(5));

d.setDid(rs.getInt(6));

d.setName(rs.getString(7));

v.add(e);

v.add(d);

}

for(int i = 0; i < v.size(); i++){

System.out.println(v.get(i));

}

return v;

}catch(Exception e){

e.printStackTrace();

return null;

}finally{

try{

if(rs!=null){

rs.close();

rs = null;

}

if(pstmt!=null){

pstmt.close();

pstmt = null;

}

}catch(Exception e){

e.printStackTrace();

}

}

}//

//第四种查询方式,返回一个二维集合Vector<Vector<String>>,相当于一个二维数组,可以取出每一条里面每一个字段的值

public Vector<Vector<String>> select04(int did){

Vector<Vector<String>> v = new Vector<Vector<String>>();

Vector<String> v1 = new Vector<String>();

conn = DBHelper.getConnection();

String sql = "SELECT e.uid,d.name,e.name,e.sex,e.salary FROM" +

" empinfo e,departinfo d WHERE e.did = d.did and d.did = ?";

try{

pstmt = conn.prepareStatement(sql);

pstmt.setInt(1,did);

rs = pstmt.executeQuery();

rsmd = rs.getMetaData();

for(int i = 0;i < rsmd.getColumnCount();i++){

v1.add(rsmd.getColumnName(i+1)); //取出列名

}

v.add(v1);
//将列名这一行加入到大集合当中

while(rs.next()){

Vector<String> v2 = new Vector<String>();

for(int i = 0;i < rsmd.getColumnCount();i++){

v2.add(rs.getString(i+1)); //取出每一列对应的值

}

v.add(v2);
//将每一行的值加入到大集合当中

}

for(int i = 0; i < v.size(); i++){

System.out.println(v.get(i));

}

return v;

}catch(Exception e){

e.printStackTrace();

return null;

}finally{

try{

if(rs!=null){

rs.close();

rs = null;

}

if(pstmt!=null){

pstmt.close();

pstmt = null;

}

}catch(Exception e){

e.printStackTrace();

}

}

}//

//第五种查询方式,模糊查询,返回一个集合ArrayList<ArrayList<String>>

public ArrayList<ArrayList<String>> select05(String[] s){

ArrayList<ArrayList<String>> list = new ArrayList<ArrayList<String>>();

ArrayList<String> list01 = new ArrayList<String>();

conn = DBHelper.getConnection();

String uid = s[0];

String did = s[1];

String name = s[2];

String sex = s[3];

String salary_min = s[4];

String salary_max = s[5];

if(uid.equals("")){

uid="%";

}

if(did.equals("")){

did="%";

}

if(name.equals("")){

name="%";

}

if(sex.equals("不限")){

sex="%";

}

if(salary_min.equals("")){

salary_min="0";

}

if(salary_max.equals("")){

salary_max="999999999";

}

String sql = "select * from empinfo e, departinfo d where e.uid like '"+uid+"' and " +

" e.did like '"+did+"' and e.name like '%"+name+"%' and sex like '"+sex+"'" +

"and e.salary>'"+salary_min+"' and e.salary<'"+salary_max+"' " +

" and e.did=d.did order by e.uid";

try{

pstmt = conn.prepareStatement(sql);

//pstmt.setInt(1,did);

rs = pstmt.executeQuery();

rsmd = rs.getMetaData();

for(int i = 0;i < rsmd.getColumnCount();i++){

list01.add(rsmd.getColumnName(i+1)); //取出列名

}

list.add(list01);
//将列名这一行加入到大集合当中

while(rs.next()){

ArrayList<String> v2 = new ArrayList<String>();

for(int i = 0;i < rsmd.getColumnCount();i++){

v2.add(rs.getString(i+1)); //取出每一列对应的值

}

list.add(v2);
//将每一行的值加入到大集合当中

}

for(int i = 0; i < list.size(); i++){

System.out.println(list.get(i));

}

return list;

}catch(Exception e){

e.printStackTrace();

return null;

}finally{

try{

if(rs!=null){

rs.close();

rs = null;

}

if(pstmt!=null){

pstmt.close();

pstmt = null;

}

}catch(Exception e){

e.printStackTrace();

}

}

}

public static void main(String[] args) {

Test02 t = new Test02();

t.select05(new String[]{"","","","不限","",""});

}