首先，创建一个实体类Order对象，代码如下：
public class Order{
private String orderNo;
private String name;
public Order(){
setOrderNo("order:"+ UUID.randomUUID().toString());
setName("name:"+UUID.randomUUID().toString());
}
public String getOrderNo() {
return orderNo;
}
public void setOrderNo(String orderNo) {
this.orderNo = orderNo;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
第一个 方法，使用for循环遍历查找，即使找到也不做任何事，代码片段如下：
private static void test2(){
List<Order> orderList=new ArrayList<>();
for (int i=0;i<1000;i++){
orderList.add(new Order());
}
System.out.println("aaaaa");
boolean flag=true;
AtomicLong atomicLong=new AtomicLong(0);
do {
//遍历
for (Order order:orderList){
if (order.getName().equals("abc")){
//find but do nothing
Optional.of(order);
}
}
//orderList.stream().filter(order -> order.getName().equals("abc")).findFirst();
long value=atomicLong.incrementAndGet();
if (value>10000L){
System.out.println("推出");
flag=false;
}
}while (flag);
}
第二个方法，使用java8中的lambda表达式stream中的filter进行查找,代码如下：
private static void test1(){
List<Order> orderList=new ArrayList<>();
for (int i=0;i<1000;i++){
orderList.add(new Order());
}
System.out.println("aaaaa");
boolean flag=true;
AtomicLong atomicLong=new AtomicLong(0);
do {
//遍历
orderList.stream().filter(order -> order.getName().equals("abc")).findFirst();
long value=atomicLong.incrementAndGet();
if (value>10000L){
System.out.println("推出");
flag=false;
}
}while (flag);
}
两段代码如果不设置java的Xmx参数，都能正常运行，假设设置参数
java -Xmx2m
那么第二段使用java8的lambda表达式的程序将会报错，抛出异常
Exception in thread "main" java.lang.InternalError: zero_L=Lambda(a0:L)=>{
t1:L=LambdaForm.identity_L((null));t1:L}
at java.lang.invoke.MethodHandleStatics.newInternalError(MethodHandleStatics.java:127)
at java.lang.invoke.LambdaForm.compileToBytecode(LambdaForm.java:660)
at java.lang.invoke.LambdaForm.prepare(LambdaForm.java:635)
at java.lang.invoke.MethodHandle.<init>(MethodHandle.java:461)
at java.lang.invoke.BoundMethodHandle.<init>(BoundMethodHandle.java:58)
at java.lang.invoke.SimpleMethodHandle.<init>(SimpleMethodHandle.java:37)
at java.lang.invoke.SimpleMethodHandle.make(SimpleMethodHandle.java:41)
at java.lang.invoke.LambdaForm.createIdentityForms(LambdaForm.java:1783)
at java.lang.invoke.LambdaForm.<clinit>(LambdaForm.java:1833)
at java.lang.invoke.DirectMethodHandle.makePreparedLambdaForm(DirectMethodHandle.java:222)
at java.lang.invoke.DirectMethodHandle.preparedLambdaForm(DirectMethodHandle.java:187)
at java.lang.invoke.DirectMethodHandle.preparedLambdaForm(DirectMethodHandle.java:176)
at java.lang.invoke.DirectMethodHandle.make(DirectMethodHandle.java:83)
at java.lang.invoke.MethodHandles$Lookup.getDirectMethodCommon(MethodHandles.java:1655)
at java.lang.invoke.MethodHandles$Lookup.getDirectMethodNoSecurityManager(MethodHandles.java:1612)
at java.lang.invoke.MethodHandles$Lookup.getDirectMethodForConstant(MethodHandles.java:1797)
at java.lang.invoke.MethodHandles$Lookup.linkMethodHandleConstant(MethodHandles.java:1746)
at java.lang.invoke.MethodHandleNatives.linkMethodHandleConstant(MethodHandleNatives.java:477)
at com.github.xiaoymin.Java8Test.test1(Java8Test.java:63)
at com.github.xiaoymin.Java8Test.main(Java8Test.java:24)
Caused by: java.lang.OutOfMemoryError: GC overhead limit exceeded
at jdk.internal.org.objectweb.asm.ByteVector.<init>(ByteVector.java:84)
at jdk.internal.org.objectweb.asm.MethodWriter.visitAnnotation(MethodWriter.java:555)
at java.lang.invoke.InvokerBytecodeGenerator.generateCustomizedCodeBytes(InvokerBytecodeGenerator.java:640)
at java.lang.invoke.InvokerBytecodeGenerator.generateCustomizedCode(InvokerBytecodeGenerator.java:618)
at java.lang.invoke.LambdaForm.compileToBytecode(LambdaForm.java:654)
... 18 more
*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message can't create byte arrau at JPLISAgent.c line: 813
*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message can't create byte arrau at JPLISAgent.c line: 813
*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message can't create byte arrau at JPLISAgent.c line: 813
那么，是否可以认为在超过2层的for循环中，对于集合的筛选或者等其他各种操作，应该禁用java8的stream操作？
因为一旦外层for循环次数较多，java8中的stream操作将会创造很多临时对象，必然导致JVM频繁的GC操作！！
