I have a class defined as follows:
public class Person {
private String name;
// constructor and getter/setter omitted
}
I tried to print an instance of my class:
System.out.println(myPerson);
but I got the following output: com.foo.Person#2f92e0f4.
A similar thing happened when I tried to print an array of Person objects:
Person[] people = //...
System.out.println(people);
I got the output: [Lcom.foo.Person;#28a418fc
What does this output mean? How do I change this output so it contains the name of my person? And how do I print collections of my objects?
Note: this is intended as a canonical Q&A about this subject.
Background
All Java objects have a toString() method, which is invoked when you try to print the object.
System.out.println(myObject); // invokes myObject.toString()
This method is defined in the Object class (the superclass of all Java objects). The Object.toString() method returns a fairly ugly looking string, composed of the name of the class, an # symbol and the hashcode of the object in hexadecimal. The code for this looks like:
// Code of Object.toString()
public String toString() {
return getClass().getName() + "#" + Integer.toHexString(hashCode());
}
A result such as com.foo.MyType#2f92e0f4 can therefore be explained as:
com.foo.MyType - the name of the class, i.e. the class is MyType in the package com.foo.
# - joins the string together
2f92e0f4 the hashcode of the object.
The name of array classes look a little different, which is explained well in the Javadocs for Class.getName(). For instance, [Ljava.lang.String means:
[ - an single-dimensional array (as opposed to [[ or [[[ etc.)
L - the array contains a class or interface
java.lang.String - the type of objects in the array
Customizing the Output
To print something different when you call System.out.println(myObject), you must override the toString() method in your own class. Here's a simple example:
public class Person {
private String name;
// constructors and other methods omitted
#Override
public String toString() {
return name;
}
}
Now if we print a Person, we see their name rather than com.foo.Person#12345678.
Bear in mind that toString() is just one way for an object to be converted to a string. Typically this output should fully describe your object in a clear and concise manner. A better toString() for our Person class might be:
#Override
public String toString() {
return getClass().getSimpleName() + "[name=" + name + "]";
}
Which would print, e.g., Person[name=Henry]. That's a really useful piece of data for debugging/testing.
If you want to focus on just one aspect of your object or include a lot of jazzy formatting, you might be better to define a separate method instead, e.g. String toElegantReport() {...}.
Auto-generating the Output
Many IDEs offer support for auto-generating a toString() method, based on the fields in the class. See docs for Eclipse and IntelliJ, for example.
Several popular Java libraries offer this feature as well. Some examples include:
ToStringBuilder from Apache Commons Lang
MoreObjects.ToStringHelper from Google Guava
#ToString annotation from Project Lombok
Printing groups of objects
So you've created a nice toString() for your class. What happens if that class is placed into an array or a collection?
Arrays
If you have an array of objects, you can call Arrays.toString() to produce a simple representation of the contents of the array. For instance, consider this array of Person objects:
Person[] people = { new Person("Fred"), new Person("Mike") };
System.out.println(Arrays.toString(people));
// Prints: [Fred, Mike]
Note: this is a call to a static method called toString() in the Arrays class, which is different to what we've been discussing above.
If you have a multi-dimensional array, you can use Arrays.deepToString() to achieve the same sort of output.
Collections
Most collections will produce a pretty output based on calling .toString() on every element.
List<Person> people = new ArrayList<>();
people.add(new Person("Alice"));
people.add(new Person("Bob"));
System.out.println(people);
// Prints [Alice, Bob]
So you just need to ensure your list elements define a nice toString() as discussed above.
I think apache provides a better util class which provides a function to get the string
ReflectionToStringBuilder.toString(object)
Every class in Java has the toString() method in it by default, which is called if you pass some object of that class to System.out.println(). By default, this call returns the className#hashcode of that object.
{
SomeClass sc = new SomeClass();
// Class # followed by hashcode of object in Hexadecimal
System.out.println(sc);
}
You can override the toString method of a class to get different output. See this example
class A {
String s = "I am just a object";
#Override
public String toString()
{
return s;
}
}
class B {
public static void main(String args[])
{
A obj = new A();
System.out.println(obj);
}
}
In Eclipse,
Go to your class,
Right click->source->Generate toString();
It will override the toString() method and will print the object of that class.
I prefer to use a utility function which uses GSON to de-serialize the Java object into JSON string.
/**
* This class provides basic/common functionalities to be applied on Java Objects.
*/
public final class ObjectUtils {
private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
private ObjectUtils() {
throw new UnsupportedOperationException("Instantiation of this class is not permitted in case you are using reflection.");
}
/**
* This method is responsible for de-serializing the Java Object into Json String.
*
* #param object Object to be de-serialized.
* #return String
*/
public static String deserializeObjectToString(final Object object) {
return GSON.toJson(object);
}
}
In intellij you can auto generate toString method by pressing alt+inset and then selecting toString() here is an out put for a test class:
public class test {
int a;
char b;
String c;
Test2 test2;
#Override
public String toString() {
return "test{" +
"a=" + a +
", b=" + b +
", c='" + c + '\'' +
", test2=" + test2 +
'}';
}
}
As you can see, it generates a String by concatenating, several attributes of the class, for primitives it will print their values and for reference types it will use their class type (in this case to string method of Test2).
By default, every Object in Java has the toString() method which outputs the ObjectType#HashCode.
If you want more meaningfull information then you need to override the toString() method in your class.
public class Person {
private String name;
// constructor and getter/setter omitted
// overridding toString() to print name
public String toString(){
return name;
}
}
Now when you print the person object using System.out.prtinln(personObj); it will print the name of the person instead of the classname and hashcode.
In your second case when you are trying to print the array, it prints [Lcom.foo.Person;#28a418fc the Array type and it's hashcode.
If you want to print the person names, there are many ways.
You could write your own function that iterates each person and prints
void printPersonArray(Person[] persons){
for(Person person: persons){
System.out.println(person);
}
}
You could print it using Arrays.toString(). This seems the simplest to me.
System.out.println(Arrays.toString(persons));
System.out.println(Arrays.deepToString(persons)); // for nested arrays
You could print it the java 8 way (using streams and method reference).
Arrays.stream(persons).forEach(System.out::println);
There might be other ways as well. Hope this helps. :)
If you Directly print any object of Person It will the ClassName#HashCode to the Code.
in your case com.foo.Person#2f92e0f4 is getting printed . Where Person is a class to which object belongs and 2f92e0f4 is hashCode of the Object.
public class Person {
private String name;
public Person(String name){
this.name = name;
}
// getter/setter omitted
#override
public String toString(){
return name;
}
}
Now if you try to Use the object of Person then it will print the name
Class Test
{
public static void main(String... args){
Person obj = new Person("YourName");
System.out.println(obj.toString());
}
}
If you look at the Object class (Parent class of all classes in Java) the toString() method implementation is
public String toString() {
return getClass().getName() + "#" + Integer.toHexString(hashCode());
}
whenever you print any object in Java then toString() will be call. Now it's up to you if you override toString() then your method will call other Object class method call.
Using Lombok #Data annotation on class will provide getter, setter, toString and hashcode. Using Lombok is better as it handles boilerplate code.
For a "deep" toString() there is an alternative to the JSON based answers (Jackson, GSON, etc.): ReflectionToStringBuilder from the Apache Commons Lang 3 library, with RecursiveToStringStyle or MultilineRecursiveToStringStyle. Code example:
System.out.println("My object: " +
ReflectionToStringBuilder.toString(theObject, new RecursiveToStringStyle()));
Output examples:
// RecursiveToStringStyle
Person#7f54[name=Stephen,age=29,smoker=false,job=Job#43cd2[title=Manager]]
// MultilineRecursiveToStringStyle
Person#7f54[
name=Stephen,
age=29,
smoker=false,
job=Job#43cd2[
title=Manager
]
]
I managed to get this done using Jackson in Spring 5. Depending on the object it might not work in all cases.
import com.fasterxml.jackson.databind.ObjectMapper;
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(yourObject));
the output would look like
{
"id" : 1,
"fieldOne" : "string"
}
Here are more examples using Jackson
If you use GSON instead It might look like
Gson gson = new Gson();
System.out.println(gson.toJson(yourObject));
If you are using project Lombok you could use the #ToString annotation and generate a standard toString() method without adding boilerplate.
import lombok.ToString;
#ToString
public class LoginDto {
private String user;
private String pass;
}
...
System.out.println(loginDto.toString());
// LoginDto(user=x#xxx.x, pass=xxxxx)
I would like to convert a parameter and then call second method with this parameter.
The convention would be that there is always the same method overloaded with the specific type. The idea is to solve it with Spring AOP.
#Component
public class ExampleAspect {
#Around( "#annotation(Example)" )
public Object test( final ProceedingJoinPoint joinPoint ) throws Throwable {
final MethodSignature signature = (MethodSignature) joinPoint.getSignature();
final Method method = signature.getMethod();
final Example example = method.getAnnotation( Example.class );
final Object[] args = joinPoint.getArgs();
final String test = args[example.value()].toString();
final Bar bar = convertToBar(test)
args[example.value()] = bar;
//ReflectionUtils?
// call getBar(Bar bar)
//return joinPoint.proceed( args );
}
}
Here is the service
#Example(0)
public Object getBar(String test) {}
public Object getBar(Bar test) {}
Are there any better options or ideas?
EDIT:
Cannot inject the target bean, because this AOP should be used by more than specific target bean.
1 possible solution not sure if there is a smarter solution
#Around("#annotation(Example)")
public Object test(final ProceedingJoinPoint joinPoint) throws Throwable {
final MethodSignature signature = (MethodSignature) joinPoint.getSignature();
final Method method = signature.getMethod();
final Example example = method.getAnnotation(Example.class);
final Object[] args = joinPoint.getArgs();
final String bar = args[example.value()].toString();
final Bar aspectModelUrn = convertFromStringToBar(bar);
args[example.value()] = bar;
final Class<?>[] parameterTypes = method.getParameterTypes();
parameterTypes[example.value()] = Bar.class;
final Method newMethod = ReflectionUtils.findMethod(joinPoint.getTarget().getClass(), method.getName(), parameterTypes);
if (newMethod == null) {
throw new IllegalArgumentException("There is no method blubb. Have you forget to create the delegate method");
}
return newMethod.invoke(joinPoint.getTarget(), args);
}
Following code would provide a handle to the annotation and the target bean (for example , here TestComponent)
A call to the TestComponent.getBar() annotated with #Example would be intercepted and advised.
#Aspect
#Component
public class ExampleAspect {
#Around("#annotation(example) && target(bean)")
public Object test(final ProceedingJoinPoint joinPoint,Example example,TestComponent bean) throws Throwable {
String value = String.valueOf(example.value());
Bar bar = convertToBar(value);
bean.getBar(bar);
return joinPoint.proceed();
}
}
Do go through Spring AOP documentation : Passing Parameters to Advice for more details.
Note : For better performance it is a good idea to limit the scope of the expression as follows.
#Around("#annotation(example) && within(com.xyz.service..*) && target(bean)")
where com.xyz.service..* will limit the expression scope only to the beans with in the package com.xyz.service..* and its sub-packages.
I wrote this code.
#GetMapping("/test")
public Response search(#RequestParam String value) {
System.out.println(value);
return new Response(value)
}
Some body request like
/test?value=a&value=b&value=c
value binded a,b,c
I want always bind first parmeter. Take a, ignore b, c.
Is there way using #RequestParam?
Or have to use HttpServletRequest and parsing parameter?
In this case you can use #RequestParam List<String> value instead of #RequestParam String value, and get the first value value.get(0) ignore the rest of them
For Example
http://rentacar.com/api/v1/search?make=audi&model=A8&type=6&type=11&type=12&color=RED&color=GREY
Method
public List<Vehicle> search(
#RequestParam(value="make", required=false) String make,
#RequestParam(value="model", required=false) String model,
#RequestParam(value="type", required=false) List<String> types,
#RequestParam(value="color", required=false) List<String> colors)
{
....
}
Great question!
I wrote this code to find out how this works. I included it in the test packages.
#RunWith(SpringRunner.class)
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
#ActiveProfiles("test")
public class ControllerTest {
#LocalServerPort
private int port;
private URL url;
#Autowired
private TestRestTemplate template;
#Before
public void setUp() throws Exception {
this.url = new URL("http://localhost:" + port + "/test?value=a&value=b&value=c");
}
#Test
public void getHello() throws Exception {
ResponseEntity<String> response = template.getForEntity(url.toString(),
String.class);
Assert.assertEquals(HttpStatus.OK, response.getStatusCode());
Assert.assertEquals(response.getBody(), "a");
System.out.println("response = " + response);
}
}
I then modified your code to accept an array of strings, and only pass the first element to your Response Constructor.
Notice the changes in your code in the signature and return statement.
#GetMapping("/test")
public String search(#RequestParam String[] value) {
System.out.println(value);
return new Response(value[0]);
}
With your test, you can now explore using a List type for your request param and quickly see how the behaviour has changed.
I am using resteasy, and till now I am just sending and receiving string as parameters and every thing was OK, but now I want to send a complex object ( List<Map<String, ObjectVal>> ) as one of my parameters. My objectVal class has two simple field ( id and value, with getters and setters).
I can find different question and answers for sending objects as parameters but all of them are missing something and not useful for me.
here is my functions with a simple string parameter
#GET
#Path("/isUserAuthorizedToDocument")
public Response isUserAuthorizedToDocumentService(
#QueryParam("userID") String userID){
.............
.............
}
and the client
private ClientRequest req =new ClientRequest(....url with path and ....)
req.queryParameter("userID", user.getUserId());
ClientResponse<Boolean> response = req.get(Boolean.class);
Now I want to send a parameter from my client in the form of List<Map<String,ObjectVal>> and recieve it in my rest function.
My ObjectVal class
#XmlRootElement(name = "objectValueDTO")
public class ObjectValueDTO implements Serializable {
/**
* Id for this class
*/
private static final long serialVersionUID = 164186789404269392L;
// Id on object type
private String objectTypeID = "";
// Selection
private String value = "";
/** Getter and Setters */
#XmlElement
public String getObjectTypeID() {
return objectTypeID;
}
public void setObjectTypeID(String objectTypeID) {
this.objectTypeID = objectTypeID;
}
#XmlElement
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
any help will be appreciated
I may be niave on this. But when you have to send complex parameters, you need to use PUT and send the parameters in the request.
Whats the best way to save variables like userid that is stored and reachable from different pages in WP7.
There's the querystring method, but can be kind of a pain to implement.
When navigating, pass the parameter like a HTTP querystring.
Then, on the otherside, check if the key exists, and extract the value. The downside of this is if you need to do more than 1, you need to type it in yourself, and it only supports strings.
So to pass an integer, you'd need to convert it. (And to pass a complex object, you need to take all the pieces you need to recompile it on the other side)
NavigationService.Navigate(new Uri("/PanoramaPage1.xaml?selected=item2", UriKind.Relative));
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
string selected = String.Empty;
//check to see if the selected parameter was passed.
if (NavigationContext.QueryString.ContainsKey("selected"))
{
//get the selected parameter off the query string from MainPage.
selected = NavigationContext.QueryString["selected"];
}
//did the querystring indicate we should go to item2 instead of item1?
if (selected == "item2")
{
//item2 is the second item, but 0 indexed.
myPanorama.DefaultItem = myPanorama.Items[1];
}
base.OnNavigatedTo(e);
}
Here's a sample app that uses a querystring.
http://dl.dropbox.com/u/129101/Panorama_querystring.zip
A easier (and better) idea is to define a variable globally, or use a static class. In App.xaml.cs, define
using System.Collections.Generic;
public static Dictionary<string,object> PageContext = new Dictionary<string,object>;
Then, on the first page, simply do
MyComplexObject obj;
int four = 4;
...
App.PageContext.Add("mycomplexobj",obj);
App.PageContext.Add("four",four);
Then, on the new page, simply do
MyComplexObj obj = App.PageContext["mycomplexobj"] as MyComplexObj;
int four = (int)App.PageContext["four"];
To be safe, you should probably check if the object exists:
if (App.PageContext.ContainsKey("four"))
int four = (int)App.PageContext["four"];
You may use an App level variable (defined in App.xaml.cs) and access it from anywhere within your app. If you want to persist, shove it into Isolated Storage and read it on App launch/activate. There are helpers available to JSon serialize/deserialize your reads/writes from the Isolated Storage.
Check out Jeff's post (here) on tips to use Isolated Storage.
Hope this helps!
Well "best" is always subjective, however, I think an application service is a good candidate for this sort of thing:-
public interface IPhoneApplicationService : IApplicationService
{
string Name {get; set;}
object Deactivating();
void Activating(object state);
}
public class AuthenticationService : IPhoneApplicationService
{
public static AuthenticationService Current {get; private set; }
public void StartService(ApplicationServiceContext context)
{
Current = this;
}
public void StopService()
{
Current = null;
}
public string Name {get; set;}
public object Deactivating()
{
// Return an serialisable object such as a Dictionary if necessary.
return UserID;
}
public void Activating(object state)
{
UserID = (int)state;
}
public int UserID { get; private set; }
public void Logon(string username, string password)
{
// Code here that eventually assigns to UserID.
}
}
You place an instance of this in your App.xaml:-
<Application.ApplicationLifetimeObjects>
<!--Required object that handles lifetime events for the application-->
<shell:PhoneApplicationService
Launching="Application_Launching" Closing="Application_Closing"
Activated="Application_Activated" Deactivated="Application_Deactivated"/>
<local:AuthenticationService Name="AuthServ" />
</Application.ApplicationLifetimeObjects>
Now you do need to tweak the App.xaml.cs:-
private void Application_Activated(object sender, ActivatedEventArgs e)
{
var state = PhoneApplicationService.Current.State;
foreach (var service in ApplicationLifetimeObjects.OfType<IPhoneApplicationService>())
{
if (state.ContainsKey(service.Name))
{
service.Activating(state[service.Name]);
}
}
}
private void Application_Deactivated(object sender, DeactivatedEventArgs e)
{
var state = PhoneApplicationService.Current.State;
foreach (var service in ApplicationLifetimeObjects.OfType<IPhoneApplicationService>())
{
if (state.ContainsKey(service.Name))
{
state[service.Name] = service.Deactivating();
}
else
{
state.Add(service.Name, service.Deactivating());
}
}
}
You can now access you UserID anywhere in your app with:-
AuthenticationService.Current.UserID
This general pattern can be used to maintain seperation of key application wide services (you don't load a whole bunch of incohesive properties into your App class). It also provides the hooks for maintaining state between activations which is essential.