Class Throwable
The Throwable class is the superclass of all errors and exceptions in the Java language. Only objects that are instances of this class (or one of its subclasses) are thrown by the Java Virtual Machine or can be thrown by the Java throw statement. Similarly, only this class or one of its subclasses can be the argument type in a catch clause. For the purposes of compile-time checking of exceptions, Throwable and any subclass of Throwable that is not also a subclass of either RuntimeException or Error are regarded as checked exceptions.
Instances of two subclasses, Error and Exception , are conventionally used to indicate that exceptional situations have occurred. Typically, these instances are freshly created in the context of the exceptional situation so as to include relevant information (such as stack trace data).
A throwable contains a snapshot of the execution stack of its thread at the time it was created. It can also contain a message string that gives more information about the error. Over time, a throwable can suppress other throwables from being propagated. Finally, the throwable can also contain a cause: another throwable that caused this throwable to be constructed. The recording of this causal information is referred to as the chained exception facility, as the cause can, itself, have a cause, and so on, leading to a «chain» of exceptions, each caused by another.
One reason that a throwable may have a cause is that the class that throws it is built atop a lower layered abstraction, and an operation on the upper layer fails due to a failure in the lower layer. It would be bad design to let the throwable thrown by the lower layer propagate outward, as it is generally unrelated to the abstraction provided by the upper layer. Further, doing so would tie the API of the upper layer to the details of its implementation, assuming the lower layer’s exception was a checked exception. Throwing a «wrapped exception» (i.e., an exception containing a cause) allows the upper layer to communicate the details of the failure to its caller without incurring either of these shortcomings. It preserves the flexibility to change the implementation of the upper layer without changing its API (in particular, the set of exceptions thrown by its methods).
A second reason that a throwable may have a cause is that the method that throws it must conform to a general-purpose interface that does not permit the method to throw the cause directly. For example, suppose a persistent collection conforms to the Collection interface, and that its persistence is implemented atop java.io . Suppose the internals of the add method can throw an IOException . The implementation can communicate the details of the IOException to its caller while conforming to the Collection interface by wrapping the IOException in an appropriate unchecked exception. (The specification for the persistent collection should indicate that it is capable of throwing such exceptions.)
A cause can be associated with a throwable in two ways: via a constructor that takes the cause as an argument, or via the initCause(Throwable) method. New throwable classes that wish to allow causes to be associated with them should provide constructors that take a cause and delegate (perhaps indirectly) to one of the Throwable constructors that takes a cause. Because the initCause method is public, it allows a cause to be associated with any throwable, even a «legacy throwable» whose implementation predates the addition of the exception chaining mechanism to Throwable .
By convention, class Throwable and its subclasses have two constructors, one that takes no arguments and one that takes a String argument that can be used to produce a detail message. Further, those subclasses that might likely have a cause associated with them should have two more constructors, one that takes a Throwable (the cause), and one that takes a String (the detail message) and a Throwable (the cause).
Java set the message of an exception
Solution 1: You can create you own Custom Exception and when runtime exception catch you can throw your custom exception with proper message. Exception messages should not need to be changed.
Changing exception cause message before throwing?
You can create you own Custom Exception and when runtime exception catch you can throw your custom exception with proper message.
public class MyException extends Exception < public MyException(String message) < super(message); >> catch (RuntimeException ex) < //here i can get message using ex.getMessage(); throw new RuntimeException("bla bla"); >If you want to keep info about original location of the first exception use this:
catch (RuntimeException ex) < //here i can get message using ex.getMessage(); throw new RuntimeException("bla bla", ex); >Yes , It is possible. Throw a new RuntimeException passing your custom message.
Use the constructor public RuntimeException(String message, Throwable cause)
Constructs a new runtime exception with the specified detail message and cause.
catch (RuntimeException ex)
How to print custom message instead of, When an exception occurred the program gets terminated abruptly and, the code past the line that generated the exception never gets executed. Printing the Exception message. You can print the exception message in Java using one of the following methods which are inherited from Throwable class.
How to add message to response with exception
Your method could instead or returning void return class ResponseEntity . See an article on how to use it: Using Spring ResponseEntity to Manipulate the HTTP Response. Another way to provide detailed error message is to write a class annotated with @ControllerAdvice . See some info on that (and other stuff) here: building rest services with spring
How to get an exception message in a String variable in, your catch (Exception e) block will catch all exceptions (other than SQLException which you are specifically catching above). Some exceptions e.g. NullPointerException can have null details message …
Get the message of a java throwable in a string
From the docs of the Throwable class (Where getMessage() comes from):
Returns: the detail message string of this Throwable instance ( which may be null ).
Thus a null message is a perfectly legal response from getMessage() and is created whenever the Exception class is instantiated with no arguments.
If by message, you mean the Stack Trace , then Throwable defines a getStackTrace method, which allows you to iterate through the various elements that would be printed in a printStackTrace , from which you can get their string output just using toString()
You could do something like this:
Did you try to use e.toString() ?
Custom Exception message with new line in Java, Custom Exception message with new line in Java. Ask Question Asked 5 years, 1 month ago. If I add
. don’t pass an entire exception. Pass only the messages you want the user to see in …
How to store exception messages
I will chime in with what @MikeNakis says: the exception type used should be fine-grained enough that you can discern to some reasonable degree what the problem was from looking only at that and possibly the stack trace. If the intent was that one should just throw Exception s around, then that type would have been made final , sealed or whatever happens to be the term in one’s programming language of choice, but that is not the case in any language or framework I know of. In fact, catching Exception is often frowned upon, as it is a cop-out that is very likely to hide real, serious problems.
The exception message should be used to provide details that cannot reasonably be expressed through the type system.
Your second example is actually worse, IMO: you are replacing hard-and-fast types with string literals that are bound to become out of date, misused, changed in ways not expected in some parts of the code, or in any number of other possible ways inaccurate. And in ways that the compiler doesn’t have a glimmer of hope of helping you catch, in any language.
Exception messages should not need to be changed. To the extent that they are to be used at all (which should be sparingly, IMO; see previous discussion), they should be meant for programmers (and possibly power users, who can enable display of the messages through some mechanism), not end users. Thus, the exact phrasing becomes less important than the fact that the message clearly describes the conditions that caused the exception but which cannot be adequately expressed through the type system.
Also, unless you really need free-form text messages with no built-in semantics as exception clarifiers (unlikely), you are almost always better off forgetting entirely about building and passing a single string message. Let’s say you have a piece of code that requires that a certain variable is within a given range, and must throw an exception otherwise. Instead of (pseudo-C#/.NET; I know you could use string building features like StringBuilder or String.Format , but that’s not the point here):
if (x < 3 || x >10) throw new VeryGeneralException("Got " + x.ToString() + " wanted min 3 max 10"); you might do something like:
public class OutOfRangeException : Exception < public int Value < get; private set; >public int MinValue < get; private set; >public int MaxValue < get; private set; >public OutOfRangeException(int value, int minvalue, int maxvalue) < base("Got " + value.ToString() + " wanted min " + minvalue.ToString() + " max " + maxvalue.ToString()); this.Value = value; this.MinValue = minvalue; this.MaxValue = maxvalue; >> . then far later . if (x < 3 || x >10) throw new OutOfRangeException(value: x, minvalue: 3, maxvalue: 10); - by looking at only the exception type name, you know that some value was out of its allowed range
- with the resulting generated message, you know the value of the variable in question and its expected range
- along with the full stack trace, you have a pretty decent idea how you got to that point (which, depending on the architecture and the semantics of the value in question, may or may not help you determine why the value was out of its allowed range)
This way, a single exception, including its stack trace, gives you about as much detail as you can hope to get short of a step-by-step description of how to repeat the error.
In my opinion the constructor of Exception should not be accepting a string message parameter, nor any other kind of identifier that stands for the message. The message is the name of the type of the exception .
In my projects for convenience I make use of an exception that I call GenericException which accepts a string message, but the intent is to replace it with a specific exception type, created especially for that purpose, before deployment, ideally before source code commit.
What you can do is have a dictionary in which the key is an exception type and the value is the corresponding message. You can also use formatting in the message, and use reflection to fetch values of members of the exception, and pass them to the String.Format function, so as to make your messages richer.
So, in your case you should define a ConditionNotMetException , derived from System.Exception . If you have no other information to pass in it, then leave it as an empty class. Alternatively, you may want to include some members in it, containing additional information about the condition which was not met, why it was not met, etc.
However, these members should be just raw values, they should not be processed into string messages by the exception. For example, if you had an exception called DateOutOfRangeException you may want to include in it 3 DateTime fields: one for the date that was found to be out of range, and another two defining the range. Then, it is the responsibility of the application to present the user with a meaningful message containing these three dates.
Let the message be telling. A good thing to tell is what went wrong:
if(!Condition1) throw new Exception(«!Condition1»);
if(!Condition2) throw new Exception(«!Condition2»);
The more complex the expression in the if the more information you will need to avoid a debug step. For instance
This will allow the maintenance engineer to analyze the error without having to run the program again. Some day you will appreciate this
Different Ways to Print Exception Messages in Java, Methods to Print Exceptions in Java. There are three methods to print exception messages in Java. These are: 1. java.lang.Throwable.printStackTrace() method: By using this method, we will get the name(e.g., java.lang.ArithmeticException) and description(e.g., / by zero) of an exception …