jdk怎么编写java程序,java中的nio架构

接着上一篇文章继续来说：
地址
https://mp.csdn.net/mdeditor/85546883#

交互之前，说几个概念性的东西：
jni调用思想：

找到对应的类 -jclass 找到对应的方法 -jmethonID调用相关方法 CallVoidMethid释放相关资源就行了

以及生成方法的签名，native方法，在生成头文件时 会自动带有注释，需要手动生成java文件的方法签名，方法如下：
在appbuildintermediatesclasses目录下输入如下命令：
javap -s 包名+类名 生成方法的签名

以及c调用java实例方法步骤：

1，找到对应的class --findClass 2, 然后调用其构造方法 GetMethodID 3, 创建其对象 NewObject 4,调用其方法

同样，第一步，编写java层代码的静态方法，实例方法，和字段

public class MyFirstJni { private String addRess = "beijing"; private static String name = "nata"; static { System.loadLibrary("firstC"); } public static void loadMessage(String data){ Log.d("data", data); } public void method(String data){ loadMessage(data); loadMessage(addRess); } public static void staticMethod(String data){ loadMessage(data); loadMessage(name); }//java调用jni public static native String getJniData(); public static native void callStaticMethod(int c); public static native void callStaticMethod(long i,String str); public native void callInstanceMethod(int i); public native void callInstanceMethod(String str,long i);}

第二步：生成头文件

/* DO NOT EDIT THIS FILE - it is machine generated */#include <jni.h>/* Header for class com_example_a13940_myapplication_MyFirstJni */#ifndef _Included_com_example_a13940_myapplication_MyFirstJni#define _Included_com_example_a13940_myapplication_MyFirstJni#ifdef __cplusplusextern "C" {#endif/* * Class: com_example_a13940_myapplication_MyFirstJni * Method: getJniData * Signature: ()Ljava/lang/String; */JNIEXPORT jstring JNICALL Java_com_example_a13940_myapplication_MyFirstJni_getJniData (JNIEnv *, jclass);/* * Class: com_example_a13940_myapplication_MyFirstJni * Method: callStaticMethod * Signature: (I)V */JNIEXPORT void JNICALL Java_com_example_a13940_myapplication_MyFirstJni_callStaticMethod__I (JNIEnv *, jclass, jint);/* * Class: com_example_a13940_myapplication_MyFirstJni * Method: callStaticMethod * Signature: (JLjava/lang/String;)V */JNIEXPORT void JNICALL Java_com_example_a13940_myapplication_MyFirstJni_callStaticMethod__JLjava_lang_String_2 (JNIEnv *, jclass, jlong, jstring);/* * Class: com_example_a13940_myapplication_MyFirstJni * Method: callInstanceMethod * Signature: (I)V */JNIEXPORT void JNICALL Java_com_example_a13940_myapplication_MyFirstJni_callInstanceMethod__I (JNIEnv *, jobject, jint);/* * Class: com_example_a13940_myapplication_MyFirstJni * Method: callInstanceMethod * Signature: (Ljava/lang/String;J)V */JNIEXPORT void JNICALL Java_com_example_a13940_myapplication_MyFirstJni_callInstanceMethod__Ljava_lang_String_2J (JNIEnv *, jobject, jstring, jlong);#ifdef __cplusplus}#endif#endif

第三步：编写cpp文件中调用java方法 和jni方法的具体实现

//// Created by 13940 on 2019/1/1.//#include "com_example_a13940_myapplication_MyFirstJni.h"//java调用jni方法JNIEXPORT jstring JNICALL Java_com_example_a13940_myapplication_MyFirstJni_getJniData (JNIEnv * env, jclass jcls){ return env->NewStringUTF("FORM C DATA"); }/* * Class: com_example_a13940_myapplication_MyFirstJni * Method: callStaticMethod * Signature: (I)V */ //调用静态方法 和修改成员变量JNIEXPORT void JNICALL Java_com_example_a13940_myapplication_MyFirstJni_callStaticMethod__I (JNIEnv * env, jclass jclassess, jint i){ //找到相关的类 注意路径是带反斜杆 不是带. jclass cls_First = env->FindClass("com/example/a13940/myapplication/MyFirstJni"); if(cls_First == NULL){ return; } /** 方法参数：类名，方法名，方法签名 */ //找到对应的方法 注意签名后面有冒号 jmethodID mtd_static_method = env->GetStaticMethodID(cls_First,"staticMethod","(Ljava/lang/String;)V"); if(mtd_static_method == NULL){ return; } //修改java中静态字段的值 获取成员变量 注意签名后面有冒号 jfieldID file_name = env->GetStaticFieldID(cls_First,"name","Ljava/lang/String;"); if(file_name == NULL){ return; } //定义静态字段的值 jstring name = env->NewStringUTF("TOM"); //对成员变量设置值 env ->SetStaticObjectField(cls_First,file_name,name); jstring data = env->NewStringUTF("call static method"); if(data == NULL){ return; } //调用java层静态方法 env ->CallStaticVoidMethod(cls_First,mtd_static_method,data); //删除引用 env->DeleteLocalRef(cls_First); env->DeleteLocalRef(name); env->DeleteLocalRef(data); } /* * Class: com_example_a13940_myapplication_MyFirstJni * Method: callInstanceMethod * Signature: (I)V */ //调用java实例方法 和修改实例变量 JNIEXPORT void JNICALL Java_com_example_a13940_myapplication_MyFirstJni_callInstanceMethod__I (JNIEnv *env, jobject jobj, jint i){ //找到对应的方法 jclass cls_First = env->FindClass("com/example/a13940/myapplication/MyFirstJni"); if(cls_First == NULL){ return; } //找到对应的方法 jmethodID mtd_method = env->GetMethodID(cls_First,"method","(Ljava/lang/String;)V"); if(mtd_method == NULL){ return; } //找到对应的构造方法 jmethodID mtd_construct = env->GetMethodID(cls_First,"<init>","()V"); if(mtd_construct == NULL){ return; } jfieldID fld_address = env->GetFieldID(cls_First,"addRess","Ljava/lang/String;"); if(fld_address == NULL){ return; } jstring address = env->NewStringUTF("shanghai"); if(address == NULL){ return; } //创建相应的对象 jobject oFirst = env->NewObject(cls_First,mtd_construct,NULL); if(oFirst == NULL){ return; } //注意此时的对象 应该是jobject对象 非jclass对象 env->SetObjectField(oFirst,fld_address,address); jstring message = env->NewStringUTF("call instance method"); //调用java层实例方法 注意此时的对象 应该是jobject对象 非jclass对象 env->CallVoidMethod(oFirst,mtd_method,message); //清除对象的引用 env->DeleteLocalRef(message); env->DeleteLocalRef(cls_First); env->DeleteLocalRef(oFirst); env->DeleteLocalRef(address); }

第四步：调用jni方法
new MyFirstJni().callInstanceMethod(2);
MyFirstJni.callStaticMethod(21);
viewById.setText(MyFirstJni.getJniData());

以上：仅仅只是自己写的代码 注释很多，代码质量不高，望谅解