1 # This file is part of NIT ( http://www.nitlanguage.org ).
3 # Licensed under the Apache License, Version 2.0 (the "License");
4 # you may not use this file except in compliance with the License.
5 # You may obtain a copy of the License at
7 # http://www.apache.org/licenses/LICENSE-2.0
9 # Unless required by applicable law or agreed to in writing, software
10 # distributed under the License is distributed on an "AS IS" BASIS,
11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 # See the License for the specific language governing permissions and
13 # limitations under the License.
15 # Supporting services for the FFI with Java
17 # This modules relies on `Sys::jvm`, `Sys::jni_env` and
18 # `Sys::create_default_jvm` to get a handle on a JVM. You can adapt the
19 # behavior of the FFI and services in this module by redefing
20 # `Sys::create_default_jvm` and supply your own JVM object. You can manage
21 # multiple java thread by switching the current environment in a redef
22 # of `Sys::jni_env`, and multiple JVM using `Sys::jvm`.
24 cflags
"-I $(JAVA_HOME)/include/ -I $(JAVA_HOME)/include/linux/"
25 ldflags
"-L $(JNI_LIB_PATH) -ljvm"
26 new_annotation extra_java_files
32 private var jvm_cache
: nullable JavaVM = null
33 private var jni_env_cache
: nullable JniEnv = null
35 # Default Java Virtual Machine to use (will be instantiated using
36 # `create_default_jvm` if not already set)
39 if jvm_cache
== null then create_default_jvm
40 return jvm_cache
.as(not null)
43 # Sets the current default Java Virtual Machine (use with `jni_env=`)
44 fun jvm
=(jvm
: JavaVM) do jvm_cache
= jvm
46 # Current main `JniEnv`
49 if jni_env_cache
== null then create_default_jvm
50 return jni_env_cache
.as(not null)
53 # Sets the current default JNI env (use with `jvm=`)
54 fun jni_env
=(jni_env
: JniEnv) do jni_env_cache
= jni_env
56 # Called by `jvm` and `jni_env` to instantiate a Java Virtual Machine.
57 # Used mostly for the FFI with Java.
58 protected fun create_default_jvm
60 var builder
= new JavaVMBuilder
62 # By default, look for Java classes in a jar file the same directory as the executable
63 builder
.options
.add
"-Djava.class.path={sys.program_name}.jar"
65 var jvm
= builder
.create_jvm
66 assert jvm
!= null else print
"JVM creation failed"
69 self.jni_env
= builder
.jni_env
.as(not null)
72 # Get a Java class by its name from the current `jni_env`
73 fun load_jclass
(name
: NativeString): JClass import jni_env
`{
74 JNIEnv *nit_ffi_jni_env = Sys_jni_env(self);
76 // retrieve the implementation Java class
77 jclass java_class = (*nit_ffi_jni_env)->FindClass(nit_ffi_jni_env, name);
78 if (java_class == NULL) {
79 fprintf(stderr, "Nit FFI with Java error: failed to load class.\\n");
80 (*nit_ffi_jni_env)->ExceptionDescribe(nit_ffi_jni_env);
88 # A standard Java string `java.lang.String`
90 # Converted to a Nit string using `to_s`, or to a C string with `to_cstring`.
91 # Created using `String::to_java_string` or `NativeString::to_java_string`.
92 extern class JavaString in "Java" `{ java.lang.String `}
95 # Get the string from Java and copy it to Nit memory
96 fun to_cstring: NativeString import sys, Sys.jni_env `{
97 Sys sys
= JavaString_sys(self);
98 JNIEnv *env
= Sys_jni_env(sys
);
100 // Get the data from
Java
101 const char
*java_cstr
= (*env
)->GetStringUTFChars(env
, self, NULL);
102 jsize len
= (*env
)->GetStringUTFLength(env
, self);
104 // Copy it
in control of
Nit
105 char
*nit_cstr
= (char
*)malloc
(len
+1);
106 memcpy
(nit_cstr
, java_cstr
, len
);
107 nit_cstr
[len
] = '\0';
109 // Free JNI ref
and return
110 (*env
)->ReleaseStringUTFChars(env
, self, java_cstr
);
114 redef fun to_s do return to_cstring.to_s
117 redef class NativeString
118 # Get a Java string from this C string
120 # This instance is only valid until the next execution of Java code.
121 # You can use `new_local_ref
` to keep it longer.
122 fun to_java_string: JavaString import sys, Sys.jni_env `{
123 Sys sys
= JavaString_sys(self);
124 JNIEnv *env
= Sys_jni_env(sys
);
125 return (*env
)->NewStringUTF(env
, self);
130 # Get `self` as a `JavaString`
131 fun to_java_string: JavaString do return to_cstring.to_java_string
134 redef extern class JavaObject
136 # Returns a global reference to the Java object behind this reference
138 # You must use a global reference when keeping a Java object
139 # across execution of Java code, per JNI specification.
140 fun new_global_ref: SELF import sys, Sys.jni_env `{
141 Sys sys
= JavaObject_sys(self);
142 JNIEnv *env
= Sys_jni_env(sys
);
143 return (*env
)->NewGlobalRef(env
, self);
146 # Delete this global reference
147 fun delete_global_ref import sys, Sys.jni_env `{
148 Sys sys
= JavaObject_sys(self);
149 JNIEnv *env
= Sys_jni_env(sys
);
150 (*env
)->DeleteGlobalRef(env
, self);
153 # Delete this local reference
154 fun delete_local_ref import sys, Sys.jni_env `{
155 Sys sys
= JavaObject_sys(self);
156 JNIEnv *env
= Sys_jni_env(sys
);
157 (*env
)->DeleteLocalRef(env
, self);
160 # Pops the current local reference frame and return a valid reference to self
162 # Similar to `JavaVM::pop_local_frame
` but returns a value.
163 fun pop_from_local_frame: SELF
165 var jni_env = sys.jni_env
166 return pop_from_local_frame_with_env(jni_env)
169 # Java implementation of `pop_from_local_frame
`
170 protected fun pop_from_local_frame_with_env(jni_env: JniEnv): SELF `{
171 return (*jni_env
)->PopLocalFrame(jni_env
, self);
174 # Is `self` null in Java?
176 # Since Java type system doesn't have the same `nullable` concept as Nit's,
177 # the two systems are not directly compatible. Any Nit instances of
178 # `JavaObject` may hold a Java null.
180 # To benefit from the safer type system of Nit, it is recommended to check
181 # the return of all extern methods implemented in Java to ensure the value
182 # is not a Java null. In case it is, you should replace it by a normal Nit
184 fun is_java_null: Bool in "Java" `{ return self == null; `}
186 # `JavaString` representation of `self` using Java's `toString`
187 fun to_java_string
: JavaString in "Java" `{ return self.toString(); `}
189 # Use Java's `toString
` for any `JavaObject`
192 if is_java_null then return super
193 return to_java_string.to_s