本文使用的JDK版本：
$ java -version java version "1.8.0_261" Java(TM) SE Runtime Environment (build 1.8.0_261-b12) Java HotSpot(TM) 64-Bit Server VM (build 25.261-b12, mixed mode)
1.
代码文件 GCLogAnalysis.java
import java.util.Random;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.LongAdder;
public class GCLogAnalysis {
private static Random random = new Random();
public static void main(String[] args) {
// 当前毫秒时间戳
long startMillis = System.currentTimeMillis();
// 持续运行毫秒数; 可根据需要进行修改
long timeoutMillis = TimeUnit.SECONDS.toMillis(1);
// 结束时间戳
long endMillis = startMillis + timeoutMillis;
LongAdder counter = new LongAdder();
System.out.println("正在执行...");
// 缓存一部分对象; 进入老年代
int cacheSize = 2000;
Object[] cachedGarbage = new Object[cacheSize];
// 在此时间范围内,持续循环
while (System.currentTimeMillis() < endMillis) {
// 生成垃圾对象
Object garbage = generateGarbage(100*1024);
counter.increment();
int randomIndex = random.nextInt(2 * cacheSize);
if (randomIndex < cacheSize) {
cachedGarbage[randomIndex] = garbage;
}
}
System.out.println("执行结束!共生成对象次数:" + counter.longValue());
}
// 生成对象
private static Object generateGarbage(int max) {
int randomSize = random.nextInt(max);
int type = randomSize % 4;
Object result = null;
switch (type) {
case 0:
result = new int[randomSize];
break;
case 1:
result = new byte[randomSize];
break;
case 2:
result = new double[randomSize];
break;
default:
StringBuilder builder = new StringBuilder();
String randomString = "randomString-Anything";
while (builder.length() < randomSize) {
builder.append(randomString);
builder.append(max);
builder.append(randomSize);
}
result = builder.toString();
break;
}
return result;
}
}
首先在terminal中编译一下此文件
javac GCLogAnalysis.java
如果有乱码报错无法编译，可以加字符集参数
javac -encoding UTF-8 GCLogAnalysis.java
编译完成之后会生成一个 GCLogAnalysis.class文件
执行 命令：
$ java -XX:+PrintGCDetails GCLogAnalysis
$ java -XX:+PrintGCDetails GCLogAnalysis 正在执行... [GC (Allocation Failure) [PSYoungGen: 49139K->8189K(57344K)] 49139K->16650K(188416K), 0.0070231 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] [GC (Allocation Failure) [PSYoungGen: 57305K->8176K(106496K)] 65766K->34377K(237568K), 0.0159032 secs] [Times: user=0.02 sys=0.00, real=0.02 secs] [GC (Allocation Failure) [PSYoungGen: 106480K->8190K(106496K)] 132681K->69927K(237568K), 0.0229538 secs] [Times: user=0.03 sys=0.01, real=0.02 secs] [GC (Allocation Failure) [PSYoungGen: 106020K->8178K(204800K)] 167757K->103995K(335872K), 0.0203049 secs] [Times: user=0.00 sys=0.03, real=0.02 secs] [Full GC (Ergonomics) [PSYoungGen: 8178K->0K(204800K)] [ParOldGen: 95817K->97054K(201728K)] 103995K->97054K(406528K), [metaspace: 2678K->2678K(1056768K)], 0.0266877 secs] [Times: user=0.06 sys=0.00, real=0.03 secs] [GC (Allocation Failure) [PSYoungGen: 196608K->8189K(204800K)] 293662K->156047K(406528K), 0.0251842 secs] [Times: user=0.08 sys=0.05, real=0.02 secs] [Full GC (Ergonomics) [PSYoungGen: 8189K->0K(204800K)] [ParOldGen: 147858K->138866K(278016K)] 156047K->138866K(482816K), [metaspace: 2678K->2678K(1056768K)], 0.0366620 secs] [Times: user=0.11 sys=0.00, real=0.04 secs] [GC (Allocation Failure) [PSYoungGen: 196420K->62379K(387072K)] 335287K->201245K(665088K), 0.0281210 secs] [Times: user=0.02 sys=0.08, real=0.03 secs] [GC (Allocation Failure) [PSYoungGen: 386987K->77822K(408064K)] 525853K->284071K(686080K), 0.0570028 secs] [Times: user=0.03 sys=0.13, real=0.06 secs] [Full GC (Ergonomics) [PSYoungGen: 77822K->0K(408064K)] [ParOldGen: 206249K->230046K(398848K)] 284071K->230046K(806912K), [metaspace: 2678K->2678K(1056768K)], 0.0563328 secs] [Times: user=0.11 sys=0.05, real=0.06 secs] [GC (Allocation Failure) [PSYoungGen: 330240K->102088K(648704K)] 560286K->332134K(1047552K), 0.0484569 secs] [Times: user=0.06 sys=0.13, real=0.05 secs] 执行结束!共生成对象次数:5949 Heap PSYoungGen total 648704K, used 361282K [0x0000000780900000, 0x00000007b2500000, 0x00000007c0000000) eden space 524288K, 49% used [0x0000000780900000,0x000000079061e6b0,0x00000007a0900000) from space 124416K, 82% used [0x00000007a8e80000,0x00000007af232278,0x00000007b0800000) to space 136704K, 0% used [0x00000007a0900000,0x00000007a0900000,0x00000007a8e80000) ParOldGen total 398848K, used 230046K [0x0000000701a00000, 0x0000000719f80000, 0x0000000780900000) object space 398848K, 57% used [0x0000000701a00000,0x000000070faa7940,0x0000000719f80000) metaspace used 2684K, capacity 4486K, committed 4864K, reserved 1056768K class space used 287K, capacity 386K, committed 512K, reserved 1048576K
从输出的内容中可以看到GC的次数和类型等详细信息。
新版本的java有些参数废弃了，见注：
注： 一些常见的即将废弃的jvm参数说明 转自https://python.iitter.com/other/114258.html jdk1.8.0_171，在应用启动的时候，配置如下jvm参数，会出现警告信息 1. -XX:+UseFastAccessorMethods 含义：get,set 方法转成本地代码（对于jvm来说是冗余代码，jvm将进行优化） 说明： UseFastAccessorMethods option is harmful and has been removed in JDK 9. You need to delete this option from run configuration. 2. -XX:+UseConcMarkSweepGC 含义： 使用CMS GC，默认新生代会使用ParNew 说明：Option UseConcMarkSweepGC was deprecated in version 9.0 and will likely be removed in a future release. 3.-XX:+PrintGCDetails 含义：GC回收信息详解 说明：-XX:+PrintGCDetails is deprecated. Will use -Xlog:gc* instead.，即需要配置成这样：-Xlog:gc:gc.log 4.-XX:+PrintGCDateStamps 含义：把gc日志带上时间戳 说明：Unrecognized VM option ‘PrintGCDateStamps’
