here is code for main
public static void main(String[] args) {
Container container= new Container();
Serializator serializator = new Serializator();
container.setvalue("1st val");
serializator.serialization(container);
}
here is code for container
public class Container implements Serializable {
private static final long serialVersionUID = 1L;
/**
* Holds the elements of a container.
*/
private String[] values;
public String[] getvalue() {
return values;
}
public void setvalue(String[] values) {
this.values=values;
}
}
here is code for a serializator
public class Serializator {
public boolean serialization(Container container) {
boolean flag=false;
File file= new File("C:/conatiner.data");
ObjectOutputStream oos = null;
try {
FileOutputStream fos= new FileOutputStream(file);
if(fos != null) {
oos= new ObjectOutputStream(fos);
oos.writeObject(container);
flag=true;
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if(oos != null) {
try {
oos.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
return flag;
}
}
Well, the program should be working in a following way: you create a container that has an array of strings,(you can set the values in it) and then the program must serialize it. but the problem is that the tutorial worked with the String value, but not the String[] one. how can i make it understand the String[] value and insert it?
The crashlog is the following
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
The method setvalue(String[]) in the type Container is not applicable for the arguments (String)
at ua.khpi.oop.taradai06.program6.main(program6.java:7)
"container.setvalue("1st val");"
First, let's focus on the bug:
In the container, you promised you will send an array of string in the function setValue, but you are sending a single string.
There are two things you could do;
keep the container code as it is and send array of strings from main
Change the container code and let setValue get a single string value and add it to the values array
And you main question related with serialisation please check that post
In order to accept both String and String[] as an input parameter to Container::setvalue method, the varargs should be used, then a single String is accepted as an array consisting of one element.
Also, Java naming conventions for getters/setters of Java Beans specify to capitalize the property names after get/set verb: Getter and setter method names are composed of the word get or set, respectively, plus the property name with the first character of each word capitalized, so the methods should be names as getValues/setValues:
// Container class
public void setValues(String... values) {
this.values = values;
}
Then this method can be invoked as follows without additional overloading:
container.setValues(); // empty array new String[0]
container.setValues("a string"); // new String[1]{"a string"}
container.setValues("a", "b"); // new String[2]{"a", "b"}
container.setValues(new String[]{"1", "2", "3"}); // common array
If you promised you'll use the String[] parameter, then you should note that.
The following version of using setvalue does this work perfectly
container.setvalue(new String[] {"1st val","2nd val","3rd val"});
OK I hope I helped you look in the class "Container" in "setvalue" function, you gived it the parameter "1st value"(Its one string) but it needs a String array. So you can replace your code with this:
main class:
public class main {
public static void main(String[] args) {
Container container= new Container();
Serializator serializator = new Serializator();
container.setvalue("1st value", 0);
serializator.serialization(container);
}
}
Container class:
import java.io.Serializable;
public class Container implements Serializable {
private static final long serialVersionUID = 1L;
/**
* Holds the elements of a container.
*/
int AnyNumberYouWant = 100;
private String[] values = new String[AnyNumberYouWant];
public String[] getvalue() {
return values;
}
public void setvalue(String value, int index) {
this.values[index]=value;
}
}
Serializator class
import java.io.*;
public class Serializator {
public boolean serialization(Container container) {
boolean flag=false;
File file= new File("C:/Container/container.data");
ObjectOutputStream oos = null;
try {
FileOutputStream fos= new FileOutputStream(file);
if(fos != null) {
oos= new ObjectOutputStream(fos);
oos.writeObject(container);
flag=true;
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if(oos != null) {
try {
oos.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
return flag;
}
}
And I solved another errors that was there in the code. So I tried it and worked correctly. I hope that I helped you.
Related
I have a messages.properties file that contains all string messages used in my application.
I would like to bind these messages to a java class fields and use directly in other classes.
Can this be achieved without using NLS? By some approach in javafx? Because I do not want to add eclipse dependency in UI classes.
Java provides property file reading capability right from the box. You can do adjustment to suit your actual use-case.
For example:
public final class Messages {
private Messages() {
loadFile();
}
private static final class ThreadSafeSingleton {
private static final Messages INSTANCE = new Messages();
}
public static Messages getInstance() {
return ThreadSafeSingleton.INSTANCE;
}
private final Properties props = new Properties();
private void loadFile() {
InputStream is = null;
try {
is = new FileInputStream("messages.properties");
props.load(is);
} catch (IOException ex) {
ex.printStackTrace();
} finally {
if (is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public String getMessage(String key) {
if (key == null && key.isEmpty()) return "";
return props.getProperty(key);
}
}
Edit
In order to use these values as if it is a constant, you need to pretty much make everything static:
public final class Messages {
private Messages() {} // Not instantiable
private static final Properties props = loadFile(); // Make sure this static field is at the top
public static final String FOO = getMessage("foo");
public static final String BAR = getMessage("bar");
private static Properties loadFile() {
final Properties p = new Properties();
InputStream is = null;
try {
is = new FileInputStream("messages.properties");
p.load(is);
} catch (IOException ex) {
ex.printStackTrace();
} finally {
if (is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return p;
}
public static String getMessage(String key) {
if (key == null && key.isEmpty()) return "";
return props.getProperty(key);
}
}
Be warned again, the Properties field must always be the top-most field declared in the class, because the class loader will load the fields top-down for all static fields whose value is computed at runtime (i.e. set by a static method).
Another point, this example does not handles what happens if the file is not file - it simply returns a Properties that has no value.
I have a class Logger that uses 3 arraysas xhared variables
The arrays are initialized in the contructor
but when accessing them in any other method of the class, I get a
NullPointerException.
I need to know the reason and the solution.
Please see comments in the code.
file Logger.java
package logger_010.standard;
import java.io.FileOutputStream;
import java.io.PrintStream;
public class Logger {
// declaration
private FileOutputStream[] files;
private PrintStream[] pss;
private String[] messages;
public Logger() {
// initialisation
try {
FileOutputStream[] files = {
new FileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger0.log"),
new FileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger1.log"),
new FileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger2.log"),
};
PrintStream[] pss = {
new PrintStream(files[0]),
new PrintStream(files[1]),
new PrintStream(files[2]),
};
String[] messages = {
new String ("Write error message to log file 0"),
new String ("Write error message to log file 1 + user"),
new String ("Write error message to log file 2 + user+ email"),
};
// Arrays instanciation is OK
System.out.println(files[0].toString());
System.out.println(files[1].toString());
System.out.println(files[2].toString());
System.out.println(pss[0].toString());
System.out.println(pss[1].toString());
System.out.println(pss[2].toString());
System.out.println(messages[0].toString());
System.out.println(messages[1].toString());
System.out.println(messages[2].toString());
System.out.println("++++++++++++");
} catch (Exception e) {
System.out.println("Exception " + e.getMessage());
} finally {
}
}
public void LogMessage(int level) {
// Here I get a Null pointer exception
System.out.println(files[0].toString());
System.out.println(files[1].toString());
System.out.println(files[2].toString());
System.out.println(pss[0].toString());
System.out.println(pss[1].toString());
System.out.println(pss[2].toString());
System.out.println(messages[0].toString());
System.out.println(messages[1].toString());
System.out.println(messages[2].toString());
System.out.println("++++++++++++");
// PrintStream[] files = OpenFiles();
WriteLogMessage(this.getPss(), level);
CloseFiles(pss);
}
private void CloseFiles(PrintStream[] pss2) {
// TODO Auto-generated method stub
}
private PrintStream[] OpenFiles() {
// TODO Auto-generated method stub
return null;
}
private void WriteLogMessage(PrintStream[] files, int level) {
this.getPss()[level].println(messages[level]);
this.getPss()[level].flush();
}
public FileOutputStream[] getFiles() {
return files;
}
public void setFiles(FileOutputStream[] files) {
this.files = files;
}
public PrintStream[] getPss() {
return pss;
}
public void setPss(PrintStream[] pss) {
this.pss = pss;
}
public String[] getMessages() {
return messages;
}
public void setMessages(String[] messages) {
this.messages = messages;
}
}
this is the file containing the main function
package logger_010.standard;
public class Start {
public static void main(String[] args) {
// TODO Auto-generated method stub
Logger l = new Logger();
for (int i = 0; i < 15; i++) {
int level = i % 2;
l.LogMessage(level);
}
}
}
You are declare a new files, message, pss variable inside constructor instead of using the variable already created of class => when using in the LogMessage method, it use the variable not init => cause the error
You never actualy bind your class attribut with the object you define in your constructor.
By defining FileOutputStream[] files = ... instead of files = ..., which is your object attribut, you are just making a local variable whose scope is only inside the constructor.
Your constructor should be :
public Logger() {
// initialisation
try {
files = {
new FileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger0.log"),
new FileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger1.log"),
new FileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger2.log"),
};
pss = {
new PrintStream(files[0]),
new PrintStream(files[1]),
new PrintStream(files[2]),
};
messages = {
new String ("Write error message to log file 0"),
new String ("Write error message to log file 1 + user"),
new String ("Write error message to log file 2 + user+ email"),
};
// Arrays instanciation is OK
System.out.println(files[0].toString());
System.out.println(files[1].toString());
System.out.println(files[2].toString());
System.out.println(pss[0].toString());
System.out.println(pss[1].toString());
System.out.println(pss[2].toString());
System.out.println(messages[0].toString());
System.out.println(messages[1].toString());
System.out.println(messages[2].toString());
System.out.println("++++++++++++");
} catch (Exception e) {
System.out.println("Exception " + e.getMessage());
} finally {
}
}
If I initialize the FileOutputStream array with a sub class of FileOutputStream and a constructor that throws a FileNotFoundException I get this compilation error
"Default constructor cannot handle exception type FileNotFoundException thrown by implicit super constructor. Must define an explicit constructor".
I finally solved the problem by using a function (makeFileOutputStream) and this function call the FileOutputStream constructor in a try/catch block
here is the code for my class Blogger
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintStream;
public class Logger {
// declarations
private FileOutputStream[] files = {
makeFileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger0.log"),
makeFileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger1.log"),
makeFileOutputStream("G:\\Users\\TarekEZZAT\\Documents\\logs\\logger2.log"),
};
private PrintStream[] pss = {
new PrintStream(files[0]),
new PrintStream(files[1]),
new PrintStream(files[2]),
};
private String[] messages = {
new String("Write error message to log file 0"),
new String("Write error message to log file 1 + user"),
new String("Write error message to log file 2 + user+ email"),
};
private FileOutputStream makeFileOutputStream(String string) {
// TODO Auto-generated method stub
FileOutputStream fos = null;
try {
fos = new FileOutputStream(string);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return fos;
}
public void LogMessage(int level) {
WriteLogMessage(this.getPss(), level);
}
public void CloseFile(PrintStream[] files, int level){
// TODO Auto-generated method stub
this.getPss()[level].close();
}
private void WriteLogMessage(PrintStream[] files, int level) {
this.getPss()[level].println(messages[level]);
this.getPss()[level].flush();
}
// Getters and Setters
public FileOutputStream[] getFiles() {
return files;
}
public void setFiles(FileOutputStream[] files) {
this.files = files;
}
public PrintStream[] getPss() {
return pss;
}
public void setPss(PrintStream[] pss) {
this.pss = pss;
}
public String[] getMessages() {
return messages;
}
public void setMessages(String[] messages) {
this.messages = messages;
}
}
I have to write a different class to read a file of different kind. Now project is deployed on client side. And we have to give support to new files. so we have to create a new class and also modify in service class to create a new object of newly added class. Writing a new class for new type of class is fine. But I do not want to change service class each time. Is there any solution for this kind of problem? Thanks in advance.
Update 1: here is code of service class
#Service("StockistServiceImpl")
public class StockistServiceImpl implements StockistService {
#Override
#Transactional(propagation = Propagation.REQUIRED,rollbackFor=Exception.class)
public JSONArray saveStockistOrder(Integer stockistId,
MultipartFile[] orderFile, String orderNumber, String orderDate,
String partyCode,String order,Integer userId)
{
List<Pair<String, Integer>> charList = new ArrayList<Pair<String, Integer>>();
Properties code1 = new Properties();
try {
code.load(StockistServiceImpl.class.getClassLoader().getResourceAsStream("categoryOfFile.properties"));
}
catch (IOException e) {
//System.out.println("error in loading divisionNamePdfCode.properties");
e.printStackTrace();
}
String readDuelListedTxtFile = code.getProperty("readDuelListedTxtFile");
String readStartLineLengthForOrderTxtFile = code.getProperty("readStartLineLengthForOrderTxtFile");
String ReadFileWithNoStartLineTxtFile = code.getProperty("ReadFileWithNoStartLineTxtFile");
String ReadStartLineLengthForQtySingleListTxtFile = code.getProperty("ReadStartLineLengthForQtySingleListTxtFile");
if (readDuelListedTxtFile.contains(partyCode
.trim())) {
charList.addAll(dualListText
.readDuelListedTxtFile(
fileName, codeDetails));
}
else if (readStartLineLengthForOrderTxtFile.contains(partyCode
.trim())) {
charList.addAll(lineLength
.readStartLineLengthForOrderTxtFile(
fileName, codeDetails));
}
else if (ReadFileWithNoStartLineTxtFile.contains(partyCode
.trim())) {
T_FileWithNoStartLine noStartLine = new T_FileWithNoStartLine();
charList.addAll(noStartLine
.readFileWithNoStartLineTxtFile(
fileName, codeDetails));
}
else if (ReadStartLineLengthForQtySingleListTxtFile.contains(partyCode
.trim())) {
T_StartLineLengthForQtySingleList noStartLine = new T_StartLineLengthForQtySingleList();
charList.addAll(noStartLine
.readStartLineLengthForQtySingleListTxtFile(
fileName, codeDetails));
}
}
Update 2: here is property file from where we know that what is file type for a stockist.
#fileType,stockistCode
fileType1=ST001,ST009
fileType2=ST002,ST005,ST006
fileType3=ST003,ST007
fileType4=ST004,ST008
and i want to add a new property file like this to map a file type with class name so if a new class is added and then we will not have to edit service class.
#fileType,fullyqualifiedclassName
fileType1=FullyQualifiedClassName1
fileType2=FullyQualifiedclassName2
fileType3=FullyQualifiedClassName3
fileType4=FullyQualifiedclassName4
Separate the creation of the file readers objects and the service class.
public class BuildFileReader() {
FileReader getReader(String xyz) {
FileReader reader;
...
your logic
reader = new WhatEverReaderYouWant();
...
return reader;
}
}
The service class simply asks the BuildFileReader which FileReader to use and doesn't need to change anymore.
public class StockistServiceImpl {
...
BuildFileReader bfr = new BuildFileReader();
FileReader fileReader = bfr.getReader(xyz);
fileReader.readFile(fileName, codeDetails);
...
}
If you need only one type of file reader per client, you could configure your BuildFileReader for each client.
If you need more than one type of file reader per client, define an interface for each type an add a getReaderXYZ() function for each needed type in BuildFileReader.
Instance can be created at runtime using reflection in java, please have a look at below post:
Creating an instance using the class name and calling constructor
Finally after doing some code changes and adding property file for mapping class names with property of file here is the code and working fine.
#Service("StockistServiceImpl")
public class StockistServiceImpl implements StockistService {
List<Pair<String, Integer>> charList = new ArrayList<Pair<String, Integer>>();
Map<String,String> mapTxtFile = new HashMap<String, String>();
Properties fileTypeProperties = new Properties();
Properties matchClassNameProperties = new Properties();
try {
fileTypeProperties.load(StockistServiceImpl.class.getClassLoader().getResourceAsStream("fileTypeProperties.properties"));
}
catch (IOException e) {
//e.printStackTrace();
}
try {
matchClassNameProperties.load(StockistServiceImpl.class.getClassLoader().getResourceAsStream("matchClassNameProperties.properties"));
}
catch (IOException e) {
//e.printStackTrace();
}
for (String key : fileTypeProperties.stringPropertyNames()) {
String value = fileTypeProperties.getProperty(key);
mapTxtFile.put(key, value);
if(value.contains(partyCode.trim())){
String className = matchClassNameProperties.getProperty(key);
try {
Class clazz = Class.forName(className);
try {
TxtFile objToReadTxtFile = (TxtFile) clazz.newInstance();
charList= objToReadTxtFile.readTxtFile(fileName, codeDetails);
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}else{
//read normally else block
}
}
}
Now it is working fine.But for that i created an interface for reading txt file which has readTxtFile method. and all other classes now implement this interface.
so i've been sitting above this code for a while , ready the NullPointerException threads, and still can't figure out what is going wrong in my code, so i turn to you.
public class Main {
public static void main(String[] args){
/* Making catalog, loading last state */
Collection catalog = new Collection();
try {
catalog.readFromFile();
} catch (ClassNotFoundException | IOException e) {
e.printStackTrace();
}
catalog.addShip(new Ship("ABC123", "John", "Suzuki", 50));
}
}
And my Collection class looks like this:
public class Collection {
private List<Ship> shipList;
private String fileName = "catalog.txt";
private int income;
private int space;
public Collection() {
shipList = new ArrayList<Ship>();
income = 0;
space = 500;
File f = new File("catalog.txt");
if(!f.exists()) {
try {
f.createNewFile();
writeToFile();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void addShip(Ship SHIP){
space -= SHIP.LENGTH;
income += SHIP.COST;
shipList.add(SHIP);
}
public Ship getShip(int INDEX){
return shipList.get(INDEX);
}
public void writeToFile() throws IOException {
FileOutputStream f = new FileOutputStream(fileName);
ObjectOutputStream out = new ObjectOutputStream(f);
out.writeObject(shipList);
out.close();
}
#SuppressWarnings("unchecked")
public void readFromFile() throws IOException, ClassNotFoundException {
FileInputStream f = new FileInputStream(fileName);
ObjectInputStream in = new ObjectInputStream(f);
shipList = (ArrayList<Ship>)in.readObject();
in.close();
}
public int getIncome(){
return income;
}
public int getSpace(){
return space;
}
}
My problem is, when i call in main catalog.addship() i get nullptr error. After following the console errors, it says i get the nullptrexc when i call the addShip() on the catalog, following from there i get the error when i add() a Ship to the Collection's shipList. So what i concluded, it is because the shipList in the Collection is uninitialized. But in the constructor i write shipList = new ArrayList<Ship>(); so it is clearly initialized.
The exception stacktrace is the following:
Exception in thread "main" java.lang.NullPointerException
at collection.Collection.addShip(Collection.java:31)
at main.Main.main(Main.java:100)
In your main method, you initialize the ArrayList properly. But then, you make a
catalog.readFromFile()
call. In the readFromFile() method, you re-initialize the ArrayList
shipList = (ArrayList<Ship>)in.readObject();
the in.readObject() is returning null. That is why your shipList variable is null.
Hope this helps!
How are the values of static variables persisted during serialization(If at all persisted). I have read similar questions on stack where it says that static variables are inherently transient i.e their state or current values is not serialized.
I was just doing a very simple example where i serialized a class and saved it to a file and then again reconstructed the class from the file.Surprisingly I find that the value of the static variable at and when the serialization happened is saved.
How does this happen. Is this because the class template along with it's instance information is saved during serialization. Here is the code snippet -
public class ChildClass implements Serializable, Cloneable{
/**
*
*/
private static final long serialVersionUID = 5041762167843978459L;
private static int staticState;
int state = 0;
public ChildClass(int state){
this.state = state;
staticState = 10001;
}
public String toString() {
return "state" + state + " " + "static state " + staticState;
}
public static void setStaticState(int state) {
staticState = state;
}
and here is my main class
public class TestRunner {
/**
* #param args
*/
public static void main(String[] args) {
new TestRunner().run();
}
public TestRunner() {
}
public void run() {
ChildClass c = new ChildClass(101);
ChildClass.setStaticState(999999);
FileOutputStream fo = null;
ObjectOutputStream os = null;
File file = new File("F:\\test");
try {
fo = new FileOutputStream(file);
os = new ObjectOutputStream(fo);
os.writeObject(c);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
try {
if(null != os)os.close();
if(null != fo) fo.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
FileInputStream fi = null;
ObjectInputStream ois = null;
ChildClass streamed;
try {
fi = new FileInputStream(file);
ois = new ObjectInputStream(fi);
Object o = ois.readObject();
if(o instanceof ChildClass){
streamed = (ChildClass)o;
//ChildClass cloned = streamed.clone();
System.out.println(streamed.toString());
}
} catch (IOException | ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
try {
if(null != ois)ois.close();
if(null != fi) fi.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
Note : There is nothing wrong with the code. I just am wondering how the value of the static variable 'staticState' in the class 'ChildClass' gets saved. Will the state be saved if i transmit this serialized data over a network then
The static field value was not serialized. The output is printing the new value of the static field simply because you modified it to 999999 but you never reset its value to the old one before de-serizalizing. Since the field is static, the new value is reflected in any instance of ChildClass.
To properly assert that the field is not serialized, reset the value to 10001 before de-serializing the object, and you will notice that its value is not 999999.
...
ChildClass.setStaticState(10001);
FileInputStream fi = null;
ObjectInputStream ois = null;
ChildClass streamed;
...
// when de-serializing, the below will print "state101 static state 10001"
System.out.println(streamed.toString());