java | 易学教程

Race condition occurring during use of Parallel Streams and Atomic Variables

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问题 When the following piece of code is getting executed I am getting exceptions in a random manner. byte[][] loremIpsumContentArray = new byte[64][]; for (int i = 0; i < loremIpsumContentArray.length; i++) { random.nextBytes(loremIpsumContentArray[i] = new byte[CONTENT_SIZE]); } AtomicBoolean aBoolean = new AtomicBoolean(true); List<Long> resultList = IntStream.range(0, 64* 2) .parallel() .mapToObj(i -> getResult(i, aBoolean, repositoryPath, loremIpsumContentArray )) .collect(Collectors.toList()

Cache flush on synchronized entry ,exit and volatile read and write

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问题 When synchronized block execution is completed all the processor cache is flushed or only that object on which synchronized statement acted on will be flushed? In the below example when thread finished execution of method2 does data of obj2 is also flushed to the main memory? class cls1 { int x=10; } class cls2{ int y=10; } class cls3{ cls1 obj1; cls2 obj2; public void method2(){ obj2.y=10; synchronized(obj1){ obj1.x=30; } } public static void main(String[] args) { final cls3 obj3 = new cls3(

How to show Ajax response as modal popup

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问题 I have a link on clicking it is sending ajax request and getting response successfully which is html file and I am appending to a div , but I need to show that div as modal popup and I tried something below. in html file <a th:if="${ratingSummary}" href="#" class="small dark account review_ratings_login">Login to write a review</a> <div id="login_for_review" data-toggle="modal" data-target="#reviewLoginModal"></div> in js file $(document).on('click', '.review_ratings_login', function () { var

设计模式之Prototype(原型)

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? 原型模式定义: 用原型实例指定创建对象的种类,并且通过拷贝这些原型创建新的对象. Prototype模式允许一个对象再创建另外一个可定制的对象，根本无需知道任何如何创建的细节,工作原理是:通过将一个原型对象传给那个要发动创建的对象，这个要发动创建的对象通过请求原型对象拷贝它们自己来实施创建。如何使用? 因为Java中的提供clone()方法来实现对象的克隆,所以Prototype模式实现一下子变得很简单. 以勺子为例： public abstract class AbstractSpoon implements Cloneable { 　　String spoonName; 　　public void setSpoonName(String spoonName) {this.spoonName = spoonName;} 　　public String getSpoonName() {return this.spoonName;} 　　public Object clone() 　　{ 　　　　Object object = null; 　　　　try { 　　　　　　object = super.clone(); 　　　　} catch (CloneNotSupportedException exception) { 　　　　　　System.err.println(

我是培训机构出身的程序员，不敢告诉任何人

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点击上方 SQL数据库开发，关注获取 SQL视频教程 SQL专栏 SQL数据库基础知识汇总 SQL数据库高级知识汇总来源 | InfoQ 作者丨褚杏娟培训机构出身程序员和科班程序员之间，有鄙视链吗？ 1 “谁都看不上培训机构的” “我是培训 + 外包出来的，确实有被甲方嫌弃过。”2016 年从电子信息专业毕业的小右说起这个话题有些落寞。公务员考试失利的小右在大四上学期开始找工作，但因为学习成绩一般，工作找得并不顺利。这个情况持续一段时间后，小右决定去参加某培训机构的 Java 培训。“电子信息专业虽说属于计算机范畴，但其实和编程还不一样的，我也是没办法。”小右很无奈。培训机构的课程对有一定 C、C++ 基础的小右来说还算比较轻松。他所在的那家培训机构的上课内容就是老师带着做做项目，教的代码在后面工作中可以复用。几个月后小右从培训机构毕业，第一份工作是北京当地蛮著名的一个外包机构，薪资 5K。与同批毕业找到不错工作的同学们比，小右还是感到些许心酸。“上课的学费，我是走的贷款。和培训机构签过协议，毕业就可以找到工作。找不到，损失由培训机构承担；找得到，机构每个月要从我的薪资里面抽一部分还学费。“北京的生活成本本来就高，加上机构的抽成，对于刚毕业的小右来说，无疑压力很大。在这家外包公司呆了一年后，小右跳槽了——仍旧是家外包公司。

java tesseract error in linux “Unable to load library 'tesseract': libtesseract.so”

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问题 I am using tess4J ocr library in eclipse and is working fine in my windows. But when i want to run that java program in linux it is giving an error "Unable to load library 'tesseract': libtesseract.so: cannot open shared object file: No such file or directory". I dont have any permissions on linux to install the tesseract or any other software . Just i can use the jar files and run the java program by calling the shell script.Please help me on this . As I am thinking my problem will be solved

How to increase the number of messages consumed by Spring Kafka Consumer in each batch?

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问题 I am building a Kafka Consumer application that consumes messages from a Kafka Topic and performs a database update task. The messages are produced in a large batch once every day - so the Topic has about 1 million messages loaded in 10 minutes. The Topic has 8 partitions. The Spring Kafka Consumer (annotated with @KafkaListener and using a ConcurrentKafkaListenerContainerFactory) is triggered in very short batches. The batch size is sometimes just 1 or 2 messages. It would help performance

MyBatis - One to many - values not set for mapped column

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问题 I am using MyBatis to access the database. For that purpose I have the following classes: class ClassA { private int id; private List<ClassB> list; // public getters and setters } class ClassB { private int id; // public getters and setters } The according DAOs look like that: public interface ClassADAO { @Select("SELECT id, name, description FROM TableA WHERE id = #{id}") @Results( @Result(property = "list", javaType = List.class, column = "id", many = @Many(select = "ClassBDao

Zookeeper系列四：Zookeeper实现分布式锁、Zookeeper实现配置中心

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一、Zookeeper实现分布式锁分布式锁主要用于在分布式环境中保证数据的一致性。包括跨进程、跨机器、跨网络导致共享资源不一致的问题。 1. 分布式锁的实现思路说明：这种实现会有一个缺点，即当有很多进程在等待锁的时候，在释放锁的时候会有很多进程就过来争夺锁，这种现象称为 “惊群效应” 2. 分布式锁优化后的实现思路 3. Zookeeper分布式锁的代码实现准备工作： 1）安装Zookeeper，具体参考我前面的我文章 Zookeeper系列一：Zookeeper介绍、Zookeeper安装配置、ZK Shell的使用 2）新建一个maven项目ZK-Demo,然后在pom.xml里面引入相关的依赖 < dependency > < groupId > com.101tec </ groupId > < artifactId > zkclient </ artifactId > < version > 0.10 </ version > </ dependency > 3.1 Zookeeper分布式锁的核心代码实现实现逻辑参考“ 2. 分布式锁优化后的实现思路 ”中的流程图 package com.study.demo.lock; import java.util.Collections; import java.util.List; import java.util

How to read a rsa public key file in java?

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问题 I have a RSA public key file like this: -----BEGIN RSA PUBLIC KEY----- this is content -----END RSA PUBLIC KEY----- and i use java to read it: KeyFactory factory = KeyFactory.getInstance("RSA"); KeySpec spec = new X509EncodedKeySpec(bytesFromThisFile); // bytesFromThisFile is created and filled correctly PublicKey publicKey = factory.generatePublic(spec); then i get an exception: java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException: invalid key format How to read the

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