ubuntu中java开发环境搭建

2023-01-18 1815 words 4 minutes

Contents

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1. VSCODE 插件
2. ubuntu20.04安装Java
3. java 编译
4. JNI

1. VSCODE 插件

Code Runner
Extension Pack for Java
Maven for Java
Debugger for Java
Test Runner for Java
Project Manager for Java
Language Support for Java(TM) by Red Hat
Java Debugger

2. ubuntu20.04安装Java

默认的ubuntu20.04源仓库包含了两个openJDK软件包，Java Runtime Environment(JRE)和Java Development Kit(JDK)。JRE主要包含了Java虚拟机(JVM),类和允许你允许Java程序的二进制包。JDK包含JRE和用于构建Java应用的开发/调试工具和库文件. Java11s java的一个长期支持版本，同时也是Ubuntu20.04的默认Java开发和运行环境。

安装

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2
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sudo apt-get update
sudo apt-get -y install openjdk-11-jdk
java --version

设置Java默认版本
1 2

java --version sudo update-alternatives --config java
已经安装的Java版本都会输出，输入想要设置为默认的序列化，按enter即可

Java_HOME环境变量

# 首先查看Java的安装位置
update-alternatives --config java

# 打开/etc/environment文件
sudo vim /etc/environment
# 将JAVA_HOME指定到OpenJDK11，在文件末尾添加
JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64"

# 运行下述命令让shell生效
source /etc/environment

# 验证JAVA_HOME环境变量
echo $JAVA_HOME

vscode Java_HOME环境变量配置

settings.json

`1`	`"java.jdt.ls.java.home": "/usr/lib/jvm/java-11-openjdk-amd64",`

3. java 编译

# 编译单个文件
javac test.java
javac test

# package
javac -d . *.java
java animals/MammalInt

javac -d ../ JNIDemo.java Java2Cplusplus.java BaseClass.java
javac test.java
java -Djava.library.path=./JNIDemo  test

# JNI
javac -h . JNIDemo.java
javap -s -p  Java2Cplusplus.class

# cpp
g++ -fPIC -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/ -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/linux/ -shared -o libcom_huhu_test_JNIDemo.so com_huhu_test_JNIDemo.cpp

4. JNI

4.1. JAVA调用C++

import com.huhu.test.*;
/* 文件名 : MammalInt.java */
public class test
{
    public static void main(String[] args)
    {
        //加载C文件
        System.loadLibrary("com_huhu_test_JNIDemo");
        JNIDemo jniDemo = new JNIDemo();
        jniDemo.testHello();
        int[] data = {1, 2, 3};
        float[] f = jniDemo.execute(data, 1, 2, 3);

        System.out.println(f[0]);
        System.out.println(f[1]);
        System.out.println(f[2]);
    }
}

4.2. 生成头文件 com_huhu_test_JNIDemo

`1`	`javac -h . JNIDemo.java`

JNIDemo.java ：

package com.huhu.test;

public class JNIDemo
{
    //定义一个方法，该方法在C中实现
    public native void testHello();
    public native float[] execute(int[] data, int width, int height, float ep);
}

com_huhu_test_JNIDemo.h :

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_huhu_test_JNIDemo */

#ifndef _Included_com_huhu_test_JNIDemo
#define _Included_com_huhu_test_JNIDemo
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_huhu_test_JNIDemo
 * Method:    testHello
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_huhu_test_JNIDemo_testHello
  (JNIEnv *, jobject);

/*
 * Class:     com_huhu_test_JNIDemo
 * Method:    execute
 * Signature: ([IIIF)[F
 */
JNIEXPORT jfloatArray JNICALL Java_com_huhu_test_JNIDemo_execute
  (JNIEnv *, jobject, jintArray, jint, jint, jfloat);

#ifdef __cplusplus
}
#endif
#endif

4.3. 实现 com_huhu_test_JNIDemo

com_huhu_test_JNIDemo.cpp:

// g++ -fPIC -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/ -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/linux/ -shared -o libTestJni.so
// TestJni.cpp
#include "com_huhu_test_JNIDemo.h"

#include <jni.h>

#include <cstdio>
#include <iostream>
#include <vector>

#define JNI_JAVA2C_PATH "com/huhu/test/Java2Cplusplus"
#define JNI_BASE_CLASS_PATH "com/huhu/test/BaseClass"

JNIEXPORT void JNICALL Java_com_huhu_test_JNIDemo_testHello(JNIEnv *env, jobject thiz)
{
    std::cout << "this is Java_com_huhu_test_JNIDemo_testHello C++ print" << std::endl;
}

JNIEXPORT jfloatArray JNICALL Java_com_huhu_test_JNIDemo_execute(JNIEnv *env, jobject thiz, jintArray data, jint width, jint height, jfloat ep)
{
    std::cout << "this is Java_com_huhu_test_JNIDemo_execute C++ print" << std::endl;
    unsigned char *data_src = (unsigned char *)env->GetIntArrayElements(data, NULL);
    std::cout << "data_src " << data_src[0] << " " << data_src[1] << " " << data_src[2] << " " << std::endl;

    std::cout << "width height ep " << width << " " << height << " " << ep << " " << std::endl;

    std::vector<float> result{0.1, 0.2, 0.3};

    jfloatArray resultArray = env->NewFloatArray(result.size());
    env->SetFloatArrayRegion(resultArray, 0, result.size(), &result[0]);

    /* ------------------ */
    //步骤1：
    jclass clazz = env->FindClass(JNI_JAVA2C_PATH);

    //步骤2：<init>是java的构造函数名，这个有点特殊。在我的一篇文章jetpack中的问题中碰见过它。
    //构造函数没输入输出参数，所以这里的signature填写为()V
    jmethodID method_init_id = env->GetMethodID(clazz, "<init>", "()V");
    jmethodID method_set_id = env->GetMethodID(clazz, "setNum", "(I)V");
    jmethodID method_get_id = env->GetMethodID(clazz, "getNum", "()I");

    jclass base = env->FindClass(JNI_BASE_CLASS_PATH);
    jmethodID method_base_init_id = env->GetMethodID(base, "<init>", "()V");
    jobject objbase = env->NewObject(base, method_base_init_id);

    jmethodID method_get_jobject_id = env->GetMethodID(clazz, "getNum", "(Lcom/huhu/test/BaseClass;)I");

    //步骤3：
    //创建了 Java2Cplusplus 对象
    jobject obj = env->NewObject(clazz, method_init_id);

    //步骤4:调用相应的方法
    env->CallVoidMethod(obj, method_set_id, 21);        // set函数没返回值
    int year = env->CallIntMethod(obj, method_get_id);  // getYear有返回值

    int year2 = env->CallIntMethod(obj, method_get_jobject_id,objbase);  // getYear有返回值

    std::cout << "year " << year << std::endl;
    std::cout << "year2 " << year2 << std::endl;

    /* ------------------ */

    return resultArray;
}

4.4. 编译 com_huhu_test_JNIDemo.cpp

g++ -fPIC -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/ -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/linux/ -shared -o libcom_huhu_test_JNIDemo.so com_huhu_test_JNIDemo.cpp


g++ -fPIC -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/ -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/linux/ -shared -o libcom_huhu_test_UfcwStrategy.so com_huhu_test_UfcwStrategy.cpp

g++ -fPIC -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/ -I /usr/lib/jvm/java-1.11.0-openjdk-amd64/include/linux/ -shared -o libcom_ufcw_strategy_UfcwStrategy.so com_ufcw_strategy_UfcwStrategy.cpp

4.5. 编译运行 java


javac -d ../ JNIDemo.java Java2Cplusplus.java BaseClass.java


cd ../

javac test.java

java -Djava.library.path=./JNIDemo  test

4.6. JNI GetFieldID和GetMethodID 所需签名参数

调用JNI的GetMethodID函数获取一个jmethodID时，需要传入一个方法名称和方法签名，方法名称就是在Java中定义的方法名，方法签名的格式为：(形参参数类型列表)返回值。

1.基本类型签名

Java	Native	Signature
byte	jbyte	B
char	jchar	C
double	jdouble	D
float	jfloat	F
int	jint	I
short	jshort	S
long	jlong	J
boolean	jboolean	Z
void	void	V

2.引用数据类型的转换.

Java	Native	Signature
所有对象	jobject	L+classname +;
Class	jclass	Ljava/lang/Class;
String	jstring	Ljava/lang/String;
Throwable	jthrowable	Ljava/lang/Throwable;
Object[]	jobjectArray	[L+classname +;
byte[]	jbyteArray	[B
char[]	jcharArray	[C
double[]	jdoubleArray	[D
float[]	jfloatArray	[F
int[]	jintArray	[I
short[]	jshortArrsy	[S
long[]	jlongArray	[J
boolean[]	jbooleanArray	[Z

获取签名方式：

自己拼写

方法：int (int param);

签名：(I)I

命令行生成

1、使用javac，生成对应java文件的class文件；

2、使用 javap -s -p 命令获取对应签名信息，如图：

Compiled from "Java2Cplusplus.java"
public class com.huhu.test.Java2Cplusplus {
  private int num;
    descriptor: I
  public com.huhu.test.Java2Cplusplus();
    descriptor: ()V

  public void setNum(int);
    descriptor: (I)V

  public int getNum();
    descriptor: ()I

  public int getBaseClassNum(com.huhu.test.BaseClass);
    descriptor: (Lcom/huhu/test/BaseClass;)I
}