Code drop from //branches/cupcake/...@124589

samples/PlatformLibrary/jni/Android.mk

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+#
+# Copyright (C) 2008 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# This makefile supplies the rules for building a library of JNI code for
+# use by our example platform shared library.
+
+LOCAL_PATH:= $(call my-dir)
+include $(CLEAR_VARS)
+
+LOCAL_MODULE_TAGS := samples
+
+# This is the target being built.
+LOCAL_MODULE:= libplatform_library_jni
+
+# All of the source files that we will compile.
+LOCAL_SRC_FILES:= \
+	PlatformLibrary.cpp
+
+# All of the shared libraries we link against.
+LOCAL_SHARED_LIBRARIES := \
+	libandroid_runtime \
+	libnativehelper \
+	libcutils \
+	libutils
+
+# No static libraries.
+LOCAL_STATIC_LIBRARIES :=
+
+# Also need the JNI headers.
+LOCAL_C_INCLUDES += \
+	$(JNI_H_INCLUDE)
+
+# No specia compiler flags.
+LOCAL_CFLAGS +=
+
+# Don't prelink this library.  For more efficient code, you may want
+# to add this library to the prelink map and set this to true.
+LOCAL_PRELINK_MODULE := false
+
+include $(BUILD_SHARED_LIBRARY)

samples/PlatformLibrary/jni/PlatformLibrary.cpp

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+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "PlatformLibrary"
+#include "utils/Log.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <assert.h>
+
+#include "jni.h"
+
+
+// ----------------------------------------------------------------------------
+
+/*
+ * Field/method IDs and class object references.
+ *
+ * You should not need to store the JNIEnv pointer in here.  It is
+ * thread-specific and will be passed back in on every call.
+ */
+static struct {
+    jclass      platformLibraryClass;
+    jfieldID    jniInt;
+    jmethodID   yodel;
+} gCachedState;
+
+// ----------------------------------------------------------------------------
+
+/*
+ * Helper function to throw an arbitrary exception.
+ *
+ * Takes the exception class name, a format string, and one optional integer
+ * argument (useful for including an error code, perhaps from errno).
+ */
+static void throwException(JNIEnv* env, const char* ex, const char* fmt,
+    int data) {
+
+    if (jclass cls = env->FindClass(ex)) {
+        if (fmt != NULL) {
+            char msg[1000];
+            snprintf(msg, sizeof(msg), fmt, data);
+            env->ThrowNew(cls, msg);
+        } else {
+            env->ThrowNew(cls, NULL);
+        }
+
+        /*
+         * This is usually not necessary -- local references are released
+         * automatically when the native code returns to the VM.  It's
+         * required if the code doesn't actually return, e.g. it's sitting
+         * in a native event loop.
+         */
+        env->DeleteLocalRef(cls);
+    }
+}
+
+/*
+ * Trivial sample method.
+ *
+ * If "bad" is true, this throws an exception.  Otherwise, this sets the
+ * "mJniInt" field to 42 and returns 24.
+ */
+static jint PlatformLibrary_getJniInt(JNIEnv* env, jobject thiz, jboolean bad) {
+    if (bad) {
+        throwException(env, "java/lang/IllegalStateException",
+                "you are bad", 0);
+        return 0;       /* return value will be ignored */
+    }
+    env->SetIntField(thiz, gCachedState.jniInt, 42);
+    return (jint)24;
+}
+
+/*
+ * A more complex sample method.
+ *
+ * This takes a String as an argument, and returns a new String with
+ * characters in reverse order.  The new string is passed to another method.
+ * This demonstrates basic String manipulation functions and method
+ * invocation.
+ *
+ * This method is declared "static", so there's no "this" pointer; instead,
+ * we get a pointer to the class object.
+ */
+static jstring PlatformLibrary_reverseString(JNIEnv* env, jclass clazz,
+    jstring str) {
+
+    if (str == NULL) {
+        throwException(env, "java/lang/NullPointerException", NULL, 0);
+        return NULL;
+    }
+
+    /*
+     * Get a pointer to the string's UTF-16 character data.  The data
+     * may be a copy or a pointer to the original.  Since String data
+     * is immutable, we're not allowed to touch it.
+     */
+    const jchar* strChars = env->GetStringChars(str, NULL);
+    if (strChars == NULL) {
+        /* something went wrong */
+        LOGW("Couldn't get string chars\n");
+        return NULL;
+    }
+    jsize strLength = env->GetStringLength(str);
+
+    /*
+     * Write a progress message to the log.  Log messages are UTF-8, so
+     * we want to convert the string to show it.
+     */
+    const char* printable = env->GetStringUTFChars(str, NULL);
+    if (printable != NULL) {
+        LOGD("Reversing string '%s'\n", printable);
+        env->ReleaseStringUTFChars(str, printable);
+    }
+
+    /*
+     * Copy the characters to temporary storage, reversing as we go.
+     */
+    jchar tempChars[strLength];
+    for (int i = 0; i < strLength; i++) {
+        tempChars[i] = strChars[strLength -1 -i];
+    }
+
+    /*
+     * Release the original String.  That way, if something fails later on,
+     * we don't have to worry about this leading to a memory leak.
+     */
+    env->ReleaseStringChars(str, strChars);
+    strChars = NULL;            /* this pointer no longer valid */
+
+    /*
+     * Create a new String with the chars.
+     */
+    jstring result = env->NewString(tempChars, strLength);
+    if (result == NULL) {
+        LOGE("NewString failed\n");
+        return NULL;
+    }
+
+    /*
+     * Now let's do something with it.  We already have the methodID for
+     * "yodel", so we can invoke it directly.  It's in our class, so we
+     * can use the Class object reference that was passed in.
+     */
+    env->CallStaticVoidMethod(clazz, gCachedState.yodel, result);
+
+    return result;
+}
+
+
+// ----------------------------------------------------------------------------
+
+/*
+ * Array of methods.
+ *
+ * Each entry has three fields: the name of the method, the method
+ * signature, and a pointer to the native implementation.
+ */
+static const JNINativeMethod gMethods[] = {
+    { "getJniInt",          "(Z)I",
+                        (void*)PlatformLibrary_getJniInt },
+    { "reverseString",      "(Ljava/lang/String;)Ljava/lang/String;",
+                        (void*)PlatformLibrary_reverseString },
+};
+
+/*
+ * Do some (slow-ish) lookups now and save the results.
+ *
+ * Returns 0 on success.
+ */
+static int cacheIds(JNIEnv* env, jclass clazz) {
+    /*
+     * Save the class in case we want to use it later.  Because this is a
+     * reference to the Class object, we need to convert it to a JNI global
+     * reference.
+     */
+    gCachedState.platformLibraryClass = (jclass) env->NewGlobalRef(clazz);
+    if (clazz == NULL) {
+        LOGE("Can't create new global ref\n");
+        return -1;
+    }
+
+    /*
+     * Cache field and method IDs.  IDs are not references, which means we
+     * don't need to call NewGlobalRef on them.
+     */
+    gCachedState.jniInt = env->GetFieldID(clazz, "mJniInt", "I");
+    if (gCachedState.jniInt == NULL) {
+        LOGE("Can't find PlatformLibrary.mJniInt\n");
+        return -1;
+    }
+
+    gCachedState.yodel = env->GetStaticMethodID(clazz, "yodel",
+        "(Ljava/lang/String;)V");
+    if (gCachedState.yodel == NULL) {
+        LOGE("Can't find PlatformLibrary.yodel\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+/*
+ * Explicitly register all methods for our class.
+ *
+ * While we're at it, cache some class references and method/field IDs.
+ *
+ * Returns 0 on success.
+ */
+static int registerMethods(JNIEnv* env) {
+    static const char* const kClassName =
+        "com/example/android/platform_library/PlatformLibrary";
+    jclass clazz;
+
+    /* look up the class */
+    clazz = env->FindClass(kClassName);
+    if (clazz == NULL) {
+        LOGE("Can't find class %s\n", kClassName);
+        return -1;
+    }
+
+    /* register all the methods */
+    if (env->RegisterNatives(clazz, gMethods,
+            sizeof(gMethods) / sizeof(gMethods[0])) != JNI_OK)
+    {
+        LOGE("Failed registering methods for %s\n", kClassName);
+        return -1;
+    }
+
+    /* fill out the rest of the ID cache */
+    return cacheIds(env, clazz);
+}
+
+// ----------------------------------------------------------------------------
+
+/*
+ * This is called by the VM when the shared library is first loaded.
+ */
+jint JNI_OnLoad(JavaVM* vm, void* reserved) {
+    JNIEnv* env = NULL;
+    jint result = -1;
+
+    if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
+        LOGE("ERROR: GetEnv failed\n");
+        goto bail;
+    }
+    assert(env != NULL);
+
+    if (registerMethods(env) != 0) {
+        LOGE("ERROR: PlatformLibrary native registration failed\n");
+        goto bail;
+    }
+
+    /* success -- return valid version number */
+    result = JNI_VERSION_1_4;
+
+bail:
+    return result;
+}