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本文主要研究一下spring boot tomcat jdbc pool的属性绑定

错误配置

spring:
  datasource:
    type: org.apache.tomcat.jdbc.pool.DataSource
    driver-class-name: org.postgresql.Driver
    url: jdbc:postgresql://192.168.99.100:5432/postgres?connectTimeout=6000&socketTimeout=6000
    username: postgres
    password: postgres
    jmx-enabled: true
    initial-size: 1
    max-active: 5
    ## when pool sweeper is enabled, extra idle connection will be closed
    max-idle: 5
    ## when idle connection > min-idle, poolSweeper will start to close
    min-idle: 1

使用如上配置，最后发现initial-size，max-active，max-idle，min-idle等配置均无效，生成的tomcat jdbc datasource还是使用的默认的配置

正确配置

spring:
  datasource:
    type: org.apache.tomcat.jdbc.pool.DataSource
    driver-class-name: org.postgresql.Driver
    url: jdbc:postgresql://192.168.99.100:5432/postgres?connectTimeout=6000&socketTimeout=6000
    username: postgres
    password: postgres
    jmx-enabled: true
    tomcat:  ## 单个数据库连接池,而且得写上tomcat的属性配置才可以生效
      initial-size: 1
      max-active: 5
      ## when pool sweeper is enabled, extra idle connection will be closed
      max-idle: 5
      ## when idle connection > min-idle, poolSweeper will start to close
      min-idle: 1

注意，这里把具体tomcat数据库连接池的配置属性放到了spring.datasource.tomcat属性下面，这样才可以生效。

源码解析

spring-boot-autoconfigure-1.5.9.RELEASE-sources.jar!/org/springframework/boot/autoconfigure/jdbc/DataSourceAutoConfiguration.java

    @Configuration
    @Conditional(PooledDataSourceCondition.class)
    @ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
    @Import({ DataSourceConfiguration.Tomcat.class, DataSourceConfiguration.Hikari.class,
            DataSourceConfiguration.Dbcp.class, DataSourceConfiguration.Dbcp2.class,
            DataSourceConfiguration.Generic.class })
    @SuppressWarnings("deprecation")
    protected static class PooledDataSourceConfiguration {

    }

DataSourceConfiguration.Tomcat

spring-boot-autoconfigure-1.5.9.RELEASE-sources.jar!/org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration.java

    /**
     * Tomcat Pool DataSource configuration.
     */
    @ConditionalOnClass(org.apache.tomcat.jdbc.pool.DataSource.class)
    @ConditionalOnProperty(name = "spring.datasource.type", havingValue = "org.apache.tomcat.jdbc.pool.DataSource", matchIfMissing = true)
    static class Tomcat extends DataSourceConfiguration {

        @Bean
        @ConfigurationProperties(prefix = "spring.datasource.tomcat")
        public org.apache.tomcat.jdbc.pool.DataSource dataSource(
                DataSourceProperties properties) {
            org.apache.tomcat.jdbc.pool.DataSource dataSource = createDataSource(
                    properties, org.apache.tomcat.jdbc.pool.DataSource.class);
            DatabaseDriver databaseDriver = DatabaseDriver
                    .fromJdbcUrl(properties.determineUrl());
            String validationQuery = databaseDriver.getValidationQuery();
            if (validationQuery != null) {
                dataSource.setTestOnBorrow(true);
                dataSource.setValidationQuery(validationQuery);
            }
            return dataSource;
        }

    }

可以看到这里的DataSourceProperties仅仅只有spring.datasource直接属性的配置，比如url，username，password，driverClassName。tomcat的具体属性都没有。

createDataSource

protected <T> T createDataSource(DataSourceProperties properties,
            Class<? extends DataSource> type) {
        return (T) properties.initializeDataSourceBuilder().type(type).build();
    }

直接createDataSource出来的org.apache.tomcat.jdbc.pool.DataSource的PoolProperties也是默认的配置

ConfigurationProperties

具体的魔力就在于@ConfigurationProperties(prefix = "spring.datasource.tomcat")这段代码，它在spring容器构造好代理bean返回之前会将spring.datasource.tomcat指定的属性设置到org.apache.tomcat.jdbc.pool.DataSource

spring-boot-1.5.9.RELEASE-sources.jar!/org/springframework/boot/context/properties/ConfigurationPropertiesBindingPostProcessor.java

private void postProcessBeforeInitialization(Object bean, String beanName,
            ConfigurationProperties annotation) {
        Object target = bean;
        PropertiesConfigurationFactory<Object> factory = new PropertiesConfigurationFactory<Object>(
                target);
        factory.setPropertySources(this.propertySources);
        factory.setValidator(determineValidator(bean));
        // If no explicit conversion service is provided we add one so that (at least)
        // comma-separated arrays of convertibles can be bound automatically
        factory.setConversionService(this.conversionService == null
                ? getDefaultConversionService() : this.conversionService);
        if (annotation != null) {
            factory.setIgnoreInvalidFields(annotation.ignoreInvalidFields());
            factory.setIgnoreUnknownFields(annotation.ignoreUnknownFields());
            factory.setExceptionIfInvalid(annotation.exceptionIfInvalid());
            factory.setIgnoreNestedProperties(annotation.ignoreNestedProperties());
            if (StringUtils.hasLength(annotation.prefix())) {
                factory.setTargetName(annotation.prefix());
            }
        }
        try {
            factory.bindPropertiesToTarget();
        }
        catch (Exception ex) {
            String targetClass = ClassUtils.getShortName(target.getClass());
            throw new BeanCreationException(beanName, "Could not bind properties to "
                    + targetClass + " (" + getAnnotationDetails(annotation) + ")", ex);
        }
    }

注意，这里的annotation就是@ConfigurationProperties(prefix = "spring.datasource.tomcat")，它的prefix是spring.datasource.tomcat
PropertiesConfigurationFactory的targetName就是spring.datasource.tomcat

PropertiesConfigurationFactory.bindPropertiesToTarget

spring-boot-1.5.9.RELEASE-sources.jar!/org/springframework/boot/bind/PropertiesConfigurationFactory.java

    public void bindPropertiesToTarget() throws BindException {
        Assert.state(this.propertySources != null, "PropertySources should not be null");
        try {
            if (logger.isTraceEnabled()) {
                logger.trace("Property Sources: " + this.propertySources);

            }
            this.hasBeenBound = true;
            doBindPropertiesToTarget();
        }
        catch (BindException ex) {
            if (this.exceptionIfInvalid) {
                throw ex;
            }
            PropertiesConfigurationFactory.logger
                    .error("Failed to load Properties validation bean. "
                            + "Your Properties may be invalid.", ex);
        }
    }

委托给doBindPropertiesToTarget方法

PropertiesConfigurationFactory.doBindPropertiesToTarget

private void doBindPropertiesToTarget() throws BindException {
        RelaxedDataBinder dataBinder = (this.targetName != null
                ? new RelaxedDataBinder(this.target, this.targetName)
                : new RelaxedDataBinder(this.target));
        if (this.validator != null
                && this.validator.supports(dataBinder.getTarget().getClass())) {
            dataBinder.setValidator(this.validator);
        }
        if (this.conversionService != null) {
            dataBinder.setConversionService(this.conversionService);
        }
        dataBinder.setAutoGrowCollectionLimit(Integer.MAX_VALUE);
        dataBinder.setIgnoreNestedProperties(this.ignoreNestedProperties);
        dataBinder.setIgnoreInvalidFields(this.ignoreInvalidFields);
        dataBinder.setIgnoreUnknownFields(this.ignoreUnknownFields);
        customizeBinder(dataBinder);
        Iterable<String> relaxedTargetNames = getRelaxedTargetNames();
        Set<String> names = getNames(relaxedTargetNames);
        PropertyValues propertyValues = getPropertySourcesPropertyValues(names,
                relaxedTargetNames);
        dataBinder.bind(propertyValues);
        if (this.validator != null) {
            dataBinder.validate();
        }
        checkForBindingErrors(dataBinder);
    }

这里借助RelaxedDataBinder.bind方法

getRelaxedTargetNames

    private Iterable<String> getRelaxedTargetNames() {
        return (this.target != null && StringUtils.hasLength(this.targetName)
                ? new RelaxedNames(this.targetName) : null);
    }

这里new了一个RelaxedNames，可以识别多个变量的变种

RelaxedNames

spring-boot-1.5.9.RELEASE-sources.jar!/org/springframework/boot/bind/RelaxedNames.java

    private void initialize(String name, Set<String> values) {
        if (values.contains(name)) {
            return;
        }
        for (Variation variation : Variation.values()) {
            for (Manipulation manipulation : Manipulation.values()) {
                String result = name;
                result = manipulation.apply(result);
                result = variation.apply(result);
                values.add(result);
                initialize(result, values);
            }
        }
    }

    /**
     * Name variations.
     */
    enum Variation {

        NONE {

            @Override
            public String apply(String value) {
                return value;
            }

        },

        LOWERCASE {

            @Override
            public String apply(String value) {
                return value.isEmpty() ? value : value.toLowerCase();
            }

        },

        UPPERCASE {

            @Override
            public String apply(String value) {
                return value.isEmpty() ? value : value.toUpperCase();
            }

        };

        public abstract String apply(String value);

    }

即支持org.springframework.boot.bind.RelaxedNames@6ef81f31[name=spring.datasource.tomcat,values=[spring.datasource.tomcat, spring_datasource_tomcat, springDatasourceTomcat, springdatasourcetomcat, SPRING.DATASOURCE.TOMCAT, SPRING_DATASOURCE_TOMCAT, SPRINGDATASOURCETOMCAT]]这7中配置的写法

getPropertySourcesPropertyValues

    private PropertyValues getPropertySourcesPropertyValues(Set<String> names,
            Iterable<String> relaxedTargetNames) {
        PropertyNamePatternsMatcher includes = getPropertyNamePatternsMatcher(names,
                relaxedTargetNames);
        return new PropertySourcesPropertyValues(this.propertySources, names, includes,
                this.resolvePlaceholders);
    }

这个方法会把spring.datasource.tomact底下的属性配置拉取到PropertyValues对象里头

RelaxedDataBinder.bind

spring-boot-1.5.9.RELEASE-sources.jar!/org/springframework/boot/bind/RelaxedDataBinder.java的bind方法调用的是父类的方法
spring-context-4.3.13.RELEASE-sources.jar!/org/springframework/validation/DataBinder.java

    /**
     * Bind the given property values to this binder's target.
     * <p>This call can create field errors, representing basic binding
     * errors like a required field (code "required"), or type mismatch
     * between value and bean property (code "typeMismatch").
     * <p>Note that the given PropertyValues should be a throwaway instance:
     * For efficiency, it will be modified to just contain allowed fields if it
     * implements the MutablePropertyValues interface; else, an internal mutable
     * copy will be created for this purpose. Pass in a copy of the PropertyValues
     * if you want your original instance to stay unmodified in any case.
     * @param pvs property values to bind
     * @see #doBind(org.springframework.beans.MutablePropertyValues)
     */
    public void bind(PropertyValues pvs) {
        MutablePropertyValues mpvs = (pvs instanceof MutablePropertyValues) ?
                (MutablePropertyValues) pvs : new MutablePropertyValues(pvs);
        doBind(mpvs);
    }

    /**
     * Actual implementation of the binding process, working with the
     * passed-in MutablePropertyValues instance.
     * @param mpvs the property values to bind,
     * as MutablePropertyValues instance
     * @see #checkAllowedFields
     * @see #checkRequiredFields
     * @see #applyPropertyValues
     */
    protected void doBind(MutablePropertyValues mpvs) {
        checkAllowedFields(mpvs);
        checkRequiredFields(mpvs);
        applyPropertyValues(mpvs);
    }

    /**
     * Apply given property values to the target object.
     * <p>Default implementation applies all of the supplied property
     * values as bean property values. By default, unknown fields will
     * be ignored.
     * @param mpvs the property values to be bound (can be modified)
     * @see #getTarget
     * @see #getPropertyAccessor
     * @see #isIgnoreUnknownFields
     * @see #getBindingErrorProcessor
     * @see BindingErrorProcessor#processPropertyAccessException
     */
    protected void applyPropertyValues(MutablePropertyValues mpvs) {
        try {
            // Bind request parameters onto target object.
            getPropertyAccessor().setPropertyValues(mpvs, isIgnoreUnknownFields(), isIgnoreInvalidFields());
        }
        catch (PropertyBatchUpdateException ex) {
            // Use bind error processor to create FieldErrors.
            for (PropertyAccessException pae : ex.getPropertyAccessExceptions()) {
                getBindingErrorProcessor().processPropertyAccessException(pae, getInternalBindingResult());
            }
        }
    }

    /**
     * Return the underlying PropertyAccessor of this binder's BindingResult.
     */
    protected ConfigurablePropertyAccessor getPropertyAccessor() {
        return getInternalBindingResult().getPropertyAccessor();
    }

最后通过getPropertyAccessor()来设置，这个propertyAccessor就是org.springframework.boot.bind.RelaxedDataBinder$RelaxedBeanWrapper: wrapping object [org.apache.tomcat.jdbc.pool.DataSource@6a84bc2a]，也就包装的org.apache.tomcat.jdbc.pool.DataSource

AbstractPropertyAccessor.setPropertyValues

spring-beans-4.3.13.RELEASE-sources.jar!/org/springframework/beans/AbstractPropertyAccessor.java

    @Override
    public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
            throws BeansException {

        List<PropertyAccessException> propertyAccessExceptions = null;
        List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
                ((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
        for (PropertyValue pv : propertyValues) {
            try {
                // This method may throw any BeansException, which won't be caught
                // here, if there is a critical failure such as no matching field.
                // We can attempt to deal only with less serious exceptions.
                setPropertyValue(pv);
            }
            catch (NotWritablePropertyException ex) {
                if (!ignoreUnknown) {
                    throw ex;
                }
                // Otherwise, just ignore it and continue...
            }
            catch (NullValueInNestedPathException ex) {
                if (!ignoreInvalid) {
                    throw ex;
                }
                // Otherwise, just ignore it and continue...
            }
            catch (PropertyAccessException ex) {
                if (propertyAccessExceptions == null) {
                    propertyAccessExceptions = new LinkedList<PropertyAccessException>();
                }
                propertyAccessExceptions.add(ex);
            }
        }

        // If we encountered individual exceptions, throw the composite exception.
        if (propertyAccessExceptions != null) {
            PropertyAccessException[] paeArray =
                    propertyAccessExceptions.toArray(new PropertyAccessException[propertyAccessExceptions.size()]);
            throw new PropertyBatchUpdateException(paeArray);
        }
    }

    @Override
    public void setPropertyValue(PropertyValue pv) throws BeansException {
        PropertyTokenHolder tokens = (PropertyTokenHolder) pv.resolvedTokens;
        if (tokens == null) {
            String propertyName = pv.getName();
            AbstractNestablePropertyAccessor nestedPa;
            try {
                nestedPa = getPropertyAccessorForPropertyPath(propertyName);
            }
            catch (NotReadablePropertyException ex) {
                throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
                        "Nested property in path '" + propertyName + "' does not exist", ex);
            }
            tokens = getPropertyNameTokens(getFinalPath(nestedPa, propertyName));
            if (nestedPa == this) {
                pv.getOriginalPropertyValue().resolvedTokens = tokens;
            }
            nestedPa.setPropertyValue(tokens, pv);
        }
        else {
            setPropertyValue(tokens, pv);
        }
    }

这里的nestedPa.setPropertyValue(tokens, pv);真正把spring.datasource.tomcat的属性值设置进去
这里的nestedPa就是org.springframework.boot.bind.RelaxedDataBinder$RelaxedBeanWrapper: wrapping object [org.apache.tomcat.jdbc.pool.DataSource@6a84bc2a]
最后是调用AbstractNestablePropertyAccessor.processLocalProperty

AbstractNestablePropertyAccessor.processLocalProperty

spring-beans-4.3.13.RELEASE-sources.jar!/org/springframework/beans/AbstractNestablePropertyAccessor.java

private void processLocalProperty(PropertyTokenHolder tokens, PropertyValue pv) {
        PropertyHandler ph = getLocalPropertyHandler(tokens.actualName);
        if (ph == null || !ph.isWritable()) {
            if (pv.isOptional()) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Ignoring optional value for property '" + tokens.actualName +
                            "' - property not found on bean class [" + getRootClass().getName() + "]");
                }
                return;
            }
            else {
                throw createNotWritablePropertyException(tokens.canonicalName);
            }
        }

        Object oldValue = null;
        try {
            Object originalValue = pv.getValue();
            Object valueToApply = originalValue;
            if (!Boolean.FALSE.equals(pv.conversionNecessary)) {
                if (pv.isConverted()) {
                    valueToApply = pv.getConvertedValue();
                }
                else {
                    if (isExtractOldValueForEditor() && ph.isReadable()) {
                        try {
                            oldValue = ph.getValue();
                        }
                        catch (Exception ex) {
                            if (ex instanceof PrivilegedActionException) {
                                ex = ((PrivilegedActionException) ex).getException();
                            }
                            if (logger.isDebugEnabled()) {
                                logger.debug("Could not read previous value of property '" +
                                        this.nestedPath + tokens.canonicalName + "'", ex);
                            }
                        }
                    }
                    valueToApply = convertForProperty(
                            tokens.canonicalName, oldValue, originalValue, ph.toTypeDescriptor());
                }
                pv.getOriginalPropertyValue().conversionNecessary = (valueToApply != originalValue);
            }
            ph.setValue(this.wrappedObject, valueToApply);
        }
        catch (TypeMismatchException ex) {
            throw ex;
        }
        catch (InvocationTargetException ex) {
            PropertyChangeEvent propertyChangeEvent = new PropertyChangeEvent(
                    this.rootObject, this.nestedPath + tokens.canonicalName, oldValue, pv.getValue());
            if (ex.getTargetException() instanceof ClassCastException) {
                throw new TypeMismatchException(propertyChangeEvent, ph.getPropertyType(), ex.getTargetException());
            }
            else {
                Throwable cause = ex.getTargetException();
                if (cause instanceof UndeclaredThrowableException) {
                    // May happen e.g. with Groovy-generated methods
                    cause = cause.getCause();
                }
                throw new MethodInvocationException(propertyChangeEvent, cause);
            }
        }
        catch (Exception ex) {
            PropertyChangeEvent pce = new PropertyChangeEvent(
                    this.rootObject, this.nestedPath + tokens.canonicalName, oldValue, pv.getValue());
            throw new MethodInvocationException(pce, ex);
        }
    }

它使其是使用class org.springframework.beans.BeanWrapperImpl$BeanPropertyHandler来设置

BeanWrapperImpl$BeanPropertyHandler.setValue

spring-beans-4.3.13.RELEASE-sources.jar!/org/springframework/beans/BeanWrapperImpl.java

        @Override
        public void setValue(final Object object, Object valueToApply) throws Exception {
            final Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ?
                    ((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :
                    this.pd.getWriteMethod());
            if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) {
                if (System.getSecurityManager() != null) {
                    AccessController.doPrivileged(new PrivilegedAction<Object>() {
                        @Override
                        public Object run() {
                            writeMethod.setAccessible(true);
                            return null;
                        }
                    });
                }
                else {
                    writeMethod.setAccessible(true);
                }
            }
            final Object value = valueToApply;
            if (System.getSecurityManager() != null) {
                try {
                    AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                        @Override
                        public Object run() throws Exception {
                            writeMethod.invoke(object, value);
                            return null;
                        }
                    }, acc);
                }
                catch (PrivilegedActionException ex) {
                    throw ex.getException();
                }
            }
            else {
                writeMethod.invoke(getWrappedInstance(), value);
            }
        }
    }

这里利用反射找出setXXX方法(比如setMaxActive)，然后设置进去

多数据源的配置

上面的配置对于单数据源来说是没有问题的，对于多数据源，则配置如下

@Configuration
public class MasterDatasourceConfig {

    @Bean("masterDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.master")
    public DataSource masterDataSource() {
        return DataSourceBuilder.create().build();
    }
}    

注意，这里要添加ConfigurationProperties注入tomcat jdbc pool的额外设置

spring:
  datasource:
    master:
      type: org.apache.tomcat.jdbc.pool.DataSource
      driver-class-name: org.postgresql.Driver
      url: jdbc:postgresql://192.168.99.100:5432/postgres?connectTimeout=6000&socketTimeout=6000
      username: postgres
      password: postgres
      jmx-enabled: true
#    tomcat: ## 多数据源的话,这里要去掉tomcat,通通放在数据源前缀下面
      initial-size: 1
      max-active: 5
      ## when pool sweeper is enabled, extra idle connection will be closed
      max-idle: 5
      ## when idle connection > min-idle, poolSweeper will start to close
      min-idle: 1

原先tomcat的配置都要放在数据源前缀的底下，放在spring.datasource.tomcat或者spring.datasource.master.tomcat底下均无法生效。

小结

spirngboot的自动配置是挺方便的，但是在实际应用的场景下还需要了解底层机制才可以，否则容易出来配置假象，以为配置对了，实际没生效。

doc

• boot-features-configure-datasource