Merge pull request lightbend#708 from bbaldino/parse_app_overrides

Split out a helper method for parsing only application overrides

Author: havocp

config/src/main/java/com/typesafe/config/ConfigFactory.java

@@ -8,8 +8,10 @@
 
 import java.io.File;
 import java.io.Reader;
+import java.net.MalformedURLException;
 import java.net.URL;
 import java.util.Map;
+import java.util.Optional;
 import java.util.Properties;
 import java.util.concurrent.Callable;
 
@@ -1090,6 +1092,89 @@ public static Config parseResourcesAnySyntax(String resourceBasename) {
         return parseResourcesAnySyntax(resourceBasename, ConfigParseOptions.defaults());
     }
 
+    /**
+     * Parse only any application replacement (specified by one of config.{resource,file,url}), returning
+     * an empty Config if no overrides were set.
+     *
+     * @since 1.4.1
+     *
+     * @return a {@link java.util.Optional} containing any specified replacement, or {@link Optional#empty()}
+     * if none was specified.
+     */
+    public static java.util.Optional<Config> parseApplicationReplacement() {
+        return parseApplicationReplacement(ConfigParseOptions.defaults());
+    }
+
+    /**
+     * Like {@link #parseApplicationReplacement()} but allows you to specify a class loader
+     * ti yse rather than the current context class loader.
+     *
+     * @since 1.4.1
+     *
+     * @param loader the class loader
+     * @return a {@link java.util.Optional} containing any specified replacement, or {@link Optional#empty()}
+     * if none was specified.
+     */
+    public static java.util.Optional<Config> parseApplicationReplacement(ClassLoader loader) {
+        return parseApplicationReplacement(ConfigParseOptions.defaults().setClassLoader(loader));
+    }
+
+    /**
+     * Like {@link #parseApplicationReplacement()} but allows you to specify parse options.
+     *
+     * @since 1.4.1
+     *
+     * @param parseOptions parse options
+     * @return a {@link java.util.Optional} containing any specified replacement, or {@link Optional#empty()}
+     * if none was specified.
+     */
+    public static java.util.Optional<Config> parseApplicationReplacement(ConfigParseOptions parseOptions) {
+        ensureClassLoader(parseOptions, "parseApplicationReplacement");
+        ClassLoader loader = parseOptions.getClassLoader();
+
+        int specified = 0;
+
+        // override application.conf with config.file, config.resource,
+        // config.url if requested.
+        String resource = System.getProperty("config.resource");
+        if (resource != null)
+            specified += 1;
+        String file = System.getProperty("config.file");
+        if (file != null)
+            specified += 1;
+        String url = System.getProperty("config.url");
+        if (url != null)
+            specified += 1;
+
+        if (specified == 0) {
+            return java.util.Optional.empty();
+        } else if (specified > 1) {
+            throw new ConfigException.Generic("You set more than one of config.file='" + file
+                + "', config.url='" + url + "', config.resource='" + resource
+                + "'; don't know which one to use!");
+        } else {
+            // the override file/url/resource MUST be present or it's an error
+            ConfigParseOptions overrideOptions = parseOptions.setAllowMissing(false);
+            if (resource != null) {
+                if (resource.startsWith("/"))
+                    resource = resource.substring(1);
+                // this deliberately does not parseResourcesAnySyntax; if
+                // people want that they can use an include statement.
+                return java.util.Optional.of(ConfigFactory.parseResources(loader, resource, overrideOptions));
+            } else if (file != null) {
+                return java.util.Optional.of(ConfigFactory.parseFile(new File(file), overrideOptions));
+            } else {
+                try {
+                    return java.util.Optional.of(ConfigFactory.parseURL(new URL(url), overrideOptions));
+                } catch (MalformedURLException e) {
+                    throw new ConfigException.Generic("Bad URL in config.url system property: '"
+                        + url + "': " + e.getMessage(), e);
+                }
+            }
+        }
+
+    }
+
     /**
      * Parses a string (which should be valid HOCON or JSON by default, or
      * the syntax specified in the options otherwise).

config/src/main/java/com/typesafe/config/DefaultConfigLoadingStrategy.java

@@ -1,9 +1,5 @@
 package com.typesafe.config;
 
-import java.io.File;
-import java.net.MalformedURLException;
-import java.net.URL;
-
 /**
  * Default config loading strategy. Able to load resource, file or URL.
  * Behavior may be altered by defining one of VM properties
@@ -12,51 +8,7 @@
 public class DefaultConfigLoadingStrategy implements ConfigLoadingStrategy {
     @Override
     public Config parseApplicationConfig(ConfigParseOptions parseOptions) {
-        ClassLoader loader = parseOptions.getClassLoader();
-        if (loader == null)
-            throw new ConfigException.BugOrBroken(
-                    "ClassLoader should have been set here; bug in ConfigFactory. "
-                            + "(You can probably work around this bug by passing in a class loader or calling currentThread().setContextClassLoader() though.)");
-
-        int specified = 0;
-
-        // override application.conf with config.file, config.resource,
-        // config.url if requested.
-        String resource = System.getProperty("config.resource");
-        if (resource != null)
-            specified += 1;
-        String file = System.getProperty("config.file");
-        if (file != null)
-            specified += 1;
-        String url = System.getProperty("config.url");
-        if (url != null)
-            specified += 1;
-
-        if (specified == 0) {
-            return ConfigFactory.parseResourcesAnySyntax("application", parseOptions);
-        } else if (specified > 1) {
-            throw new ConfigException.Generic("You set more than one of config.file='" + file
-                                                      + "', config.url='" + url + "', config.resource='" + resource
-                                                      + "'; don't know which one to use!");
-        } else {
-            // the override file/url/resource MUST be present or it's an error
-            ConfigParseOptions overrideOptions = parseOptions.setAllowMissing(false);
-            if (resource != null) {
-                if (resource.startsWith("/"))
-                    resource = resource.substring(1);
-                // this deliberately does not parseResourcesAnySyntax; if
-                // people want that they can use an include statement.
-                return ConfigFactory.parseResources(loader, resource, overrideOptions);
-            } else if (file != null) {
-                return ConfigFactory.parseFile(new File(file), overrideOptions);
-            } else {
-                try {
-                    return ConfigFactory.parseURL(new URL(url), overrideOptions);
-                } catch (MalformedURLException e) {
-                    throw new ConfigException.Generic("Bad URL in config.url system property: '"
-                                                              + url + "': " + e.getMessage(), e);
-                }
-            }
-        }
+        return ConfigFactory.parseApplicationReplacement(parseOptions)
+            .orElseGet(() -> ConfigFactory.parseResourcesAnySyntax("application", parseOptions));
     }
 }