@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
1、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;
}2、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();
}以上为个人经验，希望能给大家一个参考，也希望大家多多支持编程网。
