openjdk jol 工具打印 Java 对象内存布局

淡淡的烟草味﹌ 2022-10-27 01:38 271阅读 0赞

1、maven 依赖

<dependency>
    	<groupId>org.openjdk.jol</groupId>
    	<artifactId>jol-core</artifactId>
    	<version>0.10</version>
    </dependency>

2、测试类

package constxiong;
    
    import org.openjdk.jol.info.ClassLayout;
    import org.openjdk.jol.info.GraphLayout;
    
    /**
     * 测试对象占用的内存信息
     */
    public class TestObjectSize {
    
        public static void main(String[] args) {
            System.out.println("对象内部信息");
            System.out.println(ClassLayout.parseInstance(new String("ConstXiong")).toPrintable());
            System.out.println(ClassLayout.parseInstance(new char[]{'C', 'o', 'n', 's', 't', 'X', 'i', 'o', 'n', 'g'}).toPrintable());
    
            System.out.println("对象整体信息");
            System.out.println(GraphLayout.parseInstance(new String("ConstXiong")).toPrintable());
            System.out.println(GraphLayout.parseInstance(new char[]{'C', 'o', 'n', 's', 't', 'X', 'i', 'o', 'n', 'g'}).toPrintable());
    
            System.out.println("对象占用总空间");
            System.out.println(GraphLayout.parseInstance(new String("ConstXiong")).totalSize());
            System.out.println(GraphLayout.parseInstance(new char[]{'C', 'o', 'n', 's', 't', 'X', 'i', 'o', 'n', 'g'}).totalSize());
        }
    }

3、打印结果

对象内部信息
    java.lang.String object internals:
     OFFSET  SIZE     TYPE DESCRIPTION                               VALUE
          0     4          (object header)                           01 00 00 00 (00000001 00000000 00000000 00000000) (1)
          4     4          (object header)                           00 00 00 00 (00000000 00000000 00000000 00000000) (0)
          8     4          (object header)                           d0 16 3e 17 (11010000 00010110 00111110 00010111) (389945040)
         12     4   char[] String.value                              [C, o, n, s, t, X, i, o, n, g]
         16     4      int String.hash                               0
         20     4          (loss due to the next object alignment)
    Instance size: 24 bytes
    Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
    
    [C object internals:
     OFFSET  SIZE   TYPE DESCRIPTION                               VALUE
          0     4        (object header)                           01 00 00 00 (00000001 00000000 00000000 00000000) (1)
          4     4        (object header)                           00 00 00 00 (00000000 00000000 00000000 00000000) (0)
          8     4        (object header)                           08 02 3e 17 (00001000 00000010 00111110 00010111) (389939720)
         12     4        (object header)                           0a 00 00 00 (00001010 00000000 00000000 00000000) (10)
         16    20   char [C.<elements>                             N/A
         36     4        (loss due to the next object alignment)
    Instance size: 40 bytes
    Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
    
    
    对象整体信息
    java.lang.String@1a93a7cad object externals:
              ADDRESS       SIZE TYPE             PATH                           VALUE
             d6284f40         40 [C               .value                         [C, o, n, s, t, X, i, o, n, g]
             d6284f68   11751072 (something else) (somewhere else)               (something else)
             d6db9e08         24 java.lang.String                                (object)
    
    
    [C@3b764bced object externals:
              ADDRESS       SIZE TYPE PATH                           VALUE
             d6df9610         40 [C                                  [C, o, n, s, t, X, i, o, n, g]
    
    
    
    对象占用总空间
    64
    40

内存分析：

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