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@Value注入boolean设置默认值
问题描述
Springboot 中读取配置文件
test：业务代码如下
@Value("${test:true}")private boolean test;报错如下
nested exception is org.springframework.beans.TypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'boolean'; nested exception is java.lang.IllegalArgumentException: Invalid boolean value []
问题分析
根据报错可知，主要问题在于 注入时 test 的值是 String 类型，无法转换成 boolean 类型。
@Value("${test:true}")private String test;于是更改了接收类型，看看获取到的值是否是 true，结果发现 test 值为 “”，而不是设置的默认值
解决方案
报错问题在于只要配置文件中有 test: 所以系统就默认 test 为 “” 而不是按照我所设想的为空所以默认值为 true。
直接删除配置文件中的 test: 即可正常启动。
@Value 源码阅读
在排查问题的过程中也粗略的跟读了一下源码
//org.springframework.beans.TypeConverterSupport#doConvert()private <T> T doConvert(Object value, Class<T> requiredType, MethodParameter methodParam, Field field) throws TypeMismatchException { try { return field != null ? this.typeConverterDelegate.convertIfNecessary(value, requiredType, field) : this.typeConverterDelegate.convertIfNecessary(value, requiredType, methodParam); } catch (ConverterNotFoundException var6) { throw new ConversionNotSupportedException(value, requiredType, var6); } catch (ConversionException var7) { throw new TypeMismatchException(value, requiredType, var7); } catch (IllegalStateException var8) { throw new ConversionNotSupportedException(value, requiredType, var8); } catch (IllegalArgumentException var9) { // 最终异常从这里抛出 throw new TypeMismatchException(value, requiredType, var9); } }最终赋值在
//org.springframework.beans.TypeConverterDelegate#doConvertTextValue()private Object doConvertTextValue(Object oldValue, String newTextValue, PropertyEditor editor) { try { editor.setValue(oldValue); } catch (Exception var5) { if (logger.isDebugEnabled()) { logger.debug("PropertyEditor [" + editor.getClass().getName() + "] does not support setValue call", var5); } } // 此处发现 newTextValue 为 "" editor.setAsText(newTextValue); return editor.getValue();}接下来就是如何将 字符串 true 转换为 boolean 的具体代码：
// org.springframework.beans.propertyeditors.CustomBooleanEditor#setAsText() public void setAsText(String text) throws IllegalArgumentException { String input = text != null ? text.trim() : null; if (this.allowEmpty && !StringUtils.hasLength(input)) { this.setValue((Object)null); } else if (this.trueString != null && this.trueString.equalsIgnoreCase(input)) { this.setValue(Boolean.TRUE); } else if (this.falseString != null && this.falseString.equalsIgnoreCase(input)) { this.setValue(Boolean.FALSE); } else if (this.trueString != null || !"true".equalsIgnoreCase(input) && !"on".equalsIgnoreCase(input) && !"yes".equalsIgnoreCase(input) && !"1".equals(input)) { if (this.falseString != null || !"false".equalsIgnoreCase(input) && !"off".equalsIgnoreCase(input) && !"no".equalsIgnoreCase(input) && !"0".equals(input)) { throw new IllegalArgumentException("Invalid boolean value [" + text + "]"); } this.setValue(Boolean.FALSE); } else { this.setValue(Boolean.TRUE); } }tips：windows 中使用 IDEA 去查找类可以使用 ctrl + shift +alt +N的快捷键组合去查询，mac 系统则是 commond + O
Spring解析@Value
初始化PropertyPlaceholderHelper对象
protected String placeholderPrefix = "${"; protected String placeholderSuffix = "}"; @Nullable protected String valueSeparator = ":"; private static final Map<String, String> wellKnownSimplePrefixes = new HashMap<>(4); static { wellKnownSimplePrefixes.put("}", "{"); wellKnownSimplePrefixes.put("]", "["); wellKnownSimplePrefixes.put(")", "("); } public PropertyPlaceholderHelper(String placeholderPrefix, String placeholderSuffix, @Nullable String valueSeparator, boolean ignoreUnresolvablePlaceholders) { Assert.notNull(placeholderPrefix, "'placeholderPrefix' must not be null"); Assert.notNull(placeholderSuffix, "'placeholderSuffix' must not be null"); //默认值${ this.placeholderPrefix = placeholderPrefix; //默认值} this.placeholderSuffix = placeholderSuffix; String simplePrefixForSuffix = wellKnownSimplePrefixes.get(this.placeholderSuffix); //当前缀为空或跟定义的不匹配，取传入的前缀 if (simplePrefixForSuffix != null && this.placeholderPrefix.endsWith(simplePrefixForSuffix)) { this.simplePrefix = simplePrefixForSuffix; } else { this.simplePrefix = this.placeholderPrefix; } //默认值: this.valueSeparator = valueSeparator; this.ignoreUnresolvablePlaceholders = ignoreUnresolvablePlaceholders; }解析@Value
protected String parseStringValue( String value, PlaceholderResolver placeholderResolver, Set<String> visitedPlaceholders) { StringBuilder result = new StringBuilder(value); //是否包含前缀，返回第一个前缀的开始index int startIndex = value.indexOf(this.placeholderPrefix); while (startIndex != -1) { //找到最后一个后缀的index int endIndex = findPlaceholderEndIndex(result, startIndex); if (endIndex != -1) { //去掉前缀后缀，取出里面的字符串 String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex); String originalPlaceholder = placeholder; if (!visitedPlaceholders.add(originalPlaceholder)) { throw new IllegalArgumentException( "Circular placeholder reference '" + originalPlaceholder + "' in property definitions"); } // 递归判断是否存在占位符，可以这样写${acm.endpoint:${address.server.domain:}} placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders); // 根据key获取对应的值 String propVal = placeholderResolver.resolvePlaceholder(placeholder); // 值不存在，但存在默认值的分隔符 if (propVal == null && this.valueSeparator != null) { // 获取默认值的索引 int separatorIndex = placeholder.indexOf(this.valueSeparator); if (separatorIndex != -1) { // 切掉默认值的字符串 String actualPlaceholder = placeholder.substring(0, separatorIndex); // 切出默认值 String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length()); // 根据新的key获取对应的值 propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder); // 如果值不存在，则把默认值赋值给当前值 if (propVal == null) { propVal = defaultValue; } } } // 如果当前值不为NULL if (propVal != null) { // 递归获取存在占位符的值信息 propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders); // 替换占位符 result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal); if (logger.isTraceEnabled()) { logger.trace("Resolved placeholder '" + placeholder + "'"); } startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length()); } else if (this.ignoreUnresolvablePlaceholders) { // Proceed with unprocessed value. startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length()); } else { throw new IllegalArgumentException("Could not resolve placeholder '" + placeholder + "'" + " in value \"" + value + "\""); } visitedPlaceholders.remove(originalPlaceholder); } else { startIndex = -1; } } return result.toString(); }读到这里，这篇“Springboot @Value注入boolean如何设置默认值”文章已经介绍完毕，想要掌握这篇文章的知识点还需要大家自己动手实践使用过才能领会，如果想了解更多相关内容的文章，欢迎关注编程网行业资讯频道。
