From https://www.cnblogs.com/duanxz/p/9337022.html

Spring Boot 內嵌容器Undertow參數設置

配置項：

# 設置IO線程數, 它主要執行非阻塞的任務,它們會負責多個連接, 默認設置每個CPU核心一個線程
# 不要設置過大，如果過大，啓動項目會報錯：打開文件數過多
server.undertow.io-threads=16

# 阻塞任務線程池, 當執行類似servlet請求阻塞IO操作, undertow會從這個線程池中取得線程
# 它的值設置取決於系統線程執行任務的阻塞係數，默認值是IO線程數*8
server.undertow.worker-threads=256

# 以下的配置會影響buffer,這些buffer會用於服務器連接的IO操作,有點類似netty的池化內存管理
# 每塊buffer的空間大小,越小的空間被利用越充分，不要設置太大，以免影響其他應用，合適即可
server.undertow.buffer-size=1024

# 每個區分配的buffer數量 , 所以pool的大小是buffer-size * buffers-per-region
server.undertow.buffers-per-region=1024

# 是否分配的直接內存(NIO直接分配的堆外內存)
server.undertow.direct-buffers=true

來看看源代碼：

https://github.com/undertow-io/undertow/blob/master/core/src/main/java/io/undertow/Undertow.java

ioThreads = Math.max(Runtime.getRuntime().availableProcessors(), 2);

workerThreads = ioThreads * 8;

//smaller than 64mb of ram we use 512b buffers
if (maxMemory < 64 * 1024 * 1024) {
    //use 512b buffers
    directBuffers = false;
    bufferSize = 512;
} else if (maxMemory < 128 * 1024 * 1024) {
    //use 1k buffers
    directBuffers = true;
    bufferSize = 1024;
} else {
    //use 16k buffers for best performance
    //as 16k is generally the max amount of data that can be sent in a single write() call
    directBuffers = true;
    bufferSize = 1024 * 16 - 20; //the 20 is to allow some space for protocol headers, see UNDERTOW-1209
}

很顯然，Undertow認爲它的運用場景是在IO密集型的系統應用中，並且認爲多核機器是一個比較容易滿足的點，Undertow初始化假想應用的阻塞係數在0.8~0.9之間，所以阻塞線程數直接乘了個8，當然，如果對應用較精確的估測阻塞係數，可以配置上去。

Spring Boot內嵌容器支持Tomcat、Jetty、Undertow。爲什麼選擇Undertow？

這裏有一篇文章，時間 2017年1月26日發佈的：
Tomcat vs. Jetty vs. Undertow: Comparison of Spring Boot Embedded Servlet Containers

1. Setup Spring Boot Application

We will use Maven to setup a new project in Eclipse with the appropriate dependencies. We will use the starter parent for this example but the dependencies in a production application will likely be altered to streamline, optimize or customize.

1.1 Setup Spring Boot Dependencies

The default embedded servlet container is Tomcat. This version of Spring Web 1.4.3 brings in Tomcat version 8.5.6.

pom.xml

<parent>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-parent</artifactId>
   <version>1.4.3.RELEASE</version>
</parent>
 
<dependencies>
   <!-- TOMCAT -->
   <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
   </dependency>
</dependencies>

1.2 Setup Spring Boot Main Application and Controllers

To setup the Spring Boot application you include the @SpringBootApplication annotation in your Main class. The @SpringBootApplication annotation brings in @SpringBootConfiguration, @EnableAutoConfiguration and @ComponentScanannotations.

Application.java

@SpringBootApplication
@ConfigurationProperties
public class Application {
public static void main(String[] args) {
   SpringApplication.run(Application.class, args);
}

You may choose to eliminate this annotation and add the @SpringBootConfiguration alone or to another class that allows you to customize the configuration. The @ComponentScan will scan your application for items like the @Controller you will need to setup a RESTful service. The following controller will return a simple “Hello World” string from a HTTP GET request. We have also included in the bundled example another endpoint mapping that returns a complex object type.

SampleController.java

@Controller
public class SampleController {

@Autowired
private ResourceLoader resourceLoader;

@RequestMapping("/")
@ResponseBody
public String home() {
   return "Hello World!";
}

1.3 Key Configuration Parameters

The default properties for all the embedded servlet containers are the same. Some of the most important properties to consider are the properties for configuring startup information like ports and application name, TSL, access logs, compression and many more.

For example, to configure SSL add the following to key value pairs to the application.properties.

application.properties

server.port=8443
server.ssl.key-store=classpath:keystore.jks
server.ssl.key-store-password=secret
server.ssl.key-password=another-secret

1.4 How to Find Additional Parameters

To explore the parameters for Spring boot applications you can add the Spring actuator dependency and the @ConfigurationProperties annotation to your Main class. You then visit the /configprops endpoint on your application to get a list of the available properties.

Application.java

@SpringBootApplication
@ConfigurationProperties
public class Application {

pom.xml

<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

http://localhost:8080/jcg/service/configprops

1.5 Change version of Embedded Servlet Containers

The embedded servlet container versions are defined in the following parent dependency from the pom. You can change the version of the embedded servlet container by explicitly including the dependency and identifying a new version in the pom. We will show you how in the examples below.

pom.xml

<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-dependencies</artifactId>
   <version>1.3.7.RELEASE</version>
</dependency>

2. Tomcat

As Tomcat is the default embedded servlet container there is nothing you need to do to the default implementation to use Tomcat. You can change the version of Tomcat you are using or change properties in the pom.xml or application.properties files.

2.2 Change Version of Tomcat

pom.xml

<properties>
   <tomcat.version>8.5.6</tomcat.version></properties>
<dependency>
   <groupId>org.apache.tomcat.embed</groupId>
   <artifactId>tomcat-embed-core</artifactId>
   <version>${tomcat.version}</version>
</dependency>
<dependency>
   <groupId>org.apache.tomcat.embed</groupId>
   <artifactId>tomcat-embed-el</artifactId>
   <version>${tomcat.version}</version>
</dependency>
<dependency>
   <groupId>org.apache.tomcat.embed</groupId>
   <artifactId>tomcat-embed-websocket</artifactId>
   <version>${tomcat.version}</version>
</dependency>

3. Jetty

To change the embedded servlet container to Jetty you need to edit the pom file to remove the Tomcat dependency and add Jetty.

3.1 Change to Jetty (version 9.3.14)

pom.xml

<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-web</artifactId>
   <exclusions>
      <exclusion>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-tomcat</artifactId>
      </exclusion>
   </exclusions>
</dependency>
<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

4. Undertow

To change the embedded servlet container to Undertow you need to edit the pom file to remove the Tomcat dependency and add Undertow.

4.1 Change to Undertow (version 1.3.24 final)

Notice the undertow version included in the spring boot starter is incorrect, referring to 1.3.25. You’ll need to change it to 1.3.24.Final for this to work at the time of this article.

pom.xml

<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-web</artifactId>
   <exclusions>
      <exclusion>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-tomcat</artifactId>
      </exclusion>
   </exclusions>
</dependency>
<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>
<dependency>
   <groupId>io.undertow</groupId>
   <artifactId>undertow-core</artifactId>
   <version>1.3.24.Final</version>
</dependency>
<dependency>
   <groupId>io.undertow</groupId>
   <artifactId>undertow-servlet</artifactId>
   <version>1.3.24.Final</version>
</dependency>

5. Performance and Load

In this example, we will analyze both the peformance of HTTP requests and the memory footprint at startup of all three embedded servlet containers. We used JMeter to measure performance by simulating load and JVisualVM to look at the memory footprint.

5.1 Measure Performance

In this example, we will analyze both the peformance of simple RESTFul GET requests that return a string and more complex GET requests that return complex JSON objects. JMeter is the tool used to measure the performance of the the three different types of containers. The key to setting up this test was establishing thread groups with the appropriate load, a counter to dynamically update the input to the API and report viewers to display or aggregate the results. For the simple string examples, we used a thread group with 1000 threads that would loop 3 times through the sequence. It also used a ramp up time of 10 seconds. For the complex object examples, we used the same parameters but did not loop.

JMeter Tomcat Thread Group

JMeter Tomcat Summary Report

5.1.1 Tomcat

5.1.1.1 Simple String

Label	# Samples	Average	Min	Max	Std. Dev.	Throughput	Received KB/sec	Sent KB/sec	Avg. Bytes
Startup	3000	7	1	549	35.78374361	293.8583603	55.95935572	55.67238466	195
Others	3000	1	0	45	1.359661682	287.8802418	54.82094449	54.53981144	195
Others	3000	1	0	24	1.155032275	292.1129503	55.62697785	55.3417113	195

5.1.1.2 Complex Object with Dynamic Data

Label	# Samples	Average	Min	Max	Std. Dev.	Throughput	Received KB/sec	Sent KB/sec	Avg. Bytes
Startup	1000	114	3	1601	322.8671905	97.68486861	202.3335999	19.93763432	2121
Others	1000	3	2	17	1.328216473	97.88566954	202.7495167	19.9786181	2121
Others	1000	2	1	16	1.110529603	98.52216749	204.0678879	20.10852833	2121
Others	1000	2	1	21	1.344498419	98.53187506	204.0879951	20.11050966	2121

5.1.2 Jetty

5.1.2.1 Simple Object

Label	# Samples	Average	Max	Std. Dev.	Throughput	Received KB/sec	Sent KB/sec	Avg. Bytes
Startup	3000	7	561	40.13705065	291.5168594	56.0828333	55.22878	197
Others	3000	1	21	1.058925031	293.5995302	56.48350338	55.6233485	197
Others	3000	1	21	0.926034317	294.3485086	56.62759395	55.7652448	197

5.1.2.2 Complex Object with Dynamic Data

Label	# Samples	Average	Min	Max	Std. Dev.	Throughput	Received KB/sec	Sent KB/sec	Avg. Bytes
Startup	1000	110	3	1397	278.7961107	98.13542689	203.3626717	19.93375859	2122
Others	1000	3	2	20	1.500210319	98.48335631	204.0836739	20.00443175	2122
Others	1000	3	2	45	2.729377218	98.29942003	203.7025091	19.96706969	2122

5.1.3 Undertow

5.1.3.1 Simple Object

Label	# Samples	Average	Max	Std. Dev.	Throughput	Received KB/sec	Sent KB/sec	Avg. Bytes
Startup	3000	6	451	31.6188702	295.6830278	63.81440346	56.01807363	221
Others	3000	1	22	1.255447862	292.7400468	63.17924839	55.46051669	221
Others	3000	1	18	1.559477975	294.3773918	63.53262069	55.77071681	221

5.1.3.2 Complex Object with Dynamic Data

Label	# Samples	Average	Min	Max	Std. Dev.	Throughput	Received KB/sec	Sent KB/sec	Avg. Bytes
Startup	1000	70	3	1114	197.1333241	97.059109	203.3969361	19.62044201	2145.893
Startup	1000	42	3	852	132.6443576	98.02960494	205.6324135	20.00799554	2148
Others	1000	3	2	19	1.293570253	98.55129595	206.6305004	20.01823199	2147
Others	1000	2	2	27	1.659250132	98.74592673	207.0385788	20.05776637	2147
Others	1000	2	1	17	1.260904041	98.28975821	206.0821395	19.96510714	2147

5.2 Measure Memory

To measure the memory of each embedded servlet container we looked at the memory usage on startup. JVisualVM is a tool provided with the Java Development Kit for visualizing the memory and footprint of java applications. We used this tool to show the initial startup impact of each of the three embedded servlet containers. The heap size and thread counts are key in analyzing this initial footprint. The ten threads that are common to all three containers include: JMX server connection timeout, RMI Scheduler, RMI TCP Connection (2), RMI TCP Accept, Attach Listener, DestroyJavaVM, Signal Dispatcher, Finalizer and Reference Handler.

JVisualVM Report

5.2.2 Tomcat

Heap Size: 697,827,328 B
Used: 124,260,976 B
Max: 2,147,483,648 B

Threads: 17 Live, 22 Started

5.2.3 Jetty

Heap Size: 628,621,312 B
Used: 311,476,776 B
Max: 2,147,483,648 B

Threads: 19 Live, 22 Started

5.2.4 Undertow

Heap Size: 630,718,464 B
Used: 114,599,536 B
Max: 2,147,483,648 B

Threads: 17 Live, 20 Started

6. 對比

6.1 性能

壓測結果：從上面的6張壓力測試報告中，可以看到3個容器在相同的用例及併發請求下，Undertow稍微比Tomcat和Jetty好一點。

資源消耗：JETY啓動時內存佔用最大，使用311 MB。Tomcat和Undertow的初始腳印相似，在120 MB左右，Undertow出現在114 MB的最低水平。響應頭中的關鍵差異在於默認情況下默認情況下包括HTTP持久連接。該頭將在支持持久連接的客戶端中使用，以通過重用連接細節來優化性能。

6.1.1 Tomcat Response Headers

Content-Type →application/json;charset=UTF-8
Date →Mon, 09 Jan 2017 02:23:26 GMT
Transfer-Encoding →chunked
X-Application-Context →JcgSpringBootContainers:# Application index.

6.1.2 Jetty Response Headers

Content-Type →application/json;charset=UTF-8
Date →Mon, 09 Jan 2017 02:29:21 GMT
Transfer-Encoding →chunked
X-Application-Context →JcgSpringBootContainers:# Application index.

6.1.3 Undertow Response Headers

Connection →keep-alive
Content-Type →application/json;charset=UTF-8
Date →Mon, 09 Jan 2017 02:20:25 GMT
Transfer-Encoding →chunked
X-Application-Context →JcgSpringBootContainers:# Application index.

7. 結論

這些數字表明Undertow在性能和內存使用方面是最好的。令人鼓舞的是，Undertow 正在接受最新的能力，並默認爲持久的連接。這些數字並不表示在這個例子中使用的負載有顯著的性能差異，但我想它們會縮放，如果性能是最重要的因素，則Undertow 是應用程序的正確匹配。認爲一個組織可能因爲熟悉它的能力而喜歡嵌入的servlet容器也是合理的。很多時候默認設置將不得不改變，因爲應用程序要求包括性能、內存使用和功能。

=========================分割線=================================================================================

在Spring Boot中使用 Undertow 而不是 Tomcat

1、Maven示例：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

2、配置Undertow，application.yml示例：

server.undertow.accesslog.dir= # Undertow access log directory.
server.undertow.accesslog.enabled=false # Enable access log.
server.undertow.accesslog.pattern=common # Format pattern for access logs.
server.undertow.accesslog.prefix=access_log. # Log file name prefix.
server.undertow.accesslog.rotate=true # Enable access log rotation.
server.undertow.accesslog.suffix=log # Log file name suffix.
server.undertow.buffer-size= # Size of each buffer in bytes.
server.undertow.buffers-per-region= # Number of buffer per region.
server.undertow.direct-buffers= # Allocate buffers outside the Java heap.
server.undertow.io-threads= # Number of I/O threads to create for the worker.
server.undertow.max-http-post-size=0 # Maximum size in bytes of the HTTP post content.
server.undertow.worker-threads= # Number of worker threads.

3、使用 Undertow 監聽多個端口示例：

@Bean
public UndertowEmbeddedServletContainerFactory embeddedServletContainerFactory() {
    UndertowEmbeddedServletContainerFactory factory = new UndertowEmbeddedServletContainerFactory();
    factory.addBuilderCustomizers(new UndertowBuilderCustomizer() {

        @Override
        public void customize(Builder builder) {
            builder.addHttpListener(8080, "0.0.0.0");
        }

    });
    return factory;
}

Spring Boot 容器選擇 Undertow 而不是 Tomcat

Spring Boot 內嵌容器Undertow參數設置

1. Setup Spring Boot Application

1.1 Setup Spring Boot Dependencies

1.2 Setup Spring Boot Main Application and Controllers

1.3 Key Configuration Parameters

1.4 How to Find Additional Parameters

1.5 Change version of Embedded Servlet Containers

2. Tomcat

2.2 Change Version of Tomcat

3. Jetty

3.1 Change to Jetty (version 9.3.14)

4. Undertow

4.1 Change to Undertow (version 1.3.24 final)

5. Performance and Load

5.1 Measure Performance

5.2 Measure Memory

6. 對比

6.1 性能

7. 結論

在Spring Boot中使用 Undertow 而不是 Tomcat

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