动态条件查询

根据用户给定的条件来决定执行什么样的查询

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
/**
 * 动态查询
 */
public class DynamicConditionQueryTest {
    public List<Users> queryUsers(Users users){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        List<Users> list = new ArrayList<>();
        try {
            connection = JDBCUtils.getConnection();
            //拼接查询sql语句
            String sql = this.generateSql(users);
            System.out.println(sql);
            preparedStatement = connection.prepareStatement(sql);
            resultSet=preparedStatement.executeQuery();
            while(resultSet.next()){
                users = new Users();
                users.setUsername(resultSet.getString("username"));
                users.setUserid(resultSet.getInt("userid"));
                users.setUserage(resultSet.getInt("userage"));
                list.add(users);
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            JDBCUtils.clossResource(resultSet,preparedStatement,connection);
        }
        return list;
    }
    /**
     * 生成动态条件查询sql语句
     */
    private String generateSql(Users users){
        StringBuffer stringBuffer = new StringBuffer("select * from users where 1=1 ");
        if(users.getUserid()>0){
            stringBuffer.append(" and userid=").append(users.getUserid());
        }
        if(users.getUsername()!=null&&users.getUsername().length()>0){
            stringBuffer.append(" and username='").append(users.getUsername()); //字符串类型注意处理
        }
        if(users.getUserage()>0){
            stringBuffer.append(" and userage=").append(users.getUserage());
        }
        return stringBuffer.toString();
    }
    public static void main(String[] args) {
        DynamicConditionQueryTest dynamicConditionQueryTest = new DynamicConditionQueryTest();
        Users users = new Users();
        users.setUsername("laogeng1'");
        List<Users> list = dynamicConditionQueryTest.queryUsers(users);
        for(Users users2: list){
            System.out.println(users2.getUserid()+" "+users2.getUsername()+" "+users2.getUserage());
        }
    }
}