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[Hello-Core] Add "low level" sample. (#1047)
Rename `samples/Hello` to `samples/Hello-Java.Base`, as that sample exercises the `src/Java.Base` binding.
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| <Project Sdk="Microsoft.NET.Sdk"> | ||
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| <PropertyGroup> | ||
| <TargetFramework>$(DotNetTargetFramework)</TargetFramework> | ||
| <OutputType>Exe</OutputType> | ||
| <RootNamespace>Hello</RootNamespace> | ||
| <ImplicitUsings>enable</ImplicitUsings> | ||
| <Nullable>enable</Nullable> | ||
| <AllowUnsafeBlocks>true</AllowUnsafeBlocks> | ||
| </PropertyGroup> | ||
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| <ItemGroup> | ||
| <PackageReference Include="Mono.Options" /> | ||
| </ItemGroup> | ||
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| <ItemGroup> | ||
| <ProjectReference Include="..\..\src\Java.Interop\Java.Interop.csproj" /> | ||
| <ProjectReference Include="..\..\src\Java.Runtime.Environment\Java.Runtime.Environment.csproj" /> | ||
| </ItemGroup> | ||
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| </Project> |
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| using Java.Interop; | ||
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| using Mono.Options; | ||
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| bool showHelp = false; | ||
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| var jreOptions = new JreRuntimeOptions { | ||
| }; | ||
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| var options = new OptionSet { | ||
| "Using the JVM from C#!", | ||
| "", | ||
| "Options:", | ||
| { "jvm=", | ||
| $"{{PATH}} to JVM to use.", | ||
| v => jreOptions.JvmLibraryPath = v }, | ||
| { "cp=|classpath", | ||
| $"Add {{JAR-OR-DIRECTORY}} to JVM classpath.", | ||
| v => jreOptions.ClassPath.Add (v)}, | ||
| { "J=", | ||
| $"Pass the specified option to the JVM.", | ||
| v => jreOptions.AddOption (v) }, | ||
| { "h|help", | ||
| "Show this message and exit.", | ||
| v => showHelp = v != null }, | ||
| }; | ||
| options.Parse (args); | ||
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| if (showHelp) { | ||
| options.WriteOptionDescriptions (Console.Out); | ||
| return; | ||
| } | ||
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| if (string.IsNullOrEmpty (jreOptions.JvmLibraryPath) || !File.Exists (jreOptions.JvmLibraryPath)) { | ||
| Error ("Option -jvm=PATH is required. PATH is a full path to the JVM native library to use, e.g. `libjli.dylib`."); | ||
| return; | ||
| } | ||
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| var jre = jreOptions.CreateJreVM (); | ||
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| // We now have a JVM! | ||
| // The current thread is implicitly attached to the JVM. | ||
| // Access of `JniEnvironment` members on other threads will implicitly attach those threads to the JVM. | ||
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| // | ||
| // Useful background info: the JNI documentation! https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/functions.html | ||
| // | ||
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| var Object_class = JniEnvironment.Types.FindClass ("java/lang/Object"); | ||
| Console.WriteLine ($"Object_class={Object_class}"); | ||
| var Object_ctor = JniEnvironment.InstanceMethods.GetMethodID (Object_class, "<init>", "()V"); | ||
| var Object_val = JniEnvironment.Object.NewObject (Object_class, Object_ctor); | ||
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| Console.WriteLine ($"Object_val={Object_val}"); | ||
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| // Invoke `Object.toString()` | ||
| var Object_toString = JniEnvironment.InstanceMethods.GetMethodID (Object_class, "toString", "()Ljava/lang/String;"); | ||
| unsafe { | ||
| var Object_desc = JniEnvironment.InstanceMethods.CallObjectMethod (Object_val, Object_toString, null); | ||
| Console.WriteLine ($"Object_val.toString()={JniEnvironment.Strings.ToString (Object_desc)}"); | ||
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| // When JNI returns a `jobject` or `jclass` value, JNI returns a *JNI Object Reference*. | ||
| // The `JniObjectReference` struct is used to store JNI Local, Global, and Weak Global references. | ||
| // | ||
| // When an object reference is no longer required, it should be explicitly deleted. | ||
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| JniObjectReference.Dispose (ref Object_desc); | ||
| } | ||
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| JniObjectReference.Dispose (ref Object_class); | ||
| JniObjectReference.Dispose (ref Object_val); | ||
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| // There are some OO wrappers over the core `JniEnvironment` members. `JniType` is useful. | ||
| var Object_type = new JniType ("java/lang/Object"); | ||
| var Object_ctor2 = Object_type.GetConstructor ("()V"); | ||
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| unsafe { | ||
| var Object_val2 = Object_type.NewObject (Object_ctor2, null); | ||
| var Object_desc = JniEnvironment.InstanceMethods.CallObjectMethod (Object_val2, Object_toString, null); | ||
| Console.WriteLine ($"Object_val.toString()={JniEnvironment.Strings.ToString (Object_desc)}"); | ||
| } | ||
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| void Error (string message) | ||
| { | ||
| var app = Path.GetFileNameWithoutExtension (Environment.GetCommandLineArgs ()[0]); | ||
| Console.Error.WriteLine ($"{app}: {message}"); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
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| # Hello-Core | ||
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| Use as little of `Java.Interop.dll` as possible. No object mapping. | ||
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| Usage: | ||
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| ``` | ||
| Options: | ||
| --jvm=PATH PATH to JVM to use. | ||
| --cp, --classpath=JAR-OR-DIRECTORY | ||
| Add JAR-OR-DIRECTORY to JVM classpath. | ||
| -J=VALUE Pass the specified option to the JVM. | ||
| -h, --help Show this message and exit. | ||
| ``` | ||
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| `-J` can be used to add runtime options to the JVM instance, e.g. | ||
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| ```shell | ||
| # Enable verbose JNI logging from the JVM | ||
| % dotnet run -- --jvm /Library/Java/JavaVirtualMachines/microsoft-11.jdk/Contents/Home/lib/jli/libjli.dylib -J-verbose:jni | ||
| [Dynamic-linking native method java.lang.Object.registerNatives ... JNI] | ||
| [Registering JNI native method java.lang.Object.hashCode] | ||
| [Registering JNI native method java.lang.Object.wait] | ||
| … | ||
| ``` | ||
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| The sample will create a `java.lang.Object` instance and invoke `Object.toString()` on it. | ||
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| ``` | ||
| % dotnet run -- --jvm /Library/Java/JavaVirtualMachines/microsoft-11.jdk/Contents/Home/lib/jli/libjli.dylib | ||
| Object_class=0x7ff04f105b98/L | ||
| Object_val=0x7ff04f105ba8/L | ||
| Object_val.toString()=java.lang.Object@5cbc508c | ||
| Object_val.toString()=java.lang.Object@3419866c | ||
| ``` |
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