JNI: Add calls to get field IDs

Task-number: QTBUG-92952
Change-Id: Ie68ede4b00a411064a29925b28b1f60a84d2d678
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>

src/corelib/kernel/qjnienvironment.cpp

@@ -255,6 +255,51 @@ jmethodID QJniEnvironment::findStaticMethod(jclass clazz, const char *methodName
     return id;
 }
 
+
+/*!
+    Searches for an member field of a class \a clazz. The field is specified
+    by its \a fieldName and \a signature.
+
+    Returns the field ID or \c nullptr if the field is not found.
+
+    A usecase for this method is searching for class fields and caching their
+    IDs, so that they could later be used for getting/setting the fields.
+
+    \since 6.2
+*/
+jfieldID QJniEnvironment::findField(jclass clazz, const char *fieldName, const char *signature)
+{
+    if (clazz) {
+        jfieldID id = d->jniEnv->GetFieldID(clazz, fieldName, signature);
+        if (!checkAndClearExceptions())
+            return id;
+    }
+
+    return nullptr;
+}
+
+/*!
+    Searches for a static field of a class \a clazz. The field is specified
+    by its \a fieldName and \a signature.
+
+    Returns the field ID or \c nullptr if the field is not found.
+
+    A usecase for this method is searching for class fields and caching their
+    IDs, so that they could later be used for getting/setting the fields.
+
+    \since 6.2
+*/
+jfieldID QJniEnvironment::findStaticField(jclass clazz, const char *fieldName, const char *signature)
+{
+    if (clazz) {
+        jfieldID id = d->jniEnv->GetStaticFieldID(clazz, fieldName, signature);
+        if (!checkAndClearExceptions())
+            return id;
+    }
+
+    return nullptr;
+}
+
 /*!
     \fn JavaVM *QJniEnvironment::javaVM()
 

src/corelib/kernel/qjnienvironment.h

@@ -61,6 +61,8 @@ public:
     jclass findClass(const char *className);
     jmethodID findMethod(jclass clazz, const char *methodName, const char *signature);
     jmethodID findStaticMethod(jclass clazz, const char *methodName, const char *signature);
+    jfieldID findField(jclass clazz, const char *fieldName, const char *signature);
+    jfieldID findStaticField(jclass clazz, const char *fieldName, const char *signature);
     static JavaVM *javaVM();
     bool registerNativeMethods(const char *className, const JNINativeMethod methods[], int size);
     bool registerNativeMethods(jclass clazz, const JNINativeMethod methods[], int size);

tests/auto/corelib/kernel/qjnienvironment/testdata/src/org/qtproject/qt/android/testdata/QtJniEnvironmentTestClass.java

@@ -33,6 +33,11 @@ public class QtJniEnvironmentTestClass
     private static native void callbackFromJava(String message);
     private static native void intCallbackFromJava(int value);
 
+    public final int INT_FIELD = 123;
+    public static final int S_INT_FIELD = 321;
+
+    QtJniEnvironmentTestClass() {}
+
     public static void appendJavaToString(String message)
     {
         callbackFromJava("From Java: " + message);

tests/auto/corelib/kernel/qjnienvironment/tst_qjnienvironment.cpp

@@ -49,6 +49,8 @@ private slots:
     void registerNativeMethodsByJclass();
     void findMethod();
     void findStaticMethod();
+    void findField();
+    void findStaticField();
 };
 
 void tst_QJniEnvironment::jniEnv()
@@ -203,6 +205,52 @@ void tst_QJniEnvironment::findStaticMethod()
     QVERIFY(!env.checkAndClearExceptions());
 }
 
+void tst_QJniEnvironment::findField()
+{
+    QJniEnvironment env;
+    jclass clazz = env.findClass(javaTestClass);
+    QVERIFY(clazz != nullptr);
+
+    // valid field
+    jfieldID validId = env.findField(clazz, "INT_FIELD", "I");
+    QVERIFY(validId != nullptr);
+
+    jmethodID constructorId = env.findMethod(clazz, "<init>", "()V");
+    QVERIFY(constructorId != nullptr);
+    jobject obj = env->NewObject(clazz, constructorId);
+    QVERIFY(!env.checkAndClearExceptions());
+    int value = env->GetIntField(obj, validId);
+    QVERIFY(!env.checkAndClearExceptions());
+    QVERIFY(value == 123);
+
+    // invalid signature
+    jfieldID invalidId = env.findField(clazz, "unknown", "I");
+    QVERIFY(invalidId == nullptr);
+    // check that all exceptions are already cleared
+    QVERIFY(!env.checkAndClearExceptions());
+}
+
+void tst_QJniEnvironment::findStaticField()
+{
+    QJniEnvironment env;
+    jclass clazz = env.findClass(javaTestClass);
+    QVERIFY(clazz != nullptr);
+
+    // valid field
+    jfieldID validId = env.findStaticField(clazz, "S_INT_FIELD", "I");
+    QVERIFY(validId != nullptr);
+
+    int size = env->GetStaticIntField(clazz, validId);
+    QVERIFY(!env.checkAndClearExceptions());
+    QVERIFY(size == 321);
+
+    // invalid signature
+    jfieldID invalidId = env.findStaticField(clazz, "unknown", "I");
+    QVERIFY(invalidId == nullptr);
+    // check that all exceptions are already cleared
+    QVERIFY(!env.checkAndClearExceptions());
+}
+
 QTEST_MAIN(tst_QJniEnvironment)
 
 #include "tst_qjnienvironment.moc"