2019独角兽企业重金招聘Python工程师标准>>> 
1.在pom文件添加自动配置依赖：
org.springframework.boot spring-boot-autoconfigure
2.如果是某一个jar存在，才能进行配置，则需要添加上该依赖。此处添加 httpclient：
org.apache.httpcomponents httpclient
3.编写默认配置类：
package com.springboot.autoconfig;
import org.springframework.boot.context.properties.ConfigurationProperties;
//在application.properties中进行配置，将覆盖下方的默认值
@ConfigurationProperties(prefix = "spring.httpclient")
public class HttpClientProperties {
private Integer connectTimeOut = 1000;
private Integer socketTimeOut = 10000;
private String agent = "agent";
private Integer maxConnPerRoute = 10;
private Integer maxConnTotaol = 50;
public Integer getConnectTimeOut() {
return connectTimeOut;
}
public void setConnectTimeOut(Integer connectTimeOut) {
this.connectTimeOut = connectTimeOut;
}
public Integer getSocketTimeOut() {
return socketTimeOut;
}
public void setSocketTimeOut(Integer socketTimeOut) {
this.socketTimeOut = socketTimeOut;
}
public String getAgent() {
return agent;
}
public void setAgent(String agent) {
this.agent = agent;
}
public Integer getMaxConnPerRoute() {
return maxConnPerRoute;
}
public void setMaxConnPerRoute(Integer maxConnPerRoute) {
this.maxConnPerRoute = maxConnPerRoute;
}
public Integer getMaxConnTotaol() {
return maxConnTotaol;
}
public void setMaxConnTotaol(Integer maxConnTotaol) {
this.maxConnTotaol = maxConnTotaol;
}
}
4.编写配置自动配置类。该类将读取之前编写的默认配置类在没有配置的情况下，创建默认配置的实例：
package com.springboot.autoconfig;
import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import java.io.IOException;
@Configuration//注明该类是一个Java配置类
@ConditionalOnClass({HttpClient.class})//当HttpClient存在时，才进行自动配置
@EnableConfigurationProperties(HttpClientProperties.class)//读取默认配置
public class HttpClientAutoConfiguration {
private final HttpClientProperties properties;
//在application.properties中进行配置，将使用其创建好的配置
public HttpClientAutoConfiguration(HttpClientProperties properties){
this.properties = properties;
}
@Bean//声明为bean,才能自动注入
@ConditionalOnMissingBean(HttpClient.class)//当不存在创建好的HttpClient实例，将使用该方法进行创建
public HttpClient httpClient(){
//构建requestConfig
RequestConfig requestConfig = RequestConfig.custom()
.setConnectTimeout(properties.getConnectTimeOut())//设置连接超时时间，默认1秒
.setSocketTimeout(properties.getSocketTimeOut()).build();//设置读超时时间，默认10秒
HttpClient client = HttpClientBuilder.create()
.setDefaultRequestConfig(requestConfig) //设置requestConfig
.setUserAgent(properties.getAgent())//设置User-Agent
.setMaxConnPerRoute(properties.getMaxConnPerRoute())//设置一个远端IP最大的连接数
.setMaxConnTotal(properties.getMaxConnTotaol())//设置总的连接数
.build();
return client;
}
@Bean
@ConditionalOnBean(name="httpClient",value=HttpClient.class)//已存在HttpClient实例httpClient
@ConditionalOnProperty(name = "spring.httpclient.testConfig", havingValue = "true")//读取配置是否设置该属性为true
public HttpClient httpClient1(HttpClient httpClient) throws IOException {
Long contentLength=httpClient.execute(new HttpGet("https://www.taobao.com")).getEntity().getContentLength();
if(contentLength>10){
System.out.println("test success..");
}else{
System.out.println("test fail..");
}
return httpClient;
}
}@ConditionalOnMissingBean：若用户没有自定义某个bean，才会构建这个bean
@ConditionalOnProperty：若用户没有开启某一个属性，则不会构建。只有开启才会构建
@ConditionalOnClass：某个类存在的情况下，才会去构建。
5.编写测试类：
package com.springboot;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.util.EntityUtils;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import java.io.IOException;
@RunWith(SpringRunner.class)
@SpringBootTest
public class SelfStarterApplicationTests {
/**
* 检测我们编写的自动配置HttpClientAutoConfiguration有没有生效
*/
@Autowired
private HttpClient httpClient;
@Autowired
private HttpClient httpClient1;
/**
* httpclient bean 的定义
* 有三种方式都可以让HttpClientAutoConfiguration这个自动配置生效
* 1.通过将自动配置所在package成为注解了@SpringBootApplication启动类的子package
* 2.通过定义META-INF/spring.factories文件，里面添加EnableAutoConfiguration与自动配置的映射关系
* 3.通过在启动类中添加注解EnableHttpClient,EnableHttpClient要@Import(HttpClientAutoConfiguration.class)
* @return
*/
@Test
public void testHttclient() throws IOException {
//访问百度，输出百度网页
System.out.println(EntityUtils.toString(httpClient.execute(new HttpGet("http://www.baidu.com")).getEntity()));
}
@Test
public void testHttclient1() throws IOException {
//访问百度，输出百度网页
System.out.println(EntityUtils.toString(httpClient1.execute(new HttpGet("http://www.baidu.com")).getEntity()));
}
}
6.此时，由于当前package在应用程序入口类之下，所以将直接自动扫描注解@Configuration：
运行测试类方法，可以成功返回结果。
若当前package不在应用程序入口类之下，也就是正常情况下，发布到外部作为第三方依赖时。此时将无法自动扫描到注解，解决方案有两个：
方案一.创建自定义注解：
package com.springboot.autoconfig;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(HttpClientAutoConfiguration.class)
public @interface EnableHttpClient {
}
在注解中，使用@Import(HttpClientAutoConfiguration.class) 引入了HttpClientAutoConfiguration 配置。此时，只需要将应用程序入口添加上自定义注解即可：
package com.springboot;
import com.springboot.autoconfig.EnableHttpClient;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@EnableHttpClient
@SpringBootApplication
public class SelfStarterApplication {
public static void main(String[] args) {
SpringApplication.run(SelfStarterApplication.class, args);
}
}方案二.创建spring.factories，定义扫描类：
spring.factories：
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.springboot.autoconfig.HttpClientAutoConfiguration文件放在resources目录下的META-INF下：
两者的使用辨析：
- 使用方案二时，在添加了依赖之后，就一定会去自动扫描配置；
- 使用方案一时，在添加了依赖之后，还需要在应用入口添加自定义注解才能开启自动扫描配置。
这两种方案在实际使用过程是都有使用的。
7.后续操作：使用mvn命令将项目打成Jar包，添加了本地仓库，即可在其他项目引入其依赖并完成相关的自动配置：
com.springboot org.springframework.boot spring-boot-starter org.springframework.boot spring-boot-starter-test test org.springframework.boot spring-boot-starter-web self-starter 0.0.1-SNAPSHOT
相关程序：https://gitee.com/LangWangHuangShiFu/self-starter