com.cloudera.director.aws.common.PropertyResolvers.java Source code

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Here is the source code for com.cloudera.director.aws.common.PropertyResolvers.java

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// (c) Copyright 2015 Cloudera, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.cloudera.director.aws.common;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.collect.ImmutableMap;

import java.io.IOException;
import java.util.Map;

import org.springframework.core.env.MapPropertySource;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertyResolver;
import org.springframework.core.env.PropertySource;
import org.springframework.core.env.PropertySourcesPropertyResolver;
import org.springframework.core.io.support.ResourcePropertySource;

/**
 * A convenience class for creating property resolvers.
 */
public final class PropertyResolvers {

    private static final String BUILT_IN_NAME = "built-in";
    private static final String CUSTOM_NAME_PREFIX = "custom";

    private PropertyResolvers() {
    }

    /**
     * Creates a new property resolver with no properties.
     *
     * @return new property resolver
     */
    public static PropertyResolver newEmptyPropertyResolver() {
        return new PropertySourcesPropertyResolver(new MutablePropertySources());
    }

    /**
     * Creates a new property resolver that gets properties from the given map.
     *
     * @param m property map
     * @return new property resolver
     * @throws NullPointerException if the map is null
     */
    public static PropertyResolver newMapPropertyResolver(Map<String, String> m) {
        checkNotNull(m, "map is null");
        MutablePropertySources sources = new MutablePropertySources();
        sources.addFirst(new MapPropertySource("map", ImmutableMap.<String, Object>copyOf(m)));
        return new PropertySourcesPropertyResolver(sources);
    }

    /**
     * Creates a property resolver that pulls from multiple property resource
     * locations. The first "built-in" location must be successfully loaded, but
     * all other "custom" locations may fail to load.
     *
     * @param builtInResourceLocation lowest precedence, required resource
     *                                location for properties
     * @param customResourceLocations additional resource locations for
     *                                properties, in increasing order of precedence
     * @return new property resolver
     * @throws IOException          if the built-in resource location could not be loaded
     * @throws NullPointerException if any resource location is null
     */
    public static PropertyResolver newMultiResourcePropertyResolver(String builtInResourceLocation,
            String... customResourceLocations) throws IOException {
        return newMultiResourcePropertyResolver(true, builtInResourceLocation, customResourceLocations);
    }

    /**
     * Creates a property resolver that pulls from multiple property resource
     * locations. The first "built-in" location must be successfully loaded, but
     * all other "custom" locations must load only if {code}allowMissing{code} is
     * false.
     *
     * @param allowMissing            true to allow custom resource locations to fail to load
     * @param builtInResourceLocation lowest precedence, required resource
     *                                location for properties
     * @param customResourceLocations additional resource locations for
     *                                properties, in increasing order of precedence
     * @return new property resolver
     * @throws IOException          if the built-in resource location could not be loaded,
     *                              or if {code}allowMissing{code} is false and any custom resource location
     *                              fails to load
     * @throws NullPointerException if any resource location is null
     */
    public static PropertyResolver newMultiResourcePropertyResolver(boolean allowMissing,
            String builtInResourceLocation, String... customResourceLocations) throws IOException {
        MutablePropertySources sources = new MutablePropertySources();
        checkNotNull(builtInResourceLocation, "builtInResourceLocation is null");
        sources.addLast(buildPropertySource(BUILT_IN_NAME, builtInResourceLocation, false));
        String lastname = BUILT_IN_NAME;
        int customCtr = 1;
        for (String loc : customResourceLocations) {
            checkNotNull(loc, "customResourceLocations[" + (customCtr - 1) + "] is null");
            String thisname = CUSTOM_NAME_PREFIX + customCtr++;
            PropertySource source = buildPropertySource(thisname, loc, allowMissing);
            if (source != null) {
                sources.addBefore(lastname, source);
                lastname = thisname;
            }
        }

        return new PropertySourcesPropertyResolver(sources);
    }

    private static PropertySource buildPropertySource(String name, String loc, boolean allowMissing)
            throws IOException {
        try {
            return new ResourcePropertySource(name, loc, PropertyResolvers.class.getClassLoader());
        } catch (IOException e) {
            if (allowMissing) {
                return null;
            }
            throw new IOException("Unable to load " + name + " properties from " + loc, e);
        }
    }

}