Java example source code file (JNI.java)

This example Java source code file (JNI.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

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Java - Java tags/keywords

boolean, byte, char, declared, double, executableelement, jni, list, short, string, typeelement, typemirror, typesignature, util, variableelement

The JNI.java Java example source code

/*
 * Copyright (c) 2002, 2010, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.tools.javah;

import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.lang.model.element.Element;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.type.ArrayType;
import javax.lang.model.type.TypeMirror;
import javax.lang.model.util.ElementFilter;


/**
 * Header file generator for JNI.
 *
 * <p>This is NOT part of any supported API.
 * If you write code that depends on this, you do so at your own
 * risk.  This code and its internal interfaces are subject to change
 * or deletion without notice.</b>

 *
 * @author  Sucheta Dambalkar(Revised)
 */
public class JNI extends Gen {
    JNI(Util util) {
        super(util);
    }

    public String getIncludes() {
        return "#include <jni.h>";
    }

    public void write(OutputStream o, TypeElement clazz) throws Util.Exit {
        try {
            String cname = mangler.mangle(clazz.getQualifiedName(), Mangle.Type.CLASS);
            PrintWriter pw = wrapWriter(o);
            pw.println(guardBegin(cname));
            pw.println(cppGuardBegin());

            /* Write statics. */
            List<VariableElement> classfields = getAllFields(clazz);

            for (VariableElement v: classfields) {
                if (!v.getModifiers().contains(Modifier.STATIC))
                    continue;
                String s = null;
                s = defineForStatic(clazz, v);
                if (s != null) {
                    pw.println(s);
                }
            }

            /* Write methods. */
            List<ExecutableElement> classmethods = ElementFilter.methodsIn(clazz.getEnclosedElements());
            for (ExecutableElement md: classmethods) {
                if(md.getModifiers().contains(Modifier.NATIVE)){
                    TypeMirror mtr = types.erasure(md.getReturnType());
                    String sig = signature(md);
                    TypeSignature newtypesig = new TypeSignature(elems);
                    CharSequence methodName = md.getSimpleName();
                    boolean longName = false;
                    for (ExecutableElement md2: classmethods) {
                        if ((md2 != md)
                            && (methodName.equals(md2.getSimpleName()))
                            && (md2.getModifiers().contains(Modifier.NATIVE)))
                            longName = true;

                    }
                    pw.println("/*");
                    pw.println(" * Class:     " + cname);
                    pw.println(" * Method:    " +
                               mangler.mangle(methodName, Mangle.Type.FIELDSTUB));
                    pw.println(" * Signature: " + newtypesig.getTypeSignature(sig, mtr));
                    pw.println(" */");
                    pw.println("JNIEXPORT " + jniType(mtr) +
                               " JNICALL " +
                               mangler.mangleMethod(md, clazz,
                                                   (longName) ?
                                                   Mangle.Type.METHOD_JNI_LONG :
                                                   Mangle.Type.METHOD_JNI_SHORT));
                    pw.print("  (JNIEnv *, ");
                    List<? extends VariableElement> paramargs = md.getParameters();
                    List<TypeMirror> args = new ArrayList();
                    for (VariableElement p: paramargs) {
                        args.add(types.erasure(p.asType()));
                    }
                    if (md.getModifiers().contains(Modifier.STATIC))
                        pw.print("jclass");
                    else
                        pw.print("jobject");

                    for (TypeMirror arg: args) {
                        pw.print(", ");
                        pw.print(jniType(arg));
                    }
                    pw.println(");" + lineSep);
                }
            }
            pw.println(cppGuardEnd());
            pw.println(guardEnd(cname));
        } catch (TypeSignature.SignatureException e) {
            util.error("jni.sigerror", e.getMessage());
        }
    }


    protected final String jniType(TypeMirror t) throws Util.Exit {
        TypeElement throwable = elems.getTypeElement("java.lang.Throwable");
        TypeElement jClass = elems.getTypeElement("java.lang.Class");
        TypeElement jString = elems.getTypeElement("java.lang.String");
        Element tclassDoc = types.asElement(t);


        switch (t.getKind()) {
            case ARRAY: {
                TypeMirror ct = ((ArrayType) t).getComponentType();
                switch (ct.getKind()) {
                    case BOOLEAN:  return "jbooleanArray";
                    case BYTE:     return "jbyteArray";
                    case CHAR:     return "jcharArray";
                    case SHORT:    return "jshortArray";
                    case INT:      return "jintArray";
                    case LONG:     return "jlongArray";
                    case FLOAT:    return "jfloatArray";
                    case DOUBLE:   return "jdoubleArray";
                    case ARRAY:
                    case DECLARED: return "jobjectArray";
                    default: throw new Error(ct.toString());
                }
            }

            case VOID:     return "void";
            case BOOLEAN:  return "jboolean";
            case BYTE:     return "jbyte";
            case CHAR:     return "jchar";
            case SHORT:    return "jshort";
            case INT:      return "jint";
            case LONG:     return "jlong";
            case FLOAT:    return "jfloat";
            case DOUBLE:   return "jdouble";

            case DECLARED: {
                if (tclassDoc.equals(jString))
                    return "jstring";
                else if (types.isAssignable(t, throwable.asType()))
                    return "jthrowable";
                else if (types.isAssignable(t, jClass.asType()))
                    return "jclass";
                else
                    return "jobject";
            }
        }

        util.bug("jni.unknown.type");
        return null; /* dead code. */
    }
}