如何理解DubboDefaultProperties EnvironmentPostProcessor

如何理解DubboDefaultProperties EnvironmentPostProcessor，相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。

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本文主要研究一下DubboDefaultPropertiesEnvironmentPostProcessor

DubboDefaultPropertiesEnvironmentPostProcessor

dubbo-spring-boot-project-2.7.3/dubbo-spring-boot-compatible/autoconfigure/src/main/java/org/apache/dubbo/spring/boot/env/DubboDefaultPropertiesEnvironmentPostProcessor.java

public class DubboDefaultPropertiesEnvironmentPostProcessor implements EnvironmentPostProcessor, Ordered {    /**     * The name of default {@link PropertySource} defined in SpringApplication#configurePropertySources method.     */    public static final String PROPERTY_SOURCE_NAME = "defaultProperties";    /**     * The property name of "spring.main.allow-bean-definition-overriding".     * Please refer to: https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.1-Release-Notes#bean-overriding     */    public static final String ALLOW_BEAN_DEFINITION_OVERRIDING_PROPERTY = "spring.main.allow-bean-definition-overriding";    @Override    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {        MutablePropertySources propertySources = environment.getPropertySources();        Map defaultProperties = createDefaultProperties(environment);        if (!CollectionUtils.isEmpty(defaultProperties)) {            addOrReplace(propertySources, defaultProperties);        }    }    @Override    public int getOrder() {        return LOWEST_PRECEDENCE;    }    private Map createDefaultProperties(ConfigurableEnvironment environment) {        Map defaultProperties = new HashMap();        setDubboApplicationNameProperty(environment, defaultProperties);        setDubboConfigMultipleProperty(defaultProperties);        setDubboApplicationQosEnableProperty(defaultProperties);        setAllowBeanDefinitionOverriding(defaultProperties);        return defaultProperties;    }    private void setDubboApplicationNameProperty(Environment environment, Map defaultProperties) {        String springApplicationName = environment.getProperty(SPRING_APPLICATION_NAME_PROPERTY);        if (StringUtils.hasLength(springApplicationName)                && !environment.containsProperty(DUBBO_APPLICATION_NAME_PROPERTY)) {            defaultProperties.put(DUBBO_APPLICATION_NAME_PROPERTY, springApplicationName);        }    }    private void setDubboConfigMultipleProperty(Map defaultProperties) {        defaultProperties.put(DUBBO_CONFIG_MULTIPLE_PROPERTY, Boolean.TRUE.toString());    }    private void setDubboApplicationQosEnableProperty(Map defaultProperties) {        defaultProperties.put(DUBBO_APPLICATION_QOS_ENABLE_PROPERTY, Boolean.FALSE.toString());    }    /**     * Set {@link #ALLOW_BEAN_DEFINITION_OVERRIDING_PROPERTY "spring.main.allow-bean-definition-overriding"} to be     * true as default.     *     * @param defaultProperties the default {@link Properties properties}     * @see #ALLOW_BEAN_DEFINITION_OVERRIDING_PROPERTY     * @since 2.7.1     */    private void setAllowBeanDefinitionOverriding(Map defaultProperties) {        defaultProperties.put(ALLOW_BEAN_DEFINITION_OVERRIDING_PROPERTY, Boolean.TRUE.toString());    }    /**     * Copy from BusEnvironmentPostProcessor#addOrReplace(MutablePropertySources, Map)     *     * @param propertySources {@link MutablePropertySources}     * @param map             Default Dubbo Properties     */    private void addOrReplace(MutablePropertySources propertySources,                              Map map) {        MapPropertySource target = null;        if (propertySources.contains(PROPERTY_SOURCE_NAME)) {            PropertySource source = propertySources.get(PROPERTY_SOURCE_NAME);            if (source instanceof MapPropertySource) {                target = (MapPropertySource) source;                for (String key : map.keySet()) {                    if (!target.containsProperty(key)) {                        target.getSource().put(key, map.get(key));                    }                }            }        }        if (target == null) {            target = new MapPropertySource(PROPERTY_SOURCE_NAME, map);        }        if (!propertySources.contains(PROPERTY_SOURCE_NAME)) {            propertySources.addLast(target);        }    }}

• DubboDefaultPropertiesEnvironmentPostProcessor实现了EnvironmentPostProcessor, Ordered接口；postProcessEnvironment方法首先从environment获取MutablePropertySources，然后通过createDefaultProperties创建默认配置defaultProperties(这里默认设置了DUBBO_APPLICATION_NAME_PROPERTY为springApplicationName、DUBBO_CONFIG_MULTIPLE_PROPERTY为true、DUBBO_APPLICATION_QOS_ENABLE_PROPERTY为false)，最后通过addOrReplace方法把defaultProperties覆盖到propertySources；getOrder方法返回的是LOWEST_PRECEDENCE

DubboDefaultPropertiesEnvironmentPostProcessorTest

dubbo-spring-boot-project-2.7.3/dubbo-spring-boot-autoconfigure/src/test/java/org/apache/dubbo/spring/boot/env/DubboDefaultPropertiesEnvironmentPostProcessorTest.java

public class DubboDefaultPropertiesEnvironmentPostProcessorTest {    private DubboDefaultPropertiesEnvironmentPostProcessor instance =            new DubboDefaultPropertiesEnvironmentPostProcessor();    private SpringApplication springApplication = new SpringApplication();    @Test    public void testOrder() {        Assert.assertEquals(Ordered.LOWEST_PRECEDENCE, instance.getOrder());    }    @Test    public void testPostProcessEnvironment() {        MockEnvironment environment = new MockEnvironment();        // Case 1 : Not Any property        instance.postProcessEnvironment(environment, springApplication);        // Get PropertySources        MutablePropertySources propertySources = environment.getPropertySources();        // Nothing to change        PropertySource defaultPropertySource = propertySources.get("defaultProperties");        Assert.assertNotNull(defaultPropertySource);        Assert.assertEquals("true", defaultPropertySource.getProperty("dubbo.config.multiple"));        Assert.assertEquals("false", defaultPropertySource.getProperty("dubbo.application.qos-enable"));        // Case 2 :  Only set property "spring.application.name"        environment.setProperty("spring.application.name", "demo-dubbo-application");        instance.postProcessEnvironment(environment, springApplication);        defaultPropertySource = propertySources.get("defaultProperties");        Object dubboApplicationName = defaultPropertySource.getProperty("dubbo.application.name");        Assert.assertEquals("demo-dubbo-application", dubboApplicationName);        // Case 3 : Only set property "dubbo.application.name"        // Rest environment        environment = new MockEnvironment();        propertySources = environment.getPropertySources();        environment.setProperty("dubbo.application.name", "demo-dubbo-application");        instance.postProcessEnvironment(environment, springApplication);        defaultPropertySource = propertySources.get("defaultProperties");        Assert.assertNotNull(defaultPropertySource);        dubboApplicationName = environment.getProperty("dubbo.application.name");        Assert.assertEquals("demo-dubbo-application", dubboApplicationName);        // Case 4 : If "defaultProperties" PropertySource is present in PropertySources        // Rest environment        environment = new MockEnvironment();        propertySources = environment.getPropertySources();        propertySources.addLast(new MapPropertySource("defaultProperties", new HashMap()));        environment.setProperty("spring.application.name", "demo-dubbo-application");        instance.postProcessEnvironment(environment, springApplication);        defaultPropertySource = propertySources.get("defaultProperties");        dubboApplicationName = defaultPropertySource.getProperty("dubbo.application.name");        Assert.assertEquals("demo-dubbo-application", dubboApplicationName);        // Case 5 : Rest dubbo.config.multiple and dubbo.application.qos-enable        environment = new MockEnvironment();        propertySources = environment.getPropertySources();        propertySources.addLast(new MapPropertySource("defaultProperties", new HashMap()));        environment.setProperty("dubbo.config.multiple", "false");        environment.setProperty("dubbo.application.qos-enable", "true");        instance.postProcessEnvironment(environment, springApplication);        Assert.assertEquals("false", environment.getProperty("dubbo.config.multiple"));        Assert.assertEquals("true", environment.getProperty("dubbo.application.qos-enable"));    }}

• testPostProcessEnvironment方法通过MockEnvironment验证了DubboDefaultPropertiesEnvironmentPostProcessor的addOrReplace方法

小结

DubboDefaultPropertiesEnvironmentPostProcessor实现了EnvironmentPostProcessor, Ordered接口；postProcessEnvironment方法首先从environment获取MutablePropertySources，然后通过createDefaultProperties创建默认配置defaultProperties(这里默认设置了DUBBO_APPLICATION_NAME_PROPERTY为springApplicationName、DUBBO_CONFIG_MULTIPLE_PROPERTY为true、DUBBO_APPLICATION_QOS_ENABLE_PROPERTY为false)，最后通过addOrReplace方法把defaultProperties覆盖到propertySources；getOrder方法返回的是LOWEST_PRECEDENCE

doc

• DubboDefaultPropertiesEnvironmentPostProcessor

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