com.facebook.presto.jdbc.internal.jol.info.FieldData Maven / Gradle / Ivy

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 * 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
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package com.facebook.presto.jdbc.internal.jol.info;

import com.facebook.presto.jdbc.internal.jol.util.VMSupport;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

/**
 * Holds the field information, without the layout.
 *
 * @author Aleksey Shipilev
 */
public class FieldData {

    /**
     * Creates the synthetic field data.
     *
     * @param hostKlass class name where the field is declared
     * @param fieldName field name
     * @param fieldType string representation of field type
     * @return field data
     */
    public static FieldData create(String hostKlass, String fieldName, String fieldType) {
        return new FieldData(null, -1, hostKlass, fieldName, fieldType);
    }

    /**
     * Parses the field data from the existing field.
     *
     * @param field field to parse
     * @return field data
     */
    public static FieldData parse(Field field) {
        return new FieldData(field, computeOffset(field), field.getDeclaringClass().getSimpleName(), field.getName(), field.getType().getSimpleName());
    }

    private final String name;
    private final String type;
    private final String klass;
    private final Field refField;
    private final int vmOffset;

    private FieldData(Field refField, int vmOffset, String hostKlass, String fieldName, String fieldType) {
        this.klass = hostKlass;
        this.name = fieldName;
        this.type = fieldType;
        this.refField = refField;
        this.vmOffset = vmOffset;
    }

    private static int computeOffset(Field field) {
        if (Modifier.isStatic(field.getModifiers())) {
            return (int) VMSupport.U.staticFieldOffset(field);
        } else {
            return (int) VMSupport.U.objectFieldOffset(field);
        }
    }

    /**
     * Answers the class for the field type
     *
     * @return string representation of field type
     */
    public String typeClass() {
        return type;
    }

    /**
     * Answers the class for the field holder.
     *
     * @return string representation of holder class
     */
    public String hostClass() {
        return klass;
    }

    /**
     * Answers the field name.
     *
     * @return field name
     */
    public String name() {
        return name;
    }

    /**
     * Gets the string representation of field value,
     * if appropriate.
     *
     * @param object the object to read the contents from
     * @return field value in given object
     */
    public String safeValue(Object object) {
        if (refField != null) {
            try {
                return VMSupport.safeToString(refField.get(object));
            } catch (IllegalAccessException iae) {
                // exception, try again
            }

            try {
                refField.setAccessible(true);
                return VMSupport.safeToString(refField.get(object));
            } catch (Exception e) {
                return "(access denied)";
            }
        } else {
            return "N/A";
        }
    }

    /**
     * The VM offset for the field, as discovered.
     * Some layouters need to know this.
     *
     * @return vm offset
     */
    public int vmOffset() {
        if (vmOffset != -1) {
            return vmOffset;
        } else {
            throw new IllegalStateException("VM offset is not defined");
        }
    }

}