使用Java Native Access (JNA)呼叫MacOS API

介紹

這是一個關於如何將 JNA 與 MacOS API 結合使用的簡單範例。我不打算解釋這一點，因為我仍在學習，但我將程式碼保持在最低限度，以便更容易理解並了解如何將其用於其他目的的基本概念。

大部分程式碼來自 Intellij-Community（Apache 授權）。

依賴性

我們需要的只是 jna-platform。

<dependency>
  <groupId>net.java.dev.jna</groupId>
  <artifactId>jna-platform</artifactId>
  <version>5.13.0</version>
</dependency>

程式碼

總共有4個原始碼檔案。 ID 是從 IntelliJ 複製而來，未經修改。 MyFoundation 和 MyFoundationLibrary 分別是從 Foundation 和 FoundationLibrary 修剪出來的。

應用程式.java

package org.example;

import com.sun.jna.Pointer;

import static org.example.MyFoundation.*;

public class Application {

    public static void main(String[] args) throws Exception {
        ID processInfoCls = getObjcClass("NSProcessInfo");
        Pointer processInfoSel = createSelector("processInfo");
        Pointer processNameSel = createSelector("processName");

        ID processInfo = invoke(processInfoCls, processInfoSel);
        ID processNameNSString = invoke(processInfo, processNameSel);
        String processName = toStringViaUTF8(processNameNSString);
        System.out.println(processName);
    }

}

ID.java

package org.example;

import com.sun.jna.NativeLong;

public final class ID extends NativeLong {

    public ID() {
    }

    public ID(long peer) {
        super(peer);
    }

    public static final ID NIL = new ID(0L);

    public boolean booleanValue() {
        return intValue() != 0;
    }
}

MyFoundationLibrary.java

public interface MyFoundationLibrary extends Library {

    int kCFStringEncodingUTF8 = 0x08000100;

    ID objc_getClass(String className);

    Pointer sel_registerName(String selectorName);

    int CFStringGetLength(ID theString);

    byte CFStringGetCString(ID theString, byte[] buffer, int bufferSize, int encoding);

}

MyFoundation.java

package org.example;

import com.sun.jna.*;

import java.lang.reflect.Proxy;
import java.util.Collections;

public class MyFoundation {
    private static final MyFoundationLibrary myFoundationLibrary;
    private static final Function myObjcMsgSend;

    static {
        myFoundationLibrary = Native.load("Foundation", MyFoundationLibrary.class, Collections.singletonMap("jna.encoding", "UTF8"));
        NativeLibrary nativeLibrary = ((Library.Handler) Proxy.getInvocationHandler(myFoundationLibrary)).getNativeLibrary();
        myObjcMsgSend = nativeLibrary.getFunction("objc_msgSend");
    }

    public static ID getObjcClass(String className) {
        return myFoundationLibrary.objc_getClass(className);
    }

    public static Pointer createSelector(String s) {
        return myFoundationLibrary.sel_registerName(s);
    }

    private static Object [] prepInvoke(ID id, Pointer selector, Object[] args) {
        Object[] invokArgs = new Object[args.length + 2];
        invokArgs[0] = id;
        invokArgs[1] = selector;
        System.arraycopy(args, 0, invokArgs, 2, args.length);
        return invokArgs;
    }

    public static ID invoke(final ID id, final Pointer selector, Object... args) {
        // objc_msgSend is called with the calling convention of the target method
        // on x86_64 this does not make a difference, but arm64 uses a different calling convention for varargs
        // it is therefore important to not call objc_msgSend as a vararg function
        return new ID(myObjcMsgSend.invokeLong(prepInvoke(id, selector, args)));
    }

    public static String toStringViaUTF8(ID cfString) {
        if (ID.NIL.equals(cfString)) return null;

        int lengthInChars = myFoundationLibrary.CFStringGetLength(cfString);
        int potentialLengthInBytes = 3 * lengthInChars + 1; // UTF8 fully escaped 16 bit chars, plus nul

        byte[] buffer = new byte[potentialLengthInBytes];
        byte ok = myFoundationLibrary.CFStringGetCString(cfString, buffer, buffer.length, MyFoundationLibrary.kCFStringEncodingUTF8);
        if (ok == 0) throw new RuntimeException("Could not convert string");
        return Native.toString(buffer);
    }

}

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