计算java对象的内存占用

代码引用自：https://blog.csdn.net/antony9118/article/details/54317637  感谢博主分享：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

/**
 * This class contains object info generated by ClassIntrospector tool
 */
public class ObjectInfo {
    /** Field name */
    public final String name;
    /** Field type name */
    public final String type;
    /** Field data formatted as string */
    public final String contents;
    /** Field offset from the start of parent object */
    public final int offset;
    /** Memory occupied by this field */
    public final int length;
    /** Offset of the first cell in the array */
    public final int arrayBase;
    /** Size of a cell in the array */
    public final int arrayElementSize;
    /** Memory occupied by underlying array (shallow), if this is array type */
    public final int arraySize;
    /** This object fields */
    public final List<ObjectInfo> children;

    public ObjectInfo(String name, String type, String contents, int offset, int length, int arraySize,
                      int arrayBase, int arrayElementSize) {
        this.name = name;
        this.type = type;
        this.contents = contents;
        this.offset = offset;
        this.length = length;
        this.arraySize = arraySize;
        this.arrayBase = arrayBase;
        this.arrayElementSize = arrayElementSize;
        children = new ArrayList<ObjectInfo>(1);
    }

    public void addChild(final ObjectInfo info) {
        if (info != null) {
            children.add(info);
        }
    }

    /**
     * Get the full amount of memory occupied by a given object. This value may be slightly less than
     * an actual value because we don't worry about memory alignment - possible padding after the last object field.
     *
     * The result is equal to the last field offset + last field length + all array sizes + all child objects deep sizes
     *
     * @return Deep object size
     */
    public long getDeepSize() {
        //return length + arraySize + getUnderlyingSize( arraySize != 0 );
        return addPaddingSize(arraySize + getUnderlyingSize(arraySize != 0));
    }

    long size = 0;

    private long getUnderlyingSize(final boolean isArray) {
        //long size = 0;
        for (final ObjectInfo child : children)
            size += child.arraySize + child.getUnderlyingSize(child.arraySize != 0);
        if (!isArray && !children.isEmpty()) {
            int tempSize = children.get(children.size() - 1).offset + children.get(children.size() - 1).length;
            size += addPaddingSize(tempSize);
        }

        return size;
    }

    private static final class OffsetComparator implements Comparator<ObjectInfo> {
        @Override
        public int compare(final ObjectInfo o1, final ObjectInfo o2) {
            return o1.offset - o2.offset; //safe because offsets are small non-negative numbers
        }
    }

    //sort all children by their offset
    public void sort() {
        Collections.sort(children, new OffsetComparator());
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder();
        toStringHelper(sb, 0);
        return sb.toString();
    }

    private void toStringHelper(final StringBuilder sb, final int depth) {
        depth(sb, depth).append("name=").append(name).append(", type=").append(type)
                .append(", contents=").append(contents).append(", offset=").append(offset)
                .append(", length=").append(length);
        if (arraySize > 0) {
            sb.append(", arrayBase=").append(arrayBase);
            sb.append(", arrayElemSize=").append(arrayElementSize);
            sb.append(", arraySize=").append(arraySize);
        }
        for (final ObjectInfo child : children) {
            sb.append('
');
            child.toStringHelper(sb, depth + 1);
        }
    }

    private StringBuilder depth(final StringBuilder sb, final int depth) {
        for (int i = 0; i < depth; ++i)
            sb.append("	");
        return sb;
    }

    private long addPaddingSize(long size) {
        if (size % 8 != 0) {
            return (size / 8 + 1) * 8;
        }
        return size;
    }

}

import java.lang.reflect.Array;
import java.lang.reflect.Field;  
import java.lang.reflect.Modifier;  
import java.util.ArrayList;  
import java.util.Arrays;  
import java.util.Collections;  
import java.util.HashMap;  
import java.util.IdentityHashMap;  
import java.util.List;  
import java.util.Map;  

import sun.misc.Unsafe;  

/** 
 * This class could be used for any object contents/memory layout printing. 
 */  
public class ClassIntrospector {  

    private static final Unsafe unsafe;  
    /** Size of any Object reference */  
    private static final int objectRefSize;  
    static {  
        try {  
            Field field = Unsafe.class.getDeclaredField("theUnsafe");  
            field.setAccessible(true);  
            unsafe = (Unsafe) field.get(null);  

            objectRefSize = unsafe.arrayIndexScale(Object[].class);  
        } catch (Exception e) {  
            throw new RuntimeException(e);  
        }  
    }  

    /** Sizes of all primitive values */  
    private static final Map<Class, Integer> primitiveSizes;  

    static {  
        primitiveSizes = new HashMap<Class, Integer>(10);  
        primitiveSizes.put(byte.class, 1);  
        primitiveSizes.put(char.class, 2);  
        primitiveSizes.put(int.class, 4);  
        primitiveSizes.put(long.class, 8);  
        primitiveSizes.put(float.class, 4);  
        primitiveSizes.put(double.class, 8);  
        primitiveSizes.put(boolean.class, 1);  
    }  

    /** 
     * Get object information for any Java object. Do not pass primitives to 
     * this method because they will boxed and the information you will get will 
     * be related to a boxed version of your value. 
     *  
     * @param obj 
     *            Object to introspect 
     * @return Object info 
     * @throws IllegalAccessException 
     */  
    public ObjectInfo introspect(final Object obj)  
            throws IllegalAccessException {  
        try {  
            return introspect(obj, null);  
        } finally { // clean visited cache before returning in order to make  
                    // this object reusable  
            m_visited.clear();  
        }  
    }  

    // we need to keep track of already visited objects in order to support  
    // cycles in the object graphs  
    private IdentityHashMap<Object, Boolean> m_visited = new IdentityHashMap<Object, Boolean>(  
            100);  

    private ObjectInfo introspect(final Object obj, final Field fld)  
            throws IllegalAccessException {  
        // use Field type only if the field contains null. In this case we will  
        // at least know what's expected to be  
        // stored in this field. Otherwise, if a field has interface type, we  
        // won't see what's really stored in it.  
        // Besides, we should be careful about primitives, because they are  
        // passed as boxed values in this method  
        // (first arg is object) - for them we should still rely on the field  
        // type.  
        boolean isPrimitive = fld != null && fld.getType().isPrimitive();  
        boolean isRecursive = false; // will be set to true if we have already  
                                        // seen this object  
        if (!isPrimitive) {
            if (m_visited.containsKey(obj)) {
                isRecursive = true;
            }
            m_visited.put(obj, true);  
        }  

        final Class type = (fld == null || (obj != null && !isPrimitive)) ? obj  
                .getClass() : fld.getType();  
        int arraySize = 0;  
        int baseOffset = 0;  
        int indexScale = 0;  
        if (type.isArray() && obj != null) {  
            baseOffset = unsafe.arrayBaseOffset(type);  
            indexScale = unsafe.arrayIndexScale(type);  
            arraySize = baseOffset + indexScale * Array.getLength(obj);  
        }  

        final ObjectInfo root;  
        if (fld == null) {  
            root = new ObjectInfo("", type.getCanonicalName(), getContents(obj,  
                    type), 0, getShallowSize(type), arraySize, baseOffset,  
                    indexScale);  
        } else {  
            final int offset = (int) unsafe.objectFieldOffset(fld);  
            root = new ObjectInfo(fld.getName(), type.getCanonicalName(),  
                    getContents(obj, type), offset, getShallowSize(type),  
                    arraySize, baseOffset, indexScale);  
        }  

        if (!isRecursive && obj != null) {  
            if (isObjectArray(type)) {  
                // introspect object arrays  
                final Object[] ar = (Object[]) obj;  
                for (final Object item : ar)
                    if (item != null) {
                        root.addChild(introspect(item, null));
                    }
            } else {  
                for (final Field field : getAllFields(type)) {  
                    if ((field.getModifiers() & Modifier.STATIC) != 0) {  
                        continue;  
                    }  
                    field.setAccessible(true);  
                    root.addChild(introspect(field.get(obj), field));  
                }  
            }  
        }  

        root.sort(); // sort by offset  
        return root;  
    }  

    // get all fields for this class, including all superclasses fields  
    private static List<Field> getAllFields(final Class type) {
        if (type.isPrimitive()) {
            return Collections.emptyList();
        }
        Class cur = type;  
        final List<Field> res = new ArrayList<Field>(10);  
        while (true) {  
            Collections.addAll(res, cur.getDeclaredFields());
            if (cur == Object.class) {
                break;
            }
            cur = cur.getSuperclass();  
        }  
        return res;  
    }  

    // check if it is an array of objects. I suspect there must be a more  
    // API-friendly way to make this check.  
    private static boolean isObjectArray(final Class type) {
        if (!type.isArray()) {
            return false;
        }
        if (type == byte[].class || type == boolean[].class
                || type == char[].class || type == short[].class
                || type == int[].class || type == long[].class
                || type == float[].class || type == double[].class) {
            return false;
        }
        return true;  
    }  

    // advanced toString logic  
    private static String getContents(final Object val, final Class type) {
        if (val == null) {
            return "null";
        }
        if (type.isArray()) {
            if (type == byte[].class) {
                return Arrays.toString((byte[]) val);
            } else if (type == boolean[].class) {
                return Arrays.toString((boolean[]) val);
            } else if (type == char[].class) {
                return Arrays.toString((char[]) val);
            } else if (type == short[].class) {
                return Arrays.toString((short[]) val);
            } else if (type == int[].class) {
                return Arrays.toString((int[]) val);
            } else if (type == long[].class) {
                return Arrays.toString((long[]) val);
            } else if (type == float[].class) {
                return Arrays.toString((float[]) val);
            } else if (type == double[].class) {
                return Arrays.toString((double[]) val);
            } else {
                return Arrays.toString((Object[]) val);
            }
        }  
        return val.toString();  
    }  

    // obtain a shallow size of a field of given class (primitive or object  
    // reference size)  
    private static int getShallowSize(final Class type) {
        if (type.isPrimitive()) {
            final Integer res = primitiveSizes.get(type);
            return res != null ? res : 0;
        } else {
            return objectRefSize;
        }
    }  
}  

 使用：

        final ClassIntrospector ci = new ClassIntrospector();

　　　　 ObjectInfo res;
        System.out.println("int:" + ci.introspect(new Integer(2)).getDeepSize());
        System.out.println("str3:" + ci.introspect("abcd").getDeepSize());

        res = ci.introspect(new ObjectA());
        System.out.println("ObjectA:" + res.getDeepSize());    

其中  ObjectA：

private static class ObjectA {
        String str;  // 4
        int i1; // 4
        byte b1; // 1
        byte b2; // 1
        int i2;  // 4
        byte b3;  // 1
        ObjectB obj; //4
    }

    private static class ObjectB {

    }