1.前言

我們用spring boot發(fā)現(xiàn)會有很多spring-boot-starter-xxx，在實際開發(fā)中可能會通過@Bean注解來實現(xiàn)組件的加載，我們希望通過配置文件如application.yml或者application.properties來實現(xiàn)自定義類的加載到spring 容器中去。
本文采用spring boot版本為2.1.1為例。
官方文檔建議我們自定義組件命名最好采用xxx-spring-boot-starter 命名規(guī)則參考。

2.準備知識

3.依賴

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-autoconfigure</artifactId>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-configuration-processor</artifactId>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <scope>provided</scope>
    </dependency>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
      <scope>provided</scope>
    </dependency>

    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>${fast.json}</version>
    </dependency>

4.代碼實現(xiàn)

1.創(chuàng)建FastJsonProperties類,主要是放默認的fastJson配置文件。

@ConditionalOnClass({JSON.class})
@ConfigurationProperties(prefix = "spring.fastjson")
public class FastJsonProperties {
    /**
     * 默認Content-Type
     */
    private final static String DEFAULT_MEDIA_TYPE = "application/json;charset=UTF-8";
    /**
     * 是否生效
     */
    private boolean enabled;
    /**
     * 默認List<MediaType>
     */
    private List<MediaType> supportedMediaTypes = MediaType.parseMediaTypes(DEFAULT_MEDIA_TYPE);
    /**
     * 實例化一個FastJsonConfig對象
     */
    private FastJsonConfig config = new FastJsonConfig();

    public boolean isEnabled() {
        return enabled;
    }

    public void setEnabled(boolean enabled) {
        this.enabled = enabled;
    }

    public List<MediaType> getSupportedMediaTypes() {
        return supportedMediaTypes;
    }

    public void setSupportedMediaTypes(List<MediaType> supportedMediaTypes) {
        this.supportedMediaTypes = supportedMediaTypes;
    }

    public FastJsonConfig getConfig() {
        return config;
    }

    public void setConfig(FastJsonConfig config) {
        this.config = config;
    }

2.創(chuàng)建FastJsonAutoConfiguration類。

• (1)注入配置文件類。
• (2)過濾配置文件值判斷是否生效。
• (3)重新構(gòu)造HttpMessageConverter方法。
• (4)把bean注入到容器中。

@Configuration
@EnableConfigurationProperties({FastJsonProperties.class})
@ConditionalOnClass({JSON.class, HttpMessageConverter.class})
public class FastJsonAutoConfiguration {
    @Resource
    private FastJsonProperties fastJsonProperties;
    @Bean
    @ConditionalOnProperty(prefix = "spring.fastjson", name = "enabled", havingValue = "true", matchIfMissing = true)
    @ConditionalOnWebApplication
    public HttpMessageConverter<?> httpMessageConverter() {
        /**
         * FastJsonHttpMessageConverter轉(zhuǎn)換類
         */
        FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
        /*媒體類型*/
        fastJsonHttpMessageConverter.setSupportedMediaTypes(fastJsonProperties.getSupportedMediaTypes());
        /*配置*/
        fastJsonHttpMessageConverter.setFastJsonConfig(fastJsonProperties.getConfig());
        return fastJsonHttpMessageConverter;
    }

3.在resources下的META-INF里創(chuàng)建spring.factories文件,spring boot通個這個文件來掃包把我們的bean加載到容器中

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.even.fastjson.FastJsonAutoConfiguration

4.為了讓IDE編輯器能提示我們一些配置提示我們自己創(chuàng)建一個spring-configuration-metadata.json文件里面添加一些元數(shù)據(jù)。
參考文檔

{
  "properties": [
    {
      "name": "spring.fastjson.supportedMediaTypes",
      "type": "java.lang.String",
      "description": "Description for spring.fastjson.supportedMediaTypes.",
      "defaultValue": "application/json;charset=UTF-8"
    },
    {
      "name": "spring.fastjson.config.serializerFeatures",
      "type": "com.alibaba.fastjson.serializer.SerializerFeature",
      "description": "Description for spring.fastjson.config.serializerFeatures."
    },
    {
      "name": "spring.fastjson.enabled",
      "type": "java.lang.Boolean",
      "description": "Whether to enable FastJsonHttpMessageConverter.",
      "defaultValue": true
    },
    {
      "name": "spring.fastjson.config.dateFormat",
      "type": "java.lang.String",
      "description": "Date serialization format."
    }
  ],
  "hints": [
    {
      "name": "spring.fastjson.supportedMediaTypes",
      "values": [
        {
          "value": "application/json;charset=UTF-8"
        },
        {
          "value": "text/html"
        },
        {
          "value": "text/plain"
        },
        {
          "value": "text/xml"
        }
      ]
    },
    {
      "name": "spring.fastjson.config.serializerFeatures",
      "providers": [
        {
          "name": "handle-as",
          "parameters": {
            "target": "com.alibaba.fastjson.serializer.SerializerFeature"
          }
        }
      ]
    },
    {
      "name": "spring.fastjson.enabled",
      "values": [
        {
          "value": true
        },
        {
          "value": false
        }
      ]
    },
    {
      "name": "spring.fastjson.config.dateFormat",
      "values": [
        {
          "value": "yyyy-MM-dd"
        },
        {
          "value": "yyyy-MM-dd HH:mm:ss"
        },
        {
          "value": "HH:mm:ss"
        }
      ]
    }
  ]
}

6.自定義starter代碼完成了需要打成jar包,別的spring-boot只需要將這個包引用進來。
注意打包的時候看一下target/classes/META-INF/下是否有spring.factories文件,我打包的時候出現(xiàn)了沒有這個文件導致我測試fastjson一直不生效。
7.測試

• (1)創(chuàng)建一個新的spring-boot項目。
• (2)引入spring-boot-fastjson-starter包。
• (3)在配置文件開啟spring.fastjson.enabled=true。
• (4)寫一個demo這里就省略demo。
  User類

@AllArgsConstructor
@NoArgsConstructor
@Setter
@Getter
@Builder
public class User {
    //去掉ID
    @JSONField(serialize=false)
    private Long id;
    @JSONField(ordinal = 3)
    private String name;
    private int age;
    @JSONField(ordinal = 1)
    private LocalDate birthday;
}

(5)輸出結(jié)果:{"age":20,"birthday":"2018-12-21","name":"even"}

5.資料

• 參考文檔:spring-boot文檔
• 參考源碼:fastjson-spring-boot-starter
• 筆者源碼地址:spring-boot-fastjson-starter
• 筆者測試demo源碼地址:spring-boot-fastjson
• 筆者郵箱:even366@qq.com