| Maven resolve |
[ERROR] Failed to execute goal on project x: Could not resolve dependencies for project |
Maven couldn’t download or find one or more dependencies. |
| release version not supported |
[ERROR] Fatal error compiling: error: release version 17 not supported |
The JDK running Maven is older than the Java version the project compiles for. |
| InvalidDefinitionException |
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class X and no properties discovered |
Jackson can’t serialize the class — it has no public getters/fields, or it’s a Hibernate proxy, or Java 8 dat… |
| MismatchedInputException |
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList` from Object value |
Jackson found JSON whose shape doesn’t match the target Java type (object vs array, string vs number, missing… |
| UnrecognizedPropertyException |
com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "x", not marked as ignorable |
The JSON contains a field your Java class doesn’t have, and Jackson is configured to fail on unknown properti… |
| Communications link failure |
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure |
The MySQL JDBC driver couldn’t reach the database (or the connection dropped). |
| Gradle wrapper main class |
Error: Could not find or load main class org.gradle.wrapper.GradleWrapperMain |
The Gradle wrapper JAR (gradle/wrapper/gradle-wrapper.jar) is missing or corrupt. |
| JAVA_HOME not set |
ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. |
Build tools (Gradle, Maven, Android tools) can’t find a JDK. |
| DataSource url not specified |
Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured. |
Spring Boot found JDBC/JPA on the classpath but no database URL. |
| HikariCP timeout |
HikariPool-1 - Connection is not available, request timed out after 30000ms |
The connection pool was exhausted — all connections were busy for 30 seconds. |
| HttpMessageNotReadableException |
HttpMessageNotReadableException: JSON parse error / Required request body is missing |
Spring couldn’t read the request body into your @RequestBody object. |
| NonUniqueResultException |
IncorrectResultSizeDataAccessException: query did not return a unique result: 2 |
A query expected one row but found several. |
| FileNotFoundException |
java.io.FileNotFoundException: config.properties (No such file or directory) |
Java couldn’t open the file — wrong path relative to the working directory, missing file, or a classpath reso… |
| Stream closed |
java.io.IOException: Stream closed |
Code read or wrote a stream after it was closed — often by a try-with-resources block or a wrapper closing th… |
| ArithmeticException |
java.lang.ArithmeticException: / by zero |
Integer division or modulo by zero. |
| ArrayIndexOutOfBoundsException |
java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5 |
Code accessed an array index outside 0 … length-1. |
| ClassCastException |
java.lang.ClassCastException: class A cannot be cast to class B |
An object was cast to a type it isn’t. |
| ClassNotFoundException |
java.lang.ClassNotFoundException / NoClassDefFoundError |
The JVM couldn’t find a class on the classpath at runtime. |
| ExceptionInInitializerError |
java.lang.ExceptionInInitializerError |
A static initializer (static block or static field) threw an exception while the class was loading. |
| IllegalArgumentException |
java.lang.IllegalArgumentException |
A method rejected an argument value as invalid. |
| IllegalStateException |
java.lang.IllegalStateException |
A method was called when the object wasn’t in the right state for it. |
| InterruptedException |
java.lang.InterruptedException (sleep interrupted) |
A blocked thread (sleep, wait, join, queue take) was interrupted by another thread. |
| NoSuchMethodError |
java.lang.NoSuchMethodError |
Code compiled against one version of a library is running with another version where the method doesn’t exist. |
| NullPointerException |
java.lang.NullPointerException |
Code called a method or accessed a field on a reference that is `null`. |
| NumberFormatException |
java.lang.NumberFormatException: For input string: "x" |
A string couldn’t be parsed as a number — it’s empty, has spaces/commas, is too large, or isn’t numeric. |
| OutOfMemoryError |
java.lang.OutOfMemoryError: Java heap space |
The JVM ran out of heap memory and garbage collection couldn’t free enough. |
| StackOverflowError |
java.lang.StackOverflowError |
The thread’s call stack overflowed — almost always unbounded recursion, sometimes a bidirectional toString/eq… |
| StringIndexOutOfBoundsException |
java.lang.StringIndexOutOfBoundsException: begin 0, end 10, length 5 |
substring()/charAt() used an index outside the string. |
| UnsupportedClassVersionError |
java.lang.UnsupportedClassVersionError: class file version 61.0, this version of the Java Runtime only recognizes up to 55.0 |
Code compiled for a newer Java version is running on an older JVM. |
| UnsupportedOperationException |
java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable) |
Code tried to modify an immutable or fixed-size collection. |
| ConnectException |
java.net.ConnectException: Connection refused |
Nothing is listening at the host:port the Java client connected to. |
| SocketException reset |
java.net.SocketException: Connection reset |
The remote side closed the TCP connection abruptly while Java was reading or writing. |
| UnknownHostException |
java.net.UnknownHostException: api.example.com |
DNS resolution failed for the hostname. |
| AccessDeniedException |
java.nio.file.AccessDeniedException: /path |
The OS denied a file operation to the Java process. |
| NoSuchFileException |
java.nio.file.NoSuchFileException: /path/file |
An NIO Files operation targeted a path that doesn’t exist. |
| Unparseable date |
java.text.ParseException: Unparseable date: "x" |
SimpleDateFormat couldn’t parse the string with its pattern. |
| DateTimeParseException |
java.time.format.DateTimeParseException: Text '31/12/2024' could not be parsed at index 2 |
A java.time parse call got text that doesn’t match the expected format. |
| TimeoutException |
java.util.concurrent.TimeoutException |
A Future.get(timeout) or async operation didn’t complete in the allowed time. |
| ConcurrentModificationException |
java.util.ConcurrentModificationException |
A collection was modified while being iterated (even in a single thread). |
| InputMismatchException |
java.util.InputMismatchException (Scanner) |
Scanner.nextInt()/nextDouble() read a token that isn’t that type. |
| NoSuchElementException |
java.util.NoSuchElementException: No value present |
Code asked for an element that doesn’t exist — Optional.get() on empty, iterator.next() past the end, Scanner… |
| PKIX path building failed |
javax.net.ssl.SSLHandshakeException: PKIX path building failed: unable to find valid certification path to requested target |
Java doesn’t trust the server’s certificate chain (self-signed, corporate proxy CA, or missing intermediate). |
| MethodArgumentNotValidException |
MethodArgumentNotValidException: Validation failed for argument [0] |
Bean Validation (@Valid with @NotNull, @Email, @Size…) rejected the request body. |
| Hibernate ConstraintViolationException |
org.hibernate.exception.ConstraintViolationException: could not execute statement |
The database rejected an insert/update because of a constraint (unique, foreign key, not null). |
| LazyInitializationException |
org.hibernate.LazyInitializationException: could not initialize proxy - no Session |
A lazy-loaded association was accessed after the Hibernate session/transaction closed. |
| TransientObjectException |
org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing |
An entity references another entity that hasn’t been saved yet, and no cascade is configured. |
| circular references |
The dependencies of some of the beans in the application context form a cycle |
Two or more Spring beans depend on each other through constructors, and Spring Boot 2.6+ forbids cycles by de… |
| UnsatisfiedDependencyException |
UnsatisfiedDependencyException / NoSuchBeanDefinitionException: No qualifying bean of type 'X' available |
Spring couldn’t find (or choose) a bean to inject. |
| Port 8080 in use |
Web server failed to start. Port 8080 was already in use. |
Spring Boot couldn’t bind its embedded server port because another process uses it. |
| Whitelabel Error Page |
Whitelabel Error Page — This application has no explicit mapping for /error |
Spring Boot’s default error page — the request hit no controller mapping (404) or a controller threw (500). |