小编inv*_*ant的帖子

<property name="hibernateProperties">
  <props>           
    <prop key="hibernate.c3p0.max_size">?</prop>
  </props>
</property>

这只是随机数猜测吗？或者是否有任何研究建议针对特定用例使用特定范围？

我的java类

private static final String constantString = "Constant";    
private static final Integer constantInteger = 5;
public static void main(String[] args) {
    String s2 = constantString + "append"; // LINENUMBER 9
    Integer i2 = constantInteger + 7; // LINENUMBER 10
}

字节码

 LINENUMBER 9 L0
    LDC "Constantappend"
    ASTORE 1
   L1
    LINENUMBER 10 L1
    GETSTATIC TestClass.constantInteger : Ljava/lang/Integer;
    INVOKEVIRTUAL java/lang/Integer.intValue()I
    BIPUSH 7
    IADD

问题1:为什么编译器没有用5代替最终的Integer(constantInteger)值,但是对于String它做了!

如果删除Integer变量的final关键字

java代码:

private static Integer constantInteger = 5;

字节码:

LINENUMBER 10 L1
GETSTATIC TestClass.constantInteger : Ljava/lang/Integer;
INVOKEVIRTUAL java/lang/Integer.intValue()I …

服务器代码:

object EchoService {

  def route: Route = path("ws-echo") {
    get {
      handleWebSocketMessages(flow)
    }
  } ~ path("send-client") {
    get {
      sourceQueue.map(q => {
        println(s"Offering message from server")
        q.offer(BinaryMessage(ByteString("ta ta")))
      } )
      complete("Sent from server successfully")
    }
  }

  val (source, sourceQueue) = {
    val p = Promise[SourceQueue[Message]]
    val s = Source.queue[Message](100, OverflowStrategy.backpressure).mapMaterializedValue(m => {
      p.trySuccess(m)
      m
    })
    (s, p.future)
  }

  val flow =
    Flow.fromSinkAndSourceMat(Sink.ignore, source)(Keep.right)
}

客户代码:

object Client extends App {


  implicit val actorSystem = ActorSystem("akka-system")
  implicit val flowMaterializer = …

我正在使用PreparedStatement更新表

以下代码完美运行

pst = conn.prepareStatement("UPDATE playjdbc SET jlname ='javafx10new' WHERE jfname = 'java10'");
int i = pst.executeUpdate();

但是当我尝试这样的时候它会抛出异常

 pst = conn.prepareStatement("UPDATE playjdbc SET jlname ='javafx10new' WHERE jfname =?");
 pst.setString(2, "java10"); // yeah second column is jfname

 int i = pst.executeUpdate();

堆栈跟踪 :

java.sql.SQLException: Invalid column index
    at oracle.jdbc.driver.OraclePreparedStatement.setStringInternal(OraclePreparedStatement.java:5330)
    at oracle.jdbc.driver.OraclePreparedStatement.setString(OraclePreparedStatement.java:5318)
    at oracle.jdbc.driver.OraclePreparedStatementWrapper.setString(OraclePreparedStatementWrapper.java:282)
    at com.indus.database.EmployeeDTO.updateData(EmployeeDTO.java:114)

我怎么能转换case class到一个Map地方的领域case class成为关键？

例如:

case class Person(name: String, age: Int)

val p = Person("dude", 89)
val map = p.toMap // <-- ???

这样map等于下面的地图:

Map("name" -> "dude", "age" -> 89)

我的 pvc.yaml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: database-disk
  labels:
    stage: production
    name: database
    app: mysql
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi

kubectl apply -f pvc.yaml在microk8s中运行出现以下错误：

验证数据时出错：ValidationData(PersistentVolumeClaim): io.k8s.api.core.v1.PersistenVolumeClaim 中的未知字段“存储”，如果选择忽略这些错误，请使用 --validate=false 关闭验证

编辑：当我在虚拟机上复制文本时存储缩进错误:(，现在工作正常

考虑以下代码:

1. 如何str1在不使用的情况下创建对象new String()？
2. 为什么str1和str2对象引用相同的内存位置？

String str1 = "hello";
String str2 = "hello";