安装 babel-plugin-transform-remove-consol

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npm install babel-plugin-transform-remove-console --save-dev

修改 babel.config.js 文件，加入 plugin transform-remove-console

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module.exports = {
  plugins: ["transform-remove-console"] 
};

这是再运行项目就不会有console输出了，但是我们期望的是 development 环境有，production 环境没有，可以这样设置：

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var babelconfig = {
  presets: ["@vue/cli-plugin-babel/preset"], //其它原有设置
  plugins: []
};
if (process.env.NODE_ENV === "production") {
  // production 环境则增加此插件
  babelconfig.plugins.push("transform-remove-console");
}

module.exports = babelconfig;

这样就可以了。

异常 I

spring cloud 的 eureka server 启动时出现如下错误

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09:17:44.673 [SpringContextShutdownHook] WARN  c.n.d.s.t.d.RetryableEurekaHttpClient - Request execution failed with message: java.net.ConnectException: Connection refused (Connection refused)
09:17:44.674 [SpringContextShutdownHook] ERROR c.netflix.discovery.DiscoveryClient - DiscoveryClient_REGISTER-SERVER/192.168.123.121:register-server:8012 - de-registration failedCannot execute request on any known server
com.netflix.discovery.shared.transport.TransportException: Cannot execute request on any known server
	at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:112)
	at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.cancel(EurekaHttpClientDecorator.java:71)
	at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$2.execute(EurekaHttpClientDecorator.java:74)
	at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77)
	at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.cancel(EurekaHttpClientDecorator.java:71)
	at com.netflix.discovery.DiscoveryClient.unregister(DiscoveryClient.java:941)
	at com.netflix.discovery.DiscoveryClient.shutdown(DiscoveryClient.java:919)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleElement.invoke(InitDestroyAnnotationBeanPostProcessor.java:389)
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleMetadata.invokeDestroyMethods(InitDestroyAnnotationBeanPostProcessor.java:347)
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessBeforeDestruction(InitDestroyAnnotationBeanPostProcessor.java:177)
	at org.springframework.beans.factory.support.DisposableBeanAdapter.destroy(DisposableBeanAdapter.java:242)
	at org.springframework.beans.factory.support.DisposableBeanAdapter.run(DisposableBeanAdapter.java:235)
	at org.springframework.cloud.context.scope.GenericScope$BeanLifecycleWrapper.destroy(GenericScope.java:403)
	at org.springframework.cloud.context.scope.GenericScope.destroy(GenericScope.java:142)
	at org.springframework.beans.factory.support.DisposableBeanAdapter.destroy(DisposableBeanAdapter.java:258)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroyBean(DefaultSingletonBeanRegistry.java:571)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingleton(DefaultSingletonBeanRegistry.java:543)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingleton(DefaultListableBeanFactory.java:1072)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingletons(DefaultSingletonBeanRegistry.java:504)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingletons(DefaultListableBeanFactory.java:1065)
	at org.springframework.context.support.AbstractApplicationContext.destroyBeans(AbstractApplicationContext.java:1060)
	at org.springframework.context.support.AbstractApplicationContext.doClose(AbstractApplicationContext.java:1029)
	at org.springframework.context.support.AbstractApplicationContext$1.run(AbstractApplicationContext.java:948)

这个错误是由于 Eureka 启动时默认会把自己注册到注册中心（默认注册中心是localhost，虽然没配置，但是有这么个默认值），而此时没有注册中心（自己是注册中心，尚未启动），所以出错了。

解决方案很简单，禁止注册就好了

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eureka:
  instance:
    preferIpAddress: true
  client:
    register-with-eureka: false
    fetch-registry: false

如果网络上已经有注册中心，也可以提供注册中心的URL，让 eureka server 能购找到注册中心也可

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eureka:
  client:
    register-with-eureka: true
    fetch-registry: false
    service-url:
      defaultZone: http://192.168.1.1/eureka/

异常 II

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09:42:18.813 [TaskBatchingWorker-target_localhost-9] ERROR c.n.e.c.ReplicationTaskProcessor - Network level connection to peer localhost; retrying after delay
com.sun.jersey.api.client.ClientHandlerException: java.net.ConnectException: Connection refused (Connection refused)
	at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:187)
	at com.netflix.eureka.cluster.DynamicGZIPContentEncodingFilter.handle(DynamicGZIPContentEncodingFilter.java:48)
	at com.netflix.discovery.EurekaIdentityHeaderFilter.handle(EurekaIdentityHeaderFilter.java:27)
	at com.sun.jersey.api.client.Client.handle(Client.java:652)
	at com.sun.jersey.api.client.WebResource.handle(WebResource.java:682)
	at com.sun.jersey.api.client.WebResource.access$200(WebResource.java:74)
	at com.sun.jersey.api.client.WebResource$Builder.post(WebResource.java:570)
	at com.netflix.eureka.transport.JerseyReplicationClient.submitBatchUpdates(JerseyReplicationClient.java:117)
	at com.netflix.eureka.cluster.ReplicationTaskProcessor.process(ReplicationTaskProcessor.java:80)
	at com.netflix.eureka.util.batcher.TaskExecutors$BatchWorkerRunnable.run(TaskExecutors.java:193)
	at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.net.ConnectException: Connection refused (Connection refused)
	at java.base/java.net.PlainSocketImpl.socketConnect(Native Method)
	at java.base/java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:399)
	at java.base/java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:242)
	at java.base/java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:224)
	at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:403)
	at java.base/java.net.Socket.connect(Socket.java:591)
	at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:121)
	at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180)
	at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:144)
	at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:134)
	at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:605)
	at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:440)
	at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835)
	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:118)
	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56)
	at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:173)
	... 10 common frames omitted

erureka server 使用中出现上面的错误，这也是2个注册中心连接复制信息造成的。如果只有一个注册中心，可以用这个禁止：

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eureka:
  server:
    maxThreadsForPeerReplication: 0

原因

在微服务体系中，注册中心是十分重要的一环，注册中心如果死掉，那么所有微服务之间的通讯就没法进行了，整个系统陷入瘫痪。所以eureka才默认就开启了双机模式，这也是开发环境中出现上述2个异常的原因，没有使用双注册中心的备份机制。

生产环境应该使用双注册中心（或更多），不要开启上述几个设置仅仅屏蔽异常。

Spring Security 5.x 开始把密码机制升级了，使用DelegatingPasswordEncoder。 这是一种支持多种加密密码并存的方法，取代了以前只支持一种密码机制的方法。

这种升级需要密码的密文增加一个前缀，来说明密文是通过那种办法加密的，例如之前用 BCryptPasswordEncoder 加密出来的密文

$2a$10$H2z/oHZgviqC8srzsCZq/ObzTNRTfygC4N0NEZlm5trYPFrvdNHeS

需要被存储为：

{bcrypt}$2a$10$H2z/oHZgviqC8srzsCZq/ObzTNRTfygC4N0NEZlm5trYPFrvdNHeS

如果是从 spring security 4.x 升级过了，需要修改下数据库里保存的密文密码。

在开发测试过程中可以使用 {noop}12345 这样的明文密码就比较方便了。

可能遇到的异常或警告

下面2种异常/警告 都是和密码加密有关的。

WARN o.s.s.c.bcrypt.BCryptPasswordEncoder - Encoded password does not look like BCrypt

这个警告是因为密文前缺少{bcypt}，用了BCryptPasswordEncoder去match，Spring 会给出这个警告。

java.lang.IllegalArgumentException: There is no PasswordEncoder mapped for the id “null”

这也是因为密文没有指明加密方式的前缀，用了DelegatingPasswordEncoder去match这个password是否正确，密文的加密方法前缀是null，才出这个错。

其它

另外需要注意的，除了WebSecurityConfigurerAdapter会涉及到登录用户的密码外，在oauth Authentication Server的 ClientDetail 里的 client_secret 也需要类似处理。

参考

https://spring.io/blog/2017/11/01/spring-security-5-0-0-rc1-released#password-encoding

在使用jason做json和类的转换时，遇到错误

Cause: java.lang.RuntimeException: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.LinkedHashMap<java.lang.Object,java.lang.Object>` out of START_ARRAY token

是因为json是数组格式，而提供的待转化成的类是 Map 格式，导致转化失败。

问题表现

在老程序升级到java9或以后版本时，如果遇到 java.lang.NoClassDefFoundError: javax/xml/bind/JAXBException 错误：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'springSecurityFilterChain' defined in class path resource [org/springframework/security/config/annotation/web/configuration/WebSecurityConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.servlet.Filter]: Factory method 'springSecurityFilterChain' threw exception; nested exception is java.lang.NoClassDefFoundError: javax/xml/bind/JAXBException
    at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:645) ~[spring-beans-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:475) ~[spring-beans-5.2.1.RELEASE.jar:5.2.1.RELEASE]

原因

这是由于JAXB API没找到造成的。 JAXB 在是 Java EE API的一部分，在java9开始不再包含在默认的java9的module中（java9开始分module了），甚至在java11开始，干脆把它给移除出JDK了。

解决方法

知道了原因解决办法也就有了：

• 继续用Java8
• 命令后增加 add-modules java.xml.bin，这个方法只对 java9 java10有效
• 一劳永逸的解决问题（对9和以后版本都生效）增加maven依赖（或者gradle）

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<dependency>
  <groupId>jakarta.xml.bind</groupId>
  <artifactId>jakarta.xml.bind-api</artifactId>
  <version>2.3.2</version>
</dependency>

<dependency>
  <groupId>org.glassfish.jaxb</groupId>
  <artifactId>jaxb-runtime</artifactId>
  <version>2.3.2</version>
</dependency>

其它

在 这篇文章：org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat也遇到过相同的JAXBException，解决方式类似。

用java的 Graphics 的 drawString 往图片上描画文字的时候，文字边缘可能会出现粗糙的锯齿（如下图，上部的”文“字的放大效果），可以通过Graphics2D设置抗锯齿效果。

代码和两种的比较效果如下(只有第18行是设置抗锯齿效果的代码)：

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BufferedImage img = new BufferedImage(800, 300, BufferedImage.TYPE_INT_ARGB);
Graphics g = img.getGraphics();

InputStream fi = Thread.currentThread().getContextClassLoader().getResourceAsStream("fonts/msyh.ttf");
BufferedInputStream bisYh = new BufferedInputStream(fi);
Font yahei = Font.createFont(Font.TRUETYPE_FONT, bisYh);

g.setColor(Color.WHITE);
g.fillRect(0, 0, 800, 300);

Font font = yahei.deriveFont(Font.BOLD, 48);
g.setColor(Color.BLACK);

g.setFont(font);
g.drawString("中文字体，无抗锯齿效果", 10, 50);

// 下面这行是设置文字抗锯齿效果的
((Graphics2D) g).setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
g.drawString("中文字体，有抗锯齿效果", 10, 150);

FileOutputStream fos = new FileOutputStream("target/font.png" );
ImageIO.write(img, "png", fos);

fos.flush();
fos.close();

通过上图可以看出，设置抗锯齿效果后，会在文字边缘有些过度颜色的点。如果是要在单色打印机上打印（例如android下连接小票打印机），就不需要这种抗锯齿效果了，有它反而会增加麻烦，我就是在调试android下单色打印机时发现的这个效果。

描画图片时也可以设置抗锯齿效果

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g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

JDK中Graphics2D类 drawString(String str, float x, float y) 方法的后两个参数是用来控制字符串的位置。

这2个参数即不是字符串左上角距画布原点的坐标，也不是左下角距原点的坐标，而是baseline起点距原点的坐标。说到baseline，请参照下图

如上图，红色线是字体描画时的baseline（基线），小写英文字母是可能有些部分在baseline以下的，比如 gjpqy 等，中文每个字都有可能有部分在baseline以下。baseline和字的最上方之间的距离称作 ascent，baseline和最下方之间的距离叫 descent. 这两段距离可以通过 FontMetrics 类获取。

如果要想被画的文字左上角在x,y 位置，可以通过如下代码

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public void drawString(Graphics2D g, String s, float x, float y){
  FontMetrics metrics = g.getFontMetrics(g.getFont());
  g.drawString(s, x, y - metrics.getAscent());
}

通过FontMetrics类，我们还可以获取一段文字的实际占用宽度等，可以实现右对齐和居中对齐

spring boot 项目访问某个controller时出错，错误信息如下：

2019-10-19 09:46:01.451 ERROR 1040 --- [nio-4675-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Circular view path []: would dispatch back to the current handler URL [/] again. Check your ViewResolver setup! (Hint: This may be the result of an unspecified view, due to default view name generation.)] with root cause

javax.servlet.ServletException: Circular view path []: would dispatch back to the current handler URL [/] again. Check your ViewResolver setup! (Hint: This may be the result of an unspecified view, due to default view name generation.)
    at org.springframework.web.servlet.view.InternalResourceView.prepareForRendering(InternalResourceView.java:209) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:147) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:316) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1370) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1116) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1055) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:320) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:119) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:74) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178) ~[spring-security-web-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:357) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:270) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1417) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_131]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_131]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]

这个错误是由于访问的是 Controller， 而该 Controller对方的方法没有对应的视图造成的。 我这里出现这个错误，是因为我本来就不需要视图，我是想返回 JSON，但把 RestController 误写成了 Controller。

字体的大小，在网页中常见单位是px，印刷和word中，常用五号、四号等形式。

印刷常用字号和毫米对应关系

1英寸=72磅=2.54厘米；显示器的

px和pt（磅）之间的换算和DPI有关，DPI有些地方也称作PPI

1pt = DPI / 72 px

• Windows 的默认DPI是 96 （用户可以修改）；
• Mac 的DPI是72

DPI=72时 1英寸显示72px， 1pt = 1px
DPI=96时 1英寸显示96个px, 1pt = 96 / 72 = 1.333px (9pt = 12px)

根据字号对应的磅值，可以得到下表的换算后数值

网页中常用的单位

网页中除了px外，还会用到pt、rem, em,

• em 是指一个字母的宽度（最初指定的是字母M），因为网页默认字体是16px，所以 1em=16px；后来就固定下来了。这个单位会随着浏览器/操作系统放大字号而放大。（px指定的字体在早期IE下不会随着缩放字体而缩放），现在浏览器的缩放功能，都是对整个网页的放大缩小，已经不存在这个问题了。
• % 字体也可以用百分比指定大小，100% = 16px
• pt （win 1pt ≈ 1.333px; max 1pt = 1px)
• cm / mm / in in是inch英寸的缩写， cm是厘米mm是毫米和生活中用到厘米毫米没区别，1in = 2.54cm，这三个单位到px又和DPI相关了。 1in = DPI * 1px；
• ex 和em类似，用的是字母X的高度，很少有人用

CSS3中新增了几个长度单位

• ch字符0的宽度
• rem HTML标签元素的em数
• vm (viewpoint width), 1vm = viewpointwidth * 1%
• vh (viewpoint height), 1vh = viewpointheight * 1%
• vmin = min(viewpoint width, viewpoint height)
• calc(100% - 5px) 表达式，可以做点简单运算

viewpoint在做手机端网页时会用到

在使用微信开发者工具开发小程序时遇到两个怪异问题，记录于此。

websocket 不往服务器端发送 header 信息

某天，突然开始看到报错，小程序的websocket连接不上了，服务端的验证一直通过不，想着没改小程序端，于是一直各种跟踪调试服务端的websocket配置，发现没有收到用于传递身份信息的头导致的。思前想后百思不解，为啥这个头消失了。后来想到电脑有几天没重启过了，之间也没退出过微信开发者工具，尝试退出微信开发者工具，重新进入，问题得以解决。

模拟器中小程序保存图片到相册后自动返回首页

在模拟器中有一个保存图片的功能（把canvas上的图存入相册），保存后，模拟器会弹出一个对话框，选择文件的存储位置，然后保存。有几次没注意文件的位置就存了，存了后，发现小程序自动跳转到了首页，而且console的日志也消失了，好像重启了小程序。原因是弹出的对话框默认是小程序的路径，文件存在了小程序项目目录下，开发者工具检测到了文件变化会重启模拟器内小程序已变反应变化。 换个路径保存就好了。这也不能算开发者工具的bug，只是没注意到这点时，会很麻烦。