Introduction
Here is a simple example about how to use JNA with MacOS API. I am not going to explain this, because I am still learning, but I keep code minimal to make it easier to understand and get the basic idea about how to do it for other purposes.
Most of the code is fromIntellij-Community (Apache License).
Dependency
All we need isjna-platform.
<dependency> <groupId>net.java.dev.jna</groupId> <artifactId>jna-platform</artifactId> <version>5.13.0</version></dependency>Code
There are totally 4 source code files.ID is copied from IntelliJ without modification.MyFoundation andMyFoundationLibrary are trimmed fromFoundation andFoundationLibrary respectively.
Application.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); }}Top comments(0)
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