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90 lines
2.1 KiB
90 lines
2.1 KiB
# Spring SystemPropertyUtils
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- spring 中获取系统属性的工具类
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- 内部属性
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```java
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/**
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*
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* Prefix for system property placeholders: "${".
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* 前缀占位符
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* */
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public static final String PLACEHOLDER_PREFIX = "${";
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/**
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* Suffix for system property placeholders: "}".
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* 后缀占位符
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* */
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public static final String PLACEHOLDER_SUFFIX = "}";
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/**
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* Value separator for system property placeholders: ":".
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* 值分割符号
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* */
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public static final String VALUE_SEPARATOR = ":";
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/**
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* 占位符解析类
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*/
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private static final PropertyPlaceholderHelper strictHelper =
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new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, false);
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/**
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* 占位符解析类
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*/
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private static final PropertyPlaceholderHelper nonStrictHelper =
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new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, true);
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```
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## resolvePlaceholders
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- 解析属性
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时序图因为有递归所以看着有点长, 其核心方法最后会指向 PlaceholderResolver
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通过 PlaceholderResolver 获取属性值
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在 `SystemPropertyUtils` 内部有 `PlaceholderResolver ` 实现
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- 最终通过下面的类来获取具体的属性值
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```java
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private static class SystemPropertyPlaceholderResolver implements PropertyPlaceholderHelper.PlaceholderResolver {
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private final String text;
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public SystemPropertyPlaceholderResolver(String text) {
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this.text = text;
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}
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@Override
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@Nullable
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public String resolvePlaceholder(String placeholderName) {
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try {
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String propVal = System.getProperty(placeholderName);
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if (propVal == null) {
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// Fall back to searching the system environment.
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// 获取系统属性
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propVal = System.getenv(placeholderName);
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}
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return propVal;
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}
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catch (Throwable ex) {
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System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" +
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this.text + "] as system property: " + ex);
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return null;
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}
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}
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}
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``` |