# java 中错误总结

# rocketMq

# 与 springboot 兼容问题

An attempt was made to call a method that does not exist. The attempt was made from the following location:
com.alibaba.cloud.stream.binder.rocketmq.RocketMQMessageChannelBinder.createProducerMessageHandler(RocketMQMessageChannelBinder.java:172)

The following method did not exist:
org.springframework.integration.channel.AbstractMessageChannel.getChannelInterceptors()Ljava/util/List;

The method's class, org.springframework.integration.channel.AbstractMessageChannel, is available from the following locations:
jar:file:/C:/Users/admin/.gradle/caches/modules-2/files-2.1/org.springframework.integration/spring-integration-core/5.3.2.RELEASE/1f44e4fc3209233fe4ab75934c3ab151eb88474f/spring-integration-core-5.3.2.RELEASE.jar!/org/springframework/integration/channel/AbstractMessageChannel.class

The class hierarchy was loaded from the following locations:
org.springframework.integration.channel.AbstractMessageChannel: file:/C:/Users/admin/.gradle/caches/modules-2/files-2.1/org.springframework.integration/spring-integration-core/5.3.2.RELEASE/1f44e4fc3209233fe4ab75934c3ab151eb88474f/spring-integration-core-5.3.2.RELEASE.jar
org.springframework.integration.context.IntegrationObjectSupport: file:/C:/Users/admin/.gradle/caches/modules-2/files-2.1/org.springframework.integration/spring-integration-core/5.3.2.RELEASE/1f44e4fc3209233fe4ab75934c3ab151eb88474f/spring-integration-core-5.3.2.RELEASE.jar

Action:
Correct the classpath of your application so that it contains a single, compatible version of org.springframework.integration.channel.AbstractMessageChannel

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版本匹配

rocketMq 用的2.几，那么 springboot 也就只能 2.几；
不能出现 rocketMq 用的 2.2.0，而 springboot 用的 2.3 及其以上

# java 开发常犯的 10 个错误

返回顶部

# 1、Array 转 ArrayList

不再赘述

# 2、判断一个数组是否包含某个值

Arrays.asList(arr).contains(targetValue);

# 3、在循环内部删除 List 中的一个元素

ArrayList<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c","d"));
for (int i = 0; i < list.size(); i++) {
    list.remove(i);
}
System.out.println(list);

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ArrayList<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c","d"));
for (String s : list) {
    if (s.equals("a")){
    list.remove(s);
    }
}

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上面会抛出ConcurrentModificationException异常。

然而接下来的代码却是 OK 的：

ArrayList<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c","d"));
Iterator<String> iter = list.iterator();
while (iter.hasNext()) {
String s = iter.next();
    if (s.equals("a")) {
        iter.remove();
    }
}

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下面的代码也不会有问题CopyOnWriteArrayList

List<String> list = new CopyOnWriteArrayList<>();
for (String s : list) {
    list.remove(s);

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next()方法需要在remove()方法之前被调用，在 foreach 循环里，编译器会在删除元素操作后调用 next 方法，这导致了 ConcurrentModificationException 异常。更多详细信息，可以查看 ArrayList.iterator()的源码。

当然 java8 中也已经新增如下方法，很好用：

resultList.removeIf(treeVo -> blankBuildingsCompanyIds.contains(treeVo.getId()));

# 4、HashTable 与 HashMap

# 6、访问级别

开发人员经常使用 public 修饰类字段，虽然这很容易让别人直接通过引用获取该字段的值，但这是一个不好的设计。根据经验，应该尽可能的降低成员属性的访问级别。

# 7、ArrayList 和 LinkedList

为什么开发人员经常使用 ArrayList 和 LinkedList，却不知道他们之间的区别，因为它们看起来很像。然而它们之间有着巨大的性能差异。简单的说，如果有大量的增加删除操作并且没有很多的随机访问元素的操作，应该首选 LinkedList。

# 9、父类和子类的构造方法

是因为父类的默认构造方法未定义。在 Java 中，如果一个类没有定义构造方法，编译器会默认插入一个无参数的构造方法；但是如果一个构造方法在父类中已定义，在这种情况，编译器是不会自动插入一个默认的无参构造方法，

# 前端下载文件

Could not find acceptable representation

只需将接口返回类型改为void

# 异常排查

# java.lang.IllegalArgumentException:Input == null

缺少文件路径，或者路径不对

# Netty

# Netty作为客户端

ws://es.sunshy.cn:8089?userGuid=20210813095117260_9f46d7f0bdec4c3fb934a0391b4b811c&onlineGuid=fd17b0b268dc45b9b7d6316a1be4bc73&token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJVc2VyR3VpZCI6IjIwMjEwODEzMDk1MTE3MjYwXzlmNDZkN2YwYmRlYzRjM2ZiOTM0YTAzOTFiNGI4MTFjIiwiVXNlck5hbWUiOiLmtYvor5UwODEyIiwiUm9sZUNvZGUiOiI5OSIsIk9ubGluZUd1aWQiOiJmZDE3YjBiMjY4ZGM0NWI5YjdkNjMxNmExYmU0YmM3MyIsIm5iZiI6MTYyODgzODgyNywiZXhwIjoxNjI4ODQyNDI3LCJpc3MiOiJHZWxhbmRlIiwiYXVkIjoiR0VTTVAifQ.QdhcrwgwAozp3H_ZZGJF1yIukQIfHDaLRewZlxCIOyE&subscribe=true

在netty中，这个请求这个地址，服务器会报400【400 Bad Request】错误，原因就是地址的问题，在问号【?】的前面必须是【/】即地址为：

ws://es.sunshy.cn:8089/?userGuid=20210813095117260_9f46d7f0bdec4c3fb934a0391b4b811c&onlineGuid=fd17b0b268dc45b9b7d6316a1be4bc73&token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJVc2VyR3VpZCI6IjIwMjEwODEzMDk1MTE3MjYwXzlmNDZkN2YwYmRlYzRjM2ZiOTM0YTAzOTFiNGI4MTFjIiwiVXNlck5hbWUiOiLmtYvor5UwODEyIiwiUm9sZUNvZGUiOiI5OSIsIk9ubGluZUd1aWQiOiJmZDE3YjBiMjY4ZGM0NWI5YjdkNjMxNmExYmU0YmM3MyIsIm5iZiI6MTYyODgzODgyNywiZXhwIjoxNjI4ODQyNDI3LCJpc3MiOiJHZWxhbmRlIiwiYXVkIjoiR0VTTVAifQ.QdhcrwgwAozp3H_ZZGJF1yIukQIfHDaLRewZlxCIOyE&subscribe=true

以下为stackoverflow的解释：

wss://domain?access_token...is not a valid URL. The path component must start with a / and not a ?. This means that the request is invalid which can explain the response of 400 Bad Request.

The URL must be at least wss://domain/?access_token... (i.e. a / before the ?) but maybe the rest of the URL is unexpected by the server too. Please check the actual requirements of the server.