Java code calls C code JNI

1 The interface for defining a C method is equivalent to the implementation of an interface interface defined in Java code that is implemented by the C language

public native int login (String password);

2 Implementing C code

In the directory of the Android project under SRC, you can use the command: (javah-jni full-class name) to generate a corresponding C-language function header file

#include <stdio.h>
#include "Com_qushaohui_aliwangwang_mainactivity.h"

int login (char* psw) {

char* rightpwd = "123";
if (strcmp (psw,rightpwd)) {
return 302;
}else{
return 200;
}
}

char* Jstring2cstr (jnienv* env, jstring jstr)
{
char* RTN = NULL;
Jclass clsstring = (*env)->findclass (env, "java/lang/string");
Jstring Strencode = (*env)->newstringutf (env, "GB2312");
Jmethodid mid = (*env)->getmethodid (env,clsstring, "GetBytes", "(ljava/lang/string;) [B");
Jbytearray barr= (Jbytearray) (*env)->callobjectmethod (Env,jstr,mid,strencode); String. GetByte ("GB2312");
Jsize alen = (*env)->getarraylength (Env,barr);
jbyte* ba = (*env)->getbytearrayelements (Env,barr,jni_false);
if (Alen > 0)
{
RTN = (char*) malloc (alen+1); "The"
memcpy (Rtn,ba,alen);
rtn[alen]=0;
}
(*env)->releasebytearrayelements (env,barr,ba,0); //
return RTN;
}

Jniexport Jint Jnicall Java_com_qushaohui_aliwangwang_mainactivity_login
(JNIENV * env, jobject obj, jstring str)
{
char* C = jstring2cstr (ENV,STR);
return login (c);
}

3 tell the compiler how to package C code into a function library to generate a android.mk file

Local_path: = $ (call My-dir)

Include $ (clear_vars)
# corresponding to the name of the function library
Local_module: = Hello
# files corresponding to C code
Local_src_files: = hello.c

Include $ (build_shared_library)

4 Packaging C code into a function library used in the installation environment

Execute Command ndk-build

5-Step introduction of library functions in Java code

6 How to use

Java code calls C code JNI