最近專案收到個需求，需要呼叫c寫的函式，給的是so檔案，查閱了資料，so檔案為linux下的動態庫函式檔案，windos下為dll檔案。傳統方案用JNI方式進行連線，大致看了下JNI方式實在麻煩，崩潰中找到JNA，併成功實現了呼叫，特此記錄使用過程。

一、將so檔案放在linux伺服器下，並且指定export LD_LIBRARY_PATH路徑為你的so檔案放置路徑（so檔案需要字首lib，因為jna為去動態庫中匹配lib字首的so檔案，如libcompress.so）

我這邊放置在/etc/profile

vim /etc/profile然後設定

export LD_LIBRARY_PATH=你的so檔案放置路徑
 

編寫好後執行：source /etc/profile使之生效 

二、maven匯入jna包

<!-- https://mvnrepository.com/artifact/com.sun.jna/jna -->
    <dependency>
      <groupId>com.sun.jna</groupId>
      <artifactId>jna</artifactId>
      <version>3.0.9</version>
    </dependency>

三、根據c提供的標頭檔案看需要呼叫的方法和其引數，在java下建立

c中格式如下：

#define uint8_t     unsigned char
#define uint16_t    unsigned short



#define COMPRESS_IR_MAX_DIF_VAL     (255) //the max different value of the ir data
#define COMPRESS_INDEX_LEN_3        (3)
#define COMPRESS_INDEX_LEN_4        (4)
#define COMPRESS_INDEX_LEN_5        (5)
#define COMPRESS_INDEX_LEN_6        (6)
#define COMPRESS_INDEX_LEN_7        (7)
#define COMPRESS_INDEX_LEN_8        (8)

#define COMPRESS_VAGUE_MAX_VALUE    	(20)//樣品資料最大模糊值
#define COMPRESS_SRC_DATA_DIVIDE_VAL	(5)//原資料整除值


typedef struct
{
    uint16_t    freq;            //frequency
    int     *srcData;       //sourdata pointer
    uint16_t    srcSize;        //source data size
    uint16_t     *diffData;      //different value buffer pointer
    uint8_t     diffSize;      //different value count
    uint8_t     *indexBuf;      //index buffer pointer
    uint16_t    indexBufSize;   //index buffer Size
    uint16_t    indexSize;     //size of the index list
    uint8_t     indexLen;       //the length of the single index value
}COMPRESS_INFO;


typedef struct
{
    int     freq;           //frequency
    int     srcData[2000];      //source data
    uint16_t srcSize;       //source data Size
}COMPRESS_INPUT;

typedef struct
{
    int			compressDataSize;
    uint8_t     compressData[2000]; //compress data pointer
}COMPRESS_OUTPUT;
typedef struct
{
    uint8_t data2:2;
    uint8_t data1:3;
    uint8_t data0:3;

    uint8_t data6:1;
    uint8_t data5:3;
    uint8_t data4:3;
    uint8_t data3:1;

    uint8_t data9:3;
    uint8_t data8:3;
    uint8_t data7:2;
}UNIT_3;
typedef struct
{
    uint8_t data0:4;
    uint8_t data1:4;
}UNIT_4;

typedef struct
{
    uint8_t data1:3;
    uint8_t data0:5;

    uint8_t data4:1;
    uint8_t data3:5;
    uint8_t data2:2;

    uint8_t data6:4;
    uint8_t data5:4;

    uint8_t data9:2;
    uint8_t data8:5;
    uint8_t data7:1;

    uint8_t data11:5;
    uint8_t data10:3;
}UNIT_5;
typedef struct
{
    uint8_t data1:2;
    uint8_t data0:6;

    uint8_t data3:4;
    uint8_t data2:4;

    uint8_t data5:6;
    uint8_t data4:2;
}UNIT_6;
typedef struct
{
    uint8_t data1:1;
    uint8_t data0:7;

    uint8_t data3:2;
    uint8_t data2:6;

    uint8_t data5:3;
    uint8_t data4:5;

    uint8_t data7:4;
    uint8_t data6:4;

    uint8_t data9:5;
    uint8_t data8:3;

    uint8_t data11:6;
    uint8_t data10:2;

    uint8_t data13:7;
    uint8_t data12:1;
}UNIT_7;
COMPRESS_OUTPUT * compress_handle(COMPRESS_INPUT *inputData);
 

由上可知，c中提供的為一個簡單壓縮方法，引數為COMPRESS_INPUT，返回值為COMPRESS_OUT兩個物件除了有基本資料型別，還有byte型別和int型別指標。如果引數或者返回值都只是基本型別，很簡單，這邊不講，這種引數返回值都為物件，並且屬性涉及指標（java沒有指標的概念），稍微複雜一些，廢話不多說，直接上程式碼，首先建立入參物件：

package com.intre.kksdk.bean;

import com.sun.jna.Structure;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

/**
 * Created by YQ11053 on 2018/8/28 0028.
 */
public class COMPRESS_INPUT extends Structure implements Serializable {

    public int freq;
    public int[] srcData = new int[2000];
    public int srcSize;

    public COMPRESS_INPUT() {
        allocateMemory();
    }

    public static class ByReference extends COMPRESS_INPUT implements Structure.ByReference {}
    public static class ByValue extends COMPRESS_INPUT implements Structure.ByValue {}

    @Override
    protected List<String> getFieldOrder() {
        List<String> Field = new ArrayList<String>();
        Field.add("freq");
        Field.add("srcData");
        Field.add("srcSize");
        return Field;
    }

    public int getFreq() {
        return freq;
    }

    public void setFreq(int freq) {
        this.freq = freq;
    }

    public int[] getSrcData() {
        return srcData;
    }

    public void setSrcData(int[] srcData) {
        this.srcData = srcData;
    }

    public int getSrcSize() {
        return srcSize;
    }

    public void setSrcSize(int srcSize) {
        this.srcSize = srcSize;
    }


}

上面需要注意點如下：

1、類需要繼承Structure    //這樣才能接受c中的結構體

2、用int型別的陣列去對應c中int型別的指標，並且直接初始化並設定大小

3、建構函式中執行allocateMemory();，允許計算大小

4、建立（一般都寫上）

public static class ByReference extends COMPRESS_INPUT implements Structure.ByReference {}  //引數為物件需要這麼寫
public static class ByValue extends COMPRESS_INPUT implements Structure.ByValue {}  //為基本型別這麼寫

5、重寫方法getFieldOrder,實現c的結構體和java的物件屬性值的傳遞

@Override
protected List<String> getFieldOrder() {
    List<String> Field = new ArrayList<String>();
    Field.add("freq");
    Field.add("srcData");
    Field.add("srcSize");
    return Field;
}

返回值物件同上：

package com.intre.kksdk.bean;

import com.sun.jna.Structure;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Created by YQ11053 on 2018/8/28 0028.
 */
public class COMPRESS_OUTPUT extends Structure implements Serializable {

    public int compressDataSize;
    public byte[] compressData = new byte[2000];

    public COMPRESS_OUTPUT(){
        allocateMemory();
    }

    public static class ByReference extends COMPRESS_OUTPUT implements Structure.ByReference {}
    public static class ByValue extends COMPRESS_OUTPUT implements Structure.ByValue {}

    @Override
    protected List<String> getFieldOrder() {
        List<String> Field = new ArrayList<String>();
        Field.add("compressDataSize");
        Field.add("compressData");

        return Field;
    }

    @Override
    public String toString() {
        return "CompressOutput{" +
                "compressData=" + Arrays.toString(compressData) +
                ", compressDataSize=" + compressDataSize +
                '}';
    }
}

實現類：

package com.intre.kksdk.utils;

import com.intre.kksdk.bean.COMPRESS_INPUT;
import com.intre.kksdk.bean.COMPRESS_OUTPUT;
import com.intre.kksdk.bean.DECOMPRESS_INPUT;
import com.intre.kksdk.bean.DECOMPRESS_OUTPUT;
import com.sun.jna.Library;
import com.sun.jna.Native;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Created by YQ11053 on 2018/8/28 0028.
 */
public class CompressJNA {

    private  Logger logger = LoggerFactory.getLogger(CompressJNA.class);


    public interface CompressLib extends Library {
        CompressLib INSTANCE = (CompressLib) Native.loadLibrary("compress",CompressLib.class);
        COMPRESS_OUTPUT.ByReference compress_handle(COMPRESS_INPUT compress_input); //壓縮方法
        
    }

    public  COMPRESS_OUTPUT.ByReference compress_handle(COMPRESS_INPUT compress_input){
        return CompressLib.INSTANCE.compress_handle(compress_input);
    }

    public COMPRESS_OUTPUT.ByReference compress(COMPRESS_INPUT compress_input){
        COMPRESS_OUTPUT.ByReference compressOutput = new CompressJNA().compress_handle(compress_input);
        return compressOutput;
    }

   

}

需要注意的是載入so檔案方法中,CompressLib INSTANCE = (CompressLib) Native.loadLibrary("compress",CompressLib.class);

第一個引數為so檔案出去lib字首後的名稱.

四、呼叫（windos下無法測試，需要在linux下才能執行成功，windos下可用dll檔案）

 public static void main(String[]args){
        int frec = 3600;
        COMPRESS_INPUT inputData = new COMPRESS_INPUT();
        inputData.setFreq(frec);
        int[] srcData= {2,1,4,5,6,7,8,9};
        int srcDataSize = 8;
        inputData.setSrcData(srcData);
        inputData.setSrcSize(srcDataSize);
        COMPRESS_OUTPUT compressOutput = new CompressJNA().compress(inputData); //呼叫so函式獲取壓縮物件
    }

ps：伺服器由於某些原因關閉重啟後需要重新執行source /etc/profile  然後再啟動tomcat使之生效。