[wpimath] Split WPIMathJNI into logical chunks (#5552)

This makes things easier to find, and speeds up compilation.

wpimath/src/main/native/cpp/jni/WPIMathJNI_Exceptions.cpp

@@ -0,0 +1,56 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "WPIMathJNI_Exceptions.h"
+
+#include <jni.h>
+
+using namespace wpi::java;
+
+//
+// Globals and load/unload
+//
+
+JException illegalArgEx;
+JException ioEx;
+JException trajectorySerializationEx;
+
+static const JExceptionInit exceptions[] = {
+    {"java/lang/IllegalArgumentException", &illegalArgEx},
+    {"java/io/IOException", &ioEx},
+    {"edu/wpi/first/math/trajectory/"
+     "TrajectoryUtil$TrajectorySerializationException",
+     &trajectorySerializationEx}};
+
+extern "C" {
+
+JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void* reserved) {
+  JNIEnv* env;
+  if (vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6) != JNI_OK) {
+    return JNI_ERR;
+  }
+
+  // Cache references to exceptions
+  for (auto& c : exceptions) {
+    *c.cls = JException(env, c.name);
+    if (!*c.cls) {
+      return JNI_ERR;
+    }
+  }
+
+  return JNI_VERSION_1_6;
+}
+
+JNIEXPORT void JNICALL JNI_OnUnload(JavaVM* vm, void* reserved) {
+  JNIEnv* env;
+  if (vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6) != JNI_OK) {
+    return;
+  }
+  // Delete global references
+  for (auto& c : exceptions) {
+    c.cls->free(env);
+  }
+}
+
+}  // extern "C"