Develop Reference

Only returning the last element in ArrayList

I've been teaching myself java and I've stuck on a problem that no matter what I do can't seem to solve. I've done some research but all the options provided don't seem to work. Hopefully you guys might be able to teach me something.
I have a .txt file that contains:
AccountName1:Password1
AccountName2:Password2
AccountName3:Password3
AccountName4:Password4
AccountName5:Password5
The elements of the file are then read and inserted into a List:
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public abstract class AccountFileReader {
private static Scanner sc;
public static void main(String[] args) {
try {
// Enables ability to find file in any OS.
String file = File.separator + "some folder name"
+ File.seperator + "AccNamePw.txt";
File f = new File(file);
sc = new Scanner(f);
List<AccountInfo> accounts = new ArrayList<AccountInfo>();
String name = "";
String password = "";
while (sc.hasNext()){
// Reads and checks if there is a new line
String line = sc.nextLine();
// Creates delimiter to make the different elements on file f
String[] details = line.split(":");
// Initializes 1st element
name = details[0];
// Initializes 2nd element
password = details[1];
// Creates new object "a" that has the 2 elements from each line
AccountInfo a = new AccountInfo(name, password);
// Adds the "a" object to the "accounts" List
accounts.add(a);
}
// Iterates list and prints out the list
for(AccountInfo a: accounts){
// The hiccup is in here somewhere. This for loop isn't working in
// a way I think it's supposed to.
// Create new object of the getter, setter class to use in this loop
AccountInfo namPw = new AccountInfo(name, password);
name = namPw.getName();
password = namPw.getPassword();
System.out.println(a.toString() + " " + name
+ " " + password);
}
} catch (FileNotFoundException e) {e.printStackTrace();}
}
}
The getter/setter class is as follows:
public class AccountInfo{
private String name;
private String password;
public AccountInfo(String name, String password) {
this.setName(name);
this.setPassword(password);
}
public void setName(String name) { this.name = name; }
public String getName() { return name; }
public void setPassword(String password) { this.password = password; }
public String getPassword() { return password; }
public String toString(){ return name + " "+ password; }
}
My output is:
AccountName1:Password1 AccountName5:Password5
AccountName2:Password2 AccountName5:Password5
AccountName3:Password3 AccountName5:Password5
AccountName4:Password4 AccountName5:Password5
AccountName5:Password5 AccountName5:Password5
But I want it to return:
AccountName1:Password1 AccountName1:Password1
AccountName2:Password2 AccountName2:Password2
AccountName3:Password3 AccountName3:Password3
AccountName4:Password4 AccountName4:Password4
AccountName5:Password5 AccountName5:Password5
I know that the a.toString() is returning correctly but my namPw.getName() and namPw.getPassword() are only giving me the last element of the List.
What am I not understanding and or missing? How do I get namPw.getName() and namPw.getPassword() to return the List correctly?

The problem is the declaration of nameand password right before the while loop. These variables store the last encountered username and password. When the while loop ends, these variables store the values AccountName5 and Password5 respectively.
When you enter the second for-loop, you first create a new UserAccount with using nameand password which store AccountName5 and Password5.
If you just want to print this list, you do not need to create a copy of the contents of the list. Just do:
for(AccountInfo a : accounts) {
System.out.println(a.toString() + " " + a.getName() + " " + a.getPassword());
}

It's because of this:
for(AccountInfo a: accounts){
**AccountInfo namPw = new AccountInfo(name, password);**
name = namPw.getName();
password = namPw.getPassword();
System.out.println(a.toString() + " " + name
+ " " + password);
You are looping through the AccountInfo objects you already created and then creating a new AccountInfo object and passing in name and password (which get set each time you read in a new line, so the value for them would be the last thing they would be set to when reading the file)
Not sure why you are creating a new AccountInfo object. But in order to get what you want, you'd need to do this:
AccountInfo namPw = new AccountInfo(a.getName(), a.getPassword());

No need to create new object in loop. You are already getting object in a.
Remove object creation line. It is creating object with name and and password which is never going to change as it is outside the loop.
Checkout the following solution:
for(AccountInfo a: accounts){
name = a.getName();
password = a.getPassword();
System.out.println(a.toString() + " " + name + " " + password);
}

Include parameters for spring shell before method

I am working on a Spring Shell project. The tool is a command line tool to manipulate data in a database. There are commands like add user (which adds a record to a table in database). In order to execute any commands the user of the tool has to be connected to the database. I would like to be able to run this all in one line. The user of my tool should be able to write a command like the following.
--database connection string xyz --username abc --password mno add user --username bob --role AA_ADMIN --company Microsoft
Here the three parameters database connection string, username and password are required to run the add user command.
Below I have included some sample code it is from the spring shell reference docs
package commands;
import org.springframework.shell.core.CommandMarker;
import org.springframework.shell.core.annotation.CliAvailabilityIndicator;
import org.springframework.shell.core.annotation.CliCommand;
import org.springframework.shell.core.annotation.CliOption;
import org.springframework.stereotype.Component;
#Component
public class UserManipulation implements CommandMarker {
private boolean simpleCommandExecuted = false;
#CliAvailabilityIndicator({"hw simple"})
public boolean isSimpleAvailable() {
//always available
return true;
}
#CliAvailabilityIndicator({"hw complex", "hw enum"})
public boolean isComplexAvailable() {
if (simpleCommandExecuted) {
return true;
} else {
return false;
}
}
#CliCommand(value = "hw simple", help = "Print a simple hello world message")
public String simple(
#CliOption(key = { "message" }, mandatory = true, help = "The hello world message") final String message,
#CliOption(key = { "location" }, mandatory = false, help = "Where you are saying hello", specifiedDefaultValue="At work") final String location) {
simpleCommandExecuted = true;
return "Message = [" + message + "] Location = [" + location + "]";
}
#CliCommand(value = "hw complex", help = "Print a complex hello world message")
public String hello(
#CliOption(key = { "message" }, mandatory = true, help = "The hello world message") final String message,
#CliOption(key = { "name1"}, mandatory = true, help = "Say hello to the first name") final String name1,
#CliOption(key = { "name2" }, mandatory = true, help = "Say hello to a second name") final String name2,
#CliOption(key = { "time" }, mandatory = false, specifiedDefaultValue="now", help = "When you are saying hello") final String time,
#CliOption(key = { "location" }, mandatory = false, help = "Where you are saying hello") final String location) {
return "Hello " + name1 + " and " + name2 + ". Your special message is " + message + ". time=[" + time + "] location=[" + location + "]";
}
#CliCommand(value = "hw enum", help = "Print a simple hello world message from an enumerated value")
public String eenum(
#CliOption(key = { "message" }, mandatory = true, help = "The hello world message") final MessageType message){
return "Hello. Your special enumerated message is " + message;
}
enum MessageType {
Type1("type1"),
Type2("type2"),
Type3("type3");
private String type;
private MessageType(String type){
this.type = type;
}
public String getType(){
return type;
}
}
}
So currently, hw simple is a command that is required to be executed before running hw complex or hw enum command. I do not want hw simple to be a command instead it the message parameter within the hw simple command should be a parameter that is required as a prerequisite to run hw complex or hw enum. So for example the command that I would like to run is.
--message hw complex --message abc --name1 def --name2 ghi --time 7:98 --location: Seattle
Does anyone know how to do this? If it is not possible to do this I would like to hear that or any alternative ideas if possible.

You have 2 options here:
either make those 3 additional parameters (database, username, password) parameters of each and every command that require them (note that in your particular example, you would need to rename one of those username parameters [the one to connect to the DB, or the one that represents the user to add] as you can't have 2 parameters with the same name obviously).
Use the #CliAvailabilityIndicator approach, similar to what is described in the example, where a first command (maybe named use or connect) first tests the connection with the 3 given parameters and stores them somewhere, so that any further "real" command (such as add user) can use those values.
Also note that you can actually use a combination of the two (i.e. use solution 2 to provide defaults, that may be overridden on a case by case basis by solution 1).
Lastly, please note that you'll never be able to have something like what you describe at the beginning of your question, as command names must be at the beginning and they can't contain -- (options do)

Storing objects in a database java

So I'm working on a program to interface with a file based database. Mostly I'm trying to figure out how to work with it so that I can make objects and store their information in the database so that I can pull the data later.
IE Object Taylor
Name = Taylor
Age = 20
School = Whatever
So that I can get back on and call that information up when queried.
This is an example of an object I want to store. I may be doing this part wrong.
package com.catalyse.db;
public class Taylor implements java.io.Serializable
{
public String name = "Taylor M May";
public int age = 20;
public String school = "UC Boulder";
}
The DB structure I'm using is based on RandomAccessFile and I didn't make it, I'm just trying to figure out how to implement it.
package com.catalyse.db;
import java.util.*;
import java.util.Scanner;
/**
* Simple test class for the RecordsFile example. To run the test,
* set you CLASSPATH and then type "java hamner.dbtest.TestRecords"
*/
public class Run {
static void log(String s) {
System.out.println(s);
}
private static String name()
{
Scanner name = new Scanner(System.in);
String name1 = name.next();
return name1;
}
public static void main (String[] args) throws Exception {
System.out.println(new Date());
Scanner SC = new Scanner(System.in);
log("What would you like to name the database?");
String filename = SC.next();
log("creating records file...");
RecordsFile recordsFile = new RecordsFile(filename+".records", 64);
log("adding a record...");
RecordWriter rw = new RecordWriter("foo.username");
rw.writeObject(new Taylor());
recordsFile.insertRecord(rw);
log("reading record...");
RecordReader rr = recordsFile.readRecord("foo.username");
Taylor name = (Taylor)rr.readObject();
System.out.println("\tlast access was at: " + name.toString());
log("test completed.");
}
}
And here is what I get back from it,
Wed Nov 20 11:56:04 MST 2013
What would you like to name the database?
save3
creating records file...
adding a record...
reading record...
last access was at: com.catalyse.db.Taylor#50aed564
test completed.
My problem is that I want it to return information about the class, not just its name and location in the DB.

You need to override the toString method.
public String toString()
{
StringBuilder sb = new StringBuilder();
sb.append("Name: ");
sb.append(this.name);
//rest of fields
return sb.toString();
}
As a matter of clarity, you are not returning its location in the database. You are getting back the object hashValue + the class name.

At this point
Taylor name = (Taylor)rr.readObject();
You can access whatever information you like in the object, e.g.
Taylor name = (Taylor)rr.readObject();
System.out.println(name.age + ", " + name.name + ", " + name.school);
Alternatively, just add a
public String toString()
{
return name + ", " + age + ", " + school;
}
method in Taylor and then output it like so
Taylor name = (Taylor)rr.readObject();
System.out.println(name);
Now, concerning...
System.out.println("\tlast access was at: " + name.toString());
name.toString() isn't really required. If you append an object to a String then it automatically calls that objects toString() method to get a value.
Lastly, I'd like to note that generally we don't access object members like name, school and age by just accessing them. We generally make them private members then add methods to get and set them, so that we control and can track how they are manipulated.

Java / from string to java code

I have some value which I get in string format from a file.
For example, in the File A I have:
id = 342
name = Jonatan
country = USA
In addition, I have class: person with the next fields:
String id;
String name;
String country;
String grades;
String location;
and I have getter and setter for all the fields.
Now, I want to create a new instance of person, which represents Jonatan.
But - I don't want to update all the field, only the fields I need.
So, what I want to do is the next: get the details from the file, and then for every one do set, and update the correct value. For example, setName(Jonatan). The problems is that my name is in a String format. so I cant do setName - because name is in a string format, and Java doesn't give me the option of call a method in a string format.
There is easy way to it?

You might have a look at Apache BeanUtils
The application is pretty simple - to call setId("42") of a person call:
PropertyUtils.setSimpleProperty(person, "id", "42");

I like #michael_s's answer with BeanUtils. If you want to do it without, you can write:
Person person = new Person();
Properties properties = new Properties();
properties.load(new FileInputStream("the.properties"));
for (Object key : properties.keySet()) {
String field = (String) key;
String setter = "set" + field.substring(0, 1).toUpperCase() + field.substring(1);
Method method = Person.class.getMethod(setter, String.class);
method.invoke(person, properties.get(key));
}
Not that the stream should be closed after using it, and that this short example only works for String properties.

Using java reflection you can determine what methods/fields are available.
You can use this example to pass your key/value pairs into the doReflection method to set the new values of your properties in the instance of the Bean-class.
public class Bean {
private String id = "abc";
public void setId(String s) {
id = s;
}
/**
* Find a method with the given field-name (prepend it with "set") and
* invoke it with the given new value.
*
* #param b The object to set the new value onto
* #param field The name of the field (excluding "set")
* #param newValue The new value
*/
public static void doReflection(Bean b, String field, String newValue) throws NoSuchMethodException,
SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
Class<? extends Bean> c = b.getClass();
Method id = c.getMethod("set" + field, String.class);
id.invoke(b, newValue);
}
public static void main(String... args) throws NoSuchMethodException, SecurityException, IllegalArgumentException,
InvocationTargetException, IllegalAccessException {
Bean bean = new Bean();
System.out.println("ID before: " + bean.id);
doReflection(bean, "Id", "newValue");
System.out.println("ID after: " + bean.id);
// If you have a map of key/value pairs:
Map<String, String> values = new HashMap<String, String>();
for(Entry<String, String> entry : values.entrySet())
doReflection(bean, entry.getKey(), entry.getValue());
}

Creating classes dynamically with Java

I have tried to find information about this but have come up empty handed:
I gather it is possible to create a class dynamically in Java using reflection or proxies but I can't find out how. I'm implementing a simple database framework where I create the SQL queries using reflection. The method gets the object with the database fields as a parameter and creates the query based on that. But it would be very useful if I could also create the object itself dynamically so I wouldn't have the need to have a simple data wrapper object for each table.
The dynamic classes would only need simple fields (String, Integer, Double), e.g.
public class Data {
public Integer id;
public String name;
}
Is this possible and how would I do this?
EDIT: This is how I would use this:
/** Creates an SQL query for updating a row's values in the database.
*
* #param entity Table name.
* #param toUpdate Fields and values to update. All of the fields will be
* updated, so each field must have a meaningful value!
* #param idFields Fields used to identify the row(s).
* #param ids Id values for id fields. Values must be in the same order as
* the fields.
* #return
*/
#Override
public String updateItem(String entity, Object toUpdate, String[] idFields,
String[] ids) {
StringBuilder sb = new StringBuilder();
sb.append("UPDATE ");
sb.append(entity);
sb.append("SET ");
for (Field f: toUpdate.getClass().getDeclaredFields()) {
String fieldName = f.getName();
String value = new String();
sb.append(fieldName);
sb.append("=");
sb.append(formatValue(f));
sb.append(",");
}
/* Remove last comma */
sb.deleteCharAt(sb.toString().length()-1);
/* Add where clause */
sb.append(createWhereClause(idFields, ids));
return sb.toString();
}
/** Formats a value for an sql query.
*
* This function assumes that the field type is equivalent to the field
* in the database. In practice this means that this field support two
* types of fields: string (varchar) and numeric.
*
* A string type field will be escaped with single parenthesis (') because
* SQL databases expect that. Numbers are returned as-is.
*
* If the field is null, a string containing "NULL" is returned instead.
*
* #param f The field where the value is.
* #return Formatted value.
*/
String formatValue(Field f) {
String retval = null;
String type = f.getClass().getName();
if (type.equals("String")) {
try {
String value = (String)f.get(f);
if (value != null) {
retval = "'" + value + "'";
} else {
retval = "NULL";
}
} catch (Exception e) {
System.err.println("No such field: " + e.getMessage());
}
} else if (type.equals("Integer")) {
try {
Integer value = (Integer)f.get(f);
if (value != null) {
retval = String.valueOf(value);
} else {
retval = "NULL";
}
} catch (Exception e) {
System.err.println("No such field: " + e.getMessage());
}
} else {
try {
String value = (String) f.get(f);
if (value != null) {
retval = value;
} else {
retval = "NULL";
}
} catch (Exception e) {
System.err.println("No such field: " + e.getMessage());
}
}
return retval;
}

There are many different ways to achieve this (e.g proxies, ASM), but the simplest approach, one that you can start with when prototyping is:
import java.io.*;
import java.util.*;
import java.lang.reflect.*;
public class MakeTodayClass {
Date today = new Date();
String todayMillis = Long.toString(today.getTime());
String todayClass = "z_" + todayMillis;
String todaySource = todayClass + ".java";
public static void main (String args[]){
MakeTodayClass mtc = new MakeTodayClass();
mtc.createIt();
if (mtc.compileIt()) {
System.out.println("Running " + mtc.todayClass + ":\n\n");
mtc.runIt();
}
else
System.out.println(mtc.todaySource + " is bad.");
}
public void createIt() {
try {
FileWriter aWriter = new FileWriter(todaySource, true);
aWriter.write("public class "+ todayClass + "{");
aWriter.write(" public void doit() {");
aWriter.write(" System.out.println(\""+todayMillis+"\");");
aWriter.write(" }}\n");
aWriter.flush();
aWriter.close();
}
catch(Exception e){
e.printStackTrace();
}
}
public boolean compileIt() {
String [] source = { new String(todaySource)};
ByteArrayOutputStream baos= new ByteArrayOutputStream();
new sun.tools.javac.Main(baos,source[0]).compile(source);
// if using JDK >= 1.3 then use
// public static int com.sun.tools.javac.Main.compile(source);
return (baos.toString().indexOf("error")==-1);
}
public void runIt() {
try {
Class params[] = {};
Object paramsObj[] = {};
Class thisClass = Class.forName(todayClass);
Object iClass = thisClass.newInstance();
Method thisMethod = thisClass.getDeclaredMethod("doit", params);
thisMethod.invoke(iClass, paramsObj);
}
catch (Exception e) {
e.printStackTrace();
}
}
}

It is possible to generate classes (via cglib, asm, javassist, bcel), but you shouldn't do it that way. Why?
the code that's using the library should expect type Object and get all the fields using reflection - not a good idea
java is statically typed language, and you want to introduce dynamic typing - it's not the place.
If you simply want the data in an undefined format, then you can return it in an array, like Object[], or Map<String, Object> if you want them named, and get it from there - it will save you much trouble with unneeded class generation for the only purpose of containing some data that will be obtained by reflection.
What you can do instead is have predefined classes that will hold the data, and pass them as arguments to querying methods. For example:
public <T> T executeQuery(Class<T> expectedResultClass,
String someArg, Object.. otherArgs) {..}
Thus you can use reflection on the passed expectedResultClass to create a new object of that type and populate it with the result of the query.
That said, I think you could use something existing, like an ORM framework (Hibernate, EclipseLink), spring's JdbcTemplate, etc.

This is possible, but (I believe) you need something like ASM or BCEL.
Alternately, you could use something with more power (like Groovy).

It will take a couple of minutes to create a data model class for each table, which you can easily map to the database with an ORM like Hibernate or by writing your own JDBC DAOs. It is far easier than delving deeply into reflection.
You could create a utility that interrogates the database structure for a table, and creates the data model class and DAO for you. Alternatively you could create the model in Java and create a utility to create the database schema and DAO from that (using reflection and Java 5 Annotations to assist). Don't forget that javaFieldNames are different from database_column_names typically.

Recently I needed to create about 200 simple classes from medatata (objects filled with static data) and I did it through the open source burningwave library, with the following scenario:
The classes needed to have a certain prefix in the name, for example "Registro "*.java;
The classes needed to extend from a superclass Registro.java
The classes needed to contain JPA annotations like #Entity, #Column (in attributes), Lombok annotations and custom annotations.
Here is the link to the repository with the complete project: https://github.com/leandrosoares6/criacao-classes-entidade-efd
Here is the code snippet responsible for creating the classes:
public class RegistrosClassFactory {
private static final String PACOTE = "com.example.demo.model.registros";
private static final String SCHEMA = "MY_SCHEMA";
private static final String PREFIXO = "Registro";
static void criaRegistros() {
List<RegistroTest> registros = RegistroMetadataFactory.criaMetadados();
criaClasses(registros);
}
private static void criaClasses(List<RegistroTest> registros) {
for (RegistroTest registroTest : registros) {
UnitSourceGenerator gerador = UnitSourceGenerator.create(PACOTE);
ClassSourceGenerator registro = ClassSourceGenerator
.create(TypeDeclarationSourceGenerator.create(PREFIXO + registroTest.getNome()))
.addModifier(Modifier.PUBLIC)
.addAnnotation(AnnotationSourceGenerator.create(Getter.class))
.addAnnotation(AnnotationSourceGenerator.create(Setter.class))
.addAnnotation(AnnotationSourceGenerator.create(NoArgsConstructor.class))
.addAnnotation(AnnotationSourceGenerator.create(ToString.class))
.addAnnotation(AnnotationSourceGenerator.create(Entity.class))
.addAnnotation(AnnotationSourceGenerator.create(Table.class)
.addParameter("name",
VariableSourceGenerator.create(String.format("\"%s\"",
registroTest.getNomeTabelaBd())))
.addParameter("schema", VariableSourceGenerator
.create(String.format("\"%s\"", SCHEMA))));
criaColunas(registroTest.getCampos(), registro);
registro.addConstructor(FunctionSourceGenerator.create().addModifier(Modifier.PUBLIC)
.addParameter(VariableSourceGenerator.create(String.class, "linha"))
.addBodyCodeLine("super(linha);")).expands(Registro.class);
gerador.addClass(registro);
// System.out.println("\nRegistro gerado:\n" + gerador.make());
String caminhoPastaRegistros = System.getProperty("user.dir") + "/src/main/java/";
gerador.storeToClassPath(caminhoPastaRegistros);
}
}
private static void criaColunas(List<Campo> campos, ClassSourceGenerator registro) {
for (Campo campo : campos) {
VariableSourceGenerator field = VariableSourceGenerator
.create(TypeDeclarationSourceGenerator.create(String.class),
campo.getNomeAtributo())
.addModifier(Modifier.PRIVATE)
.addAnnotation(AnnotationSourceGenerator.create(Column.class)
.addParameter("name", VariableSourceGenerator
.create(String.format("\"%s\"", campo.getNome())))
)
.addAnnotation(AnnotationSourceGenerator.create(Indice.class).addParameter(
"valor",
VariableSourceGenerator.create(String.valueOf(campo.getSequencial()))));
if (campo.getNome().equals("ID")) {
field.addAnnotation(AnnotationSourceGenerator.create(Id.class));
}
if (campo.getEId()) {
field.addAnnotation(AnnotationSourceGenerator.create(CampoTipoId.class));
}
if (campo.getEData()) {
field.addAnnotation(AnnotationSourceGenerator.create(CampoTipoData.class));
}
if (campo.getEDataPart()) {
field.addAnnotation(AnnotationSourceGenerator.create(CampoTipoDataPart.class));
}
registro.addField(field);
}
}
}

I'm aware of the performance drawback of reflection but for my little project I needed this and I created a project lib which converts JSON to Java and then finally .class in JVM context.
Anyone need such thing can have a look into my open source solution, which requires JDK to compile the code.
https://medium.com/#davutgrbz/the-need-history-c91c9d38ec9?sk=f076487e78a1ff5a66ef8eb1aa88f930