This is a question relating more to coding standards than anything else.
The problem that I am having is that I am struggling to use my prepared statements as a class/constructor (I am from an informix background btw java is still new to me).
Usually when I code I like to keep scripting out of the main block as much as possible and then call in functions as I need them like in the example I will show. I am also exaggerating the structure with lots of forward slashes.
public class Script {
///////////////////////////////////////////////////////////////// start main
public static void main(String[] args) {
System.out.println("Script Is Starting"); // basic message
classCONN conn = new classCONN(); // connect class
Connection cnct = null; // connect variable
//
try { // try connect
conn.func_driverCheck(); //
cnct = conn.func_dbConnect(); //
} catch(SQLException log) { //
System.out.println(log); //
} //
*i would like to call the prepare*
*statements function once for the*
*rest of the script*
classSQL sql = new classSQL(); // prepare statements
sql.func_prep(cnct); //
users_sel.setString(1, "zoh"); // insert with prepared
users_sel.setString(2, "my"); // statements
users_sel.setString(3, "goodness"); //
row = users_sel.executeQuery(); //
}
///////////////////////////////////////////////////////////////// end main
///////////////////////////////////////////////////////////////// start classes
class classCONN {
public void func_driverCheck() {*code to check driver*}
public Connection func_dbConnect() {*code to connect to db*}
}
class classSQL {
*I would like to prepare my statements here*
public void f_prep(Connection cnct) {
lv_sql = "INSERT INTO users " +
"VALUES(?, ?, ?)";
PreparedStatement users_ins = cnct.prepareStatement(lv_sql);
}
}
///////////////////////////////////////////////////////////////// end classes
}
so my question being is there a way to get code like this to work so that the statements are prepared and then I can executeUpdate them from inside different classes or in the main or anything like that without actually preparing the statements completely in the main block
Here you have greate Example on how to use PreparedStatement.
JDBC PreparedStatement Example – Select List Of The Records
Ok I have come up with an answer to my own question and I would just like to post it here in case anyone can benefit from it or has anything to add to it because that's what this community is for.
public class Prog {
// static variables ---------------------------------------------------
static Connection conn;
static ResultSet row;
// main ---------------------------------------------------------------
public static void main(String[] args) {
// connect to db ---------------------------------------------------
try {
DBConnect cl_conn = new DBConnect();
conn = cl_conn.f_connect();
} catch(Exception log) {
System.out.println("FAIL")
}
// prepare statements ----------------------------------------------
SQLPrep prep = new SQLPrep(conn);
// execute statement 01 --------------------------------------------
try {
prep.users_sel.setInt(1, 2); // pass values to stmnt
row = prep.users_sel.executeQuery(); // execute stmnt
} catch(SQLException log) {
System.out.println("FAIL");
}
}
}
class DBConnect {
***code to connect to db***
}
// all prepared stmnts in one place ----------------------------------------
class SQLPrep {
static PreparedStatement users_sel = null; // select from users
static PreparedStatement access_sel = null; // select from access
try {
sp_sql = "SELECT * FROM USERS WHERE u_id = ?";
users_sel = conn.prepareStatement(sp_sql);
sp_sql = "SELECT * FROM ACCESS WHERE a_id = ?";
access_sel = conn.prepareStatement(sp_sql);
} catch(SQLException log) {
System.out.println("FAIL");
}
}
This may look strange to some people but I find this to be a very clean and tidy way of structuring code (keeping as much code out of the main as possible). Even the block where the statement is executed can be moved into a separate function and would only need to be passed 'prep.users_prep' to work.
Related
My original CRUD Method generates a Prepared Statement and sets the strings based on the parameters given.
public class StatementUtility {
...
public static PreparedStatement getFoo(String bar, Connection conn) {
String query = "SELECT Foo FROM BarTable WHERE Bar = ?";
PreparedStatement pstmt = null;
try {
pstmt = conn.prepareStatement(query);
pstmt.setString(1, bar);
}
catch (SQLException e) {
..
}
return pstmt;
}
...
}
In this Statement the Database which I use is set. I created however a TestDB within my MySQL Server where I would like to test a delete Method:
public static String deleteFoo(List<String> input) {
Connection conn = driver.connectCustomerDB(input);
try(PreparedStatement pstmt = StatementUtility.getFoo(String someString, conn)) {
...
}
}
Here is my Test so far
#RunWith(PowerMockRunner.class)
#PrepareForTest(StatementUtility.class)
public class DBConnectionBTBAdminTest {
#Test
public void deleteTest() {
List<String> testInput = new ArrayList<>();
testInput.add("hello");
testInput.add("World");
Driver driver = new Driver();
Connection conn = driver.connectCustomerDB(testInput);
String query = "FooBarFooBarFooBarFooBarFooBarFooBarFooBarFooBar";
try {
//try mocking the Method within
BDDMockito.given(StatementUtility.getFoo(ArgumentMatchers.anyString(), ArgumentMatchers.anyString(), any(Connection.class))).willReturn(conn.prepareStatement(stringBuilder.toString()));
//call the method I want to test
SomeClass.deleteCategory(testInput, emptyArray);
...
} catch (SQLException e) {
...
}
}
}
The error that I get is a Nullpointer Exception in the Method where I create the PreparedStatement originally, but that is not the point as I do not want to get into this Method at all, but stub it.
I also tried using Mockito instead of BDDMockito (see here: https://stackoverflow.com/a/21116014/8830232)
and using the real values instead of ArgumentMatchers.*
I also tried some other stuff like mocking the Connection
Currently I am using JUnit#4.12, Mockito#2.13.0, powermock#1.7.1
EDIT:
For #glytching answer to work I had to downgrade mockito from 2.x to 1.x. >Dont forget to adjust powermock dependencies in that case
In addition to #PrepareForTest(StatementUtility.class) (which tells PowerMock to prepare this class for testing) you have to enable static mocking for all methods of StatementUtility. You do this by invoking ...
PowerMockito.mockStatic(StatementUtility.class);
... in your test before you attempt to set any expectations on that mock.
For example:
#RunWith(PowerMockRunner.class)
#PrepareForTest(StatementUtility.class)
public class DBConnectionBTBAdminTest {
#Test
public void deleteTest() {
PowerMockito.mockStatic(StatementUtility.class);
List<String> testInput = new ArrayList<>();
testInput.add("hello");
testInput.add("World");
Driver driver = new Driver();
Connection conn = driver.connectCustomerDB(testInput);
String query = "FooBarFooBarFooBarFooBarFooBarFooBarFooBarFooBar";
try {
BDDMockito.given(StatementUtility.getFoo(...)).willReturn(...);
...
} catch (SQLException e) {
...
}
}
}
I can't open my mysql connection at run method inside timertask class. It throws an exception. When I trying to run this class in my mainclass with a timer.scheduleAtFixedRate(backgroundexecution, 0, 5000); method, It is not working. Anyone have any idea about how I can solve this problem?
#Override
public void run() {//here is my run method
backgroundtask obj = new backgroundtask();
try{
Statement statement = obj.openConnection(); //it throws an exception at this line
String mysqlcommand = "Select *from abc";
ResultSet sonuc = statement.executeQuery(mysqlcommand);
while(sonuc.next()){
if(search.contentEquals(sonuc.getString("ssa"))){
System.out.println(sonuc.getString(2));
}
}
statement.close();
}catch(Exception ex) {
System.out.println("fail");
}
}
You need to add this line before you attempt to carry out a db query (it loads the database drivers class);
Class.forName("com.mysql.jdbc.Driver");
If your using a different db driver the string may be different. Also ensure jdbc is in your classpath.
I have an aplication which create a number of query (update or insert) and then each query is executed.
The whole code is working fine but I've saw that my server IO latency is too much during this proccess.
The code execute a loop which is taking arround 1 minute.
Then what I wanted to do is write each query in memory instead to execute it, and then, once I have the whole list of query to execute, use "LOAD DATA LOCAL INFILE" from mysql, which will take less time.
My question is: How can I write all my query (String object) in a "File" or "any other container" in java to use it after the loop?.
#user3283548 This is my example code:
Class1:
import java.util.ArrayList;
public class Class1 {
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
ArrayList<String> Staff=new ArrayList<String>();
Staff.add("tom");
Staff.add("Laura");
Staff.add("Patricia");
for (int x = 0; x < Staff.size(); x++) {
System.out.println(Staff.get(x));
Class2 user = new Class2 (Staff.get(x));
user.checkUser();
}
}
}
Class2:
public class Class2 {
private String user;
public Class2(String user){
this.user=user;
}
public void checkUser() throws Exception{
if (user.equals("tom")){
String queryUser="update UsersT set userStatus='2' where UserName='"+user+"';";
Class3 updateUser = new Class3(queryUser);
updateUser.UpdateQuery();;
}else{
String queryUser="Insert into UsersT (UserName,userStatus)Values('"+user+"','1');";
Class3 updateUser = new Class3(queryUser);
updateUser.InsertQuery();
System.out.println(user+" is not ton doing new insert");
}
}
}
Class3:
public class Class3 {
public String Query;
public Class3(String Query){
this.Query = Query;
}
public void UpdateQuery() throws Exception{
/*// Accessing Driver From Jar File
Class.forName("com.mysql.jdbc.Driver");
//DB Connection
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/default","root","1234567");
String sql =Query;
PreparedStatement pst = con.prepareStatement(sql);*/
System.out.println(Query); //Just to test
//pst.execute();
}
public void InsertQuery() throws Exception{
/*// Accessing Driver From Jar File
Class.forName("com.mysql.jdbc.Driver");
//DB Connection
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/default","root","1234567");
String sql =Query;
PreparedStatement pst = con.prepareStatement(sql);*/
System.out.println(Query); //Just to test
//pst.execute();
}
}
Then, what I wanted to do is create an ArraList in Class1 and use it in Class3 to collect all the queries which has to be executed.
The idea is to execute the list of queries in one time, once the main process is finished, istead to do it for each element within in loop of the Class1. I wanted to do it, because I think it will be take less resource IO from the server HD
Your loop is probably too slow because you're building up Strings using String
I'd hazard a guess you're doing things like
String query = "SELECT * FROM " + variablea + " WHERE + variableb + " = " ...
If you're doing a lot of string concatenation then use StringBuilder as every time you change a string it is actually re-created which is expensive. Simply changing your code to use StringBuilder instead of string will probably cut your loop executed time to a couple of MS. Simply call .toString() method of StringBuilder obj to get the string.
Storing objects
If you want to store anything for later use you should store it in a Collection. If you want a a key-value relationship then use a Map (HashMap would suit you fine). If you just want the values use an List (ArrayList is most popular).
So for example if I wanted to store query strings for later use I would...
Construct the string using StringBuilder.
Put the string (by calling .toString() into a HashMap
Get the query string from the HashMap...
You should never store things on disk if you don't need them to be persistent over application restarts and even then I'd store them in a database not in a file.
Hope this helps.
Thanks
David
EDIT: UPDATE BASED ON YOU POSTING YOUR CODE:
OK this needs some major re-factoring!
I've kept it really simple because I don't have a lot of time to re-write comprehensively.
I've commented where I have made corrections.
Your major issue here is creating objects in loops. You should just create the object once as creating objects is expensive.
I've also corrected other coding issues and replaced the for loop as you shouldn't be writing it like that.I've also renamed the classes to something useful.
I've not tested this so you may need to do some work to get it to work. But this should be a lot faster.
OLD CLASS 1
import java.util.ArrayList;
import java.util.List;
public class StaffChecker {
public static void main(String[] args) throws Exception {
// Creating objects is expensive, you should do this as little as possible
StaffCheckBO staffCheckBO = new StaffCheckBO();
// variables should be Camel Cased and describe what they hold
// Never start with ArrayList start with List you should specific the interface on the left side.
List<String> staffList = new ArrayList<String>();
staffList.add("tom");
staffList.add("Laura");
staffList.add("Patricia");
// use a foreach loop not a (int x = 0 ... ) This is the preffered method.
for (String staffMember : staffList) {
// You now dont need to use .get() you can access the current variable using staffMember
System.out.println(staffMember);
// Do the work
staffCheckBO.checkUser(staffMember);
}
}
}
OLD CLASS 2
/**
* Probably not really any need for this class but I'll assume further business logic may follow.
*/
public class StaffCheckBO {
// Again only create our DAO once...CREATING OBJECTS IS EXPENSIVE.
private StaffDAO staffDAO = new StaffDAO();
public void checkUser(String staffMember) throws Exception{
boolean staffExists = staffDAO.checkStaffExists(staffMember);
if(staffExists) {
System.out.println(staffMember +" is not in database, doing new insert.");
staffDAO.insertStaff(staffMember);
} else {
System.out.println(staffMember +" has been found in the database, updating user.");
staffDAO.updateStaff(staffMember);
}
}
}
OLD CLASS 3
import java.sql.*;
/**
* You will need to do some work to get this class to work fully and this is obviously basic but its to give you an idea.
*/
public class StaffDAO {
public boolean checkStaffExists(String staffName) {
boolean staffExists = false;
try {
String query = "SELECT * FROM STAFF_TABLE WHERE STAFF_NAME = ?";
PreparedStatement preparedStatement = getDBConnection().prepareStatement(query);
// Load your variables into the string in order to be safe against injection attacks.
preparedStatement.setString(1, staffName);
ResultSet resultSet = preparedStatement.executeQuery();
// If a record has been found the staff member is in the database. This obviously doesn't account for multiple staff members
if(resultSet.next()) {
staffExists = true;
}
} catch (SQLException e) {
System.out.println("SQL Exception in getStaff: " + e.getMessage());
}
return staffExists;
}
// Method names should be camel cased
public void updateStaff(String staffName) throws Exception {
try {
String query = "YOUR QUERY";
PreparedStatement preparedStatement = getDBConnection().prepareStatement(query);
// Load your variables into the string in order to be safe against injection attacks.
preparedStatement.setString(1, staffName);
ResultSet resultSet = preparedStatement.executeQuery();
} catch (SQLException e) {
System.out.println("SQL Exception in getStaff: " + e.getMessage());
}
}
public void insertStaff(String staffName) throws Exception {
try {
String query = "YOUR QUERY";
PreparedStatement preparedStatement = getDBConnection().prepareStatement(query);
// Load your variables into the string in order to be safe against injection attacks.
preparedStatement.setString(1, staffName);
ResultSet resultSet = preparedStatement.executeQuery();
} catch (SQLException e) {
System.out.println("SQL Exception in getStaff: " + e.getMessage());
}
}
/**
* You need to abstract the connection logic away so you avoid code reuse.
*
* #return
*/
private Connection getDBConnection() {
Connection connection = null;
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/default", "root", "1234567");
} catch (ClassNotFoundException e) {
System.out.println("Could not find class. DB Connection could not be created: " + e.getMessage());
} catch (SQLException e) {
System.out.println("SQL Exception. " + e.getMessage());
}
return connection;
}
}
I've been doing my homework and I decided to re-write my vote4cash class which manages the mysql for my vote4cash reward system into a new class called MysqlManager. The MysqlManager class I've made needs to allow the Commands class to connect to mysql - done and it needs to allow the Commands class to execute a query - I need help with this part. I've had a lot more progress with the new class that I've made but I'm stuck on one of the last, most important parts of the class, again, allowing the commands class to execute a query.
In my MysqlManager class I have put the code to connects to MySql under
public synchronized static void createConnection() {
Now I just need to put the code that allows the Commands class to execute a query under this as well. I've researched and tried to do this for a while now, but I've had absolutely no luck.
The entire MysqlManager class:
package server.util;
/*
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
*/
import java.sql.*;
import java.net.*;
import server.model.players.Client;//Will be needed eventually so that I can reward players who have voted.
/**
* MySQL and Vote4Cash Manager
* #author Cloudnine
*
*/
public class MysqlManager {
/** MySQL Connection */
public static Connection conn = null;
public static Statement statement = null;
public static ResultSet results = null;
public static Statement stmt = null;
public static ResultSet auth = null;
public static ResultSet given = null;
/** MySQL Database Info */
public static String DB = "vote4gold";
public static String URL = "localhost";
public static String USER = "root";
public static String PASS = "";
public static String driver = "com.mysql.jdbc.Driver"; //Driver for JBDC(Java and MySQL connector)
/** Connects to MySQL Database*/
public synchronized static void createConnection() {
try {
Class.forName(driver);
conn = DriverManager.getConnection(URL + DB, USER, PASS);
conn.setAutoCommit(false);
stmt = conn.createStatement();
Misc.println("Connected to MySQL Database");
}
catch(Exception e) {
//e.printStackTrace();
}
}
public synchronized static void destroyConnection() {
try {
statement.close();
conn.close();
} catch (Exception e) {
//e.printStackTrace();
}
}
public synchronized static ResultSet query(String s) throws SQLException {
try {
if (s.toLowerCase().startsWith("select")) {
ResultSet rs = statement.executeQuery(s);
return rs;
} else {
statement.executeUpdate(s);
}
return null;
} catch (Exception e) {
destroyConnection();
createConnection();
//e.printStackTrace();
}
return null;
}
}
The snippet of my command:
if (playerCommand.equals("claimreward")) {
try {
PreparedStatement ps = DriverManager.getConnection().createStatement("SELECT * FROM votes WHERE ip = hello AND given = '1' LIMIT 1");
//ps.setString(1, c.playerName);
ResultSet results = ps.executeQuery();
if(results.next()) {
c.sendMessage("You have already been given your voting reward.");
} else {
ps.close();
ps = DriverManager.getConnection().createStatement("SELECT * FROM votes WHERE ip = hello AND given = '0' LIMIT 1");
//ps.setString(1, playerCommand.substring(5));
results = ps.executeQuery();
if(results.next()) {
ps.close();
ps = DriverManager.getConnection().createStatement("UPDATE votes SET given = '1' WHERE ip = hello");
//ps.setString(1, playerCommand.substring(5));
ps.executeUpdate();
c.getItems().addItem(995, 5000000);
c.sendMessage("Thank you for voting! You've recieved 5m gold!");
} else {
c.sendMessage("You haven't voted yet. Vote for 5m gold!");
}
}
ps.close();
} catch (Exception e) {
e.printStackTrace();
}
}
return;
How the command works:
When a player types ::commandname(in this case, claimreward), the commands function will be executed. This isn't the entire commands class, just the part that I feel is needed to be posted for my question to be detailed enough for a helpful answer.
Note: I have all my imports.
Note: Mysql connects successfully.
Note: I need to make the above command code snippet able to execute mysql queries.
Note: I prefer the query to be executed straight from the command, instead of from the MysqlManager, but I will do whatever I need to resolve this problem.
I feel that I've described my problem detailed and relevantly enough, but if you need additional information or understanding on anything, tell me and I'll try to be more specific.
Thank you for taking the time to examine my problem. Thanks in advance if you are able to help.
-Alex
Your approach is misguided on many different levels, I can't even start to realize what should be done how here.
1) Don't ever use static class variables unless you know what you do there (and I'm certain, you don't)
2) I assume there is a reason you create your own jdbc connection (e.G. its part of your homework) if not, you shouldn't do that. I see you use DriverManager and PreparedStatement in one part, you should continue to use them.
3) Your approach seems to intend to start with a relative good code base (your command part) and then goes to a very low-level crude approach on database connections (your MysqlManager) unless really necessary and you know what you do, you should stay on the same level of abstraction and aim for the most abstract that fits your needs. (In this case, write MysqlManager the way you wrote Command)
4) In your previous question (that you just assumed everybody here has read, which is not the case) you got the suggestion to redesign your ideas, you should do that. Really, take a class in coding principles learn about anti-patterns and then start from scratch.
So in conclusion: Write at least the MysqlManager again, its fatally broken beyond repair. I'm sorry. Write me an email if you have further questions, I will take my time to see how I can help you. (an#steamnet.de)
Is it possible to store a database connection as a separate class, then call the database objects from a main code? ie;
public class main{
public static void main{
try{
Class.forName("com.jdbc.driver");
Database to = new Database(1,"SERVER1","DATABASE");
Database from = new Database(2,"SERVER2","DATABASE");
String QueryStr = String.format("SELECT * FROM TABLE WHERE Id = %i", to.id)
to.results = sql.executeQuery(QueryStr);
while (to.results.next()) {
String QueryStr = String.format("INSERT INTO Table (A,B) VALUES (%s,%s)",to.results.getString(1),to.results.getString(2));
from.sql.executeQuery("QueryStr");
}
to.connection.close()
from.connection.close()
} catch (Exception ex) {
ex.printStackTrace();
{ finally {
if (to.connection != null)
try {
to.connection.close();
} catch (SQLException x) {
}
if (from.connection != null)
try {
from.connection.close();
} catch (SQLException x) {
}
}
}
public static class Database {
public int id;
public String server;
public String database;
public Connection connection;
public ResultSet results;
public Statement sql;
public Database(int _id, String _server, String _database) {
id = _id;
server = _server;
database = _database;
String connectStr = String.format("jdbc:driver://SERVER=%s;port=6322;DATABASE=%s",server,database);
connection = DriverManager.getConnection(connectStr);
sql = connection.createStatement;
}
}
}
I keep getting a "Connection object is closed" error when I call to.results = sql.executeQuery("SELECT * FROM TABLE"); like the connection closes as soon as the Database is done initializing.
The reason I ask is I have multiple databases that are all about the same that I am dumping into a master database. I thought it would be nice to setup a loop to go through each from database and insert into each to database using the same class. Is this not possible? Database will also contain more methods than shown as well. I am pretty new to java, so hopefully this makes sense...
Also, my code is probably riddled with syntax errors as is, so try not to focus on that.
Connection object is closed doesn't mean that the connection is closed, but that the object relative to the connection is closed (it could be a Statement or a ResultSet).
It's difficult to see from your example, since it has been trimmed/re-arranged, but it looks like you may be trying to use a ResultSet after having re-used its corresponding Statement. See the documentation:
By default, only one ResultSet object per Statement object can be open
at the same time. Therefore, if the reading of one ResultSet object is
interleaved with the reading of another, each must have been generated
by different Statement objects. All execution methods in the Statement
interface implicitly close a statment's current ResultSet object if an
open one exists.
In your example, it may be because autoCommit is set to true by default. You can override this on the java.sql.Connection class. Better yet is to use a transaction framework if you're updating multiple tables.