com.google.auto.value.processor.TemplateVars Maven / Gradle / Ivy
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/*
* Copyright (C) 2014 Google, 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.google.auto.value.processor;
import com.google.common.base.Throwables;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.escapevelocity.Template;
import java.io.File;
import java.io.FileInputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.Map;
import java.util.TreeMap;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
/**
* A template and a set of variables to be substituted into that template. A concrete subclass of
* this class defines a set of fields that are template variables, and an implementation of the
* {@link #parsedTemplate()} method which is the template to substitute them into. Once the values
* of the fields have been assigned, the {@link #toText()} method returns the result of substituting
* them into the template.
*
* The subclass may be a direct subclass of this class or a more distant descendant. Every field
* in the starting class and its ancestors up to this class will be included. Fields cannot be
* static unless they are also final. They cannot be private, though they can be package-private if
* the class is in the same package as this class. They cannot be primitive or null, so that there
* is a clear indication when a field has not been set.
*
* @author Éamonn McManus
*/
abstract class TemplateVars {
abstract Template parsedTemplate();
private final ImmutableList fields;
TemplateVars() {
this.fields = getFields(getClass());
}
private static ImmutableList getFields(Class c) {
ImmutableList.Builder fieldsBuilder = ImmutableList.builder();
while (c != TemplateVars.class) {
addFields(fieldsBuilder, c.getDeclaredFields());
c = c.getSuperclass();
}
return fieldsBuilder.build();
}
private static void addFields(
ImmutableList.Builder fieldsBuilder, Field[] declaredFields) {
for (Field field : declaredFields) {
if (field.isSynthetic() || isStaticFinal(field)) {
continue;
}
if (Modifier.isPrivate(field.getModifiers())) {
throw new IllegalArgumentException("Field cannot be private: " + field);
}
if (Modifier.isStatic(field.getModifiers())) {
throw new IllegalArgumentException("Field cannot be static unless also final: " + field);
}
if (field.getType().isPrimitive()) {
throw new IllegalArgumentException("Field cannot be primitive: " + field);
}
fieldsBuilder.add(field);
}
}
/**
* Returns the result of substituting the variables defined by the fields of this class (a
* concrete subclass of TemplateVars) into the template returned by {@link #parsedTemplate()}.
*/
String toText() {
Map vars = toVars();
return parsedTemplate().evaluate(vars);
}
private Map toVars() {
Map vars = new TreeMap<>();
for (Field field : fields) {
Object value = fieldValue(field, this);
if (value == null) {
throw new IllegalArgumentException("Field cannot be null (was it set?): " + field);
}
Object old = vars.put(field.getName(), value);
if (old != null) {
throw new IllegalArgumentException("Two fields called " + field.getName() + "?!");
}
}
return ImmutableMap.copyOf(vars);
}
static Template parsedTemplateForResource(String resourceName) {
try {
return Template.parseFrom(resourceName, TemplateVars::readerFromResource);
} catch (UnsupportedEncodingException e) {
throw new AssertionError(e);
} catch (IOException | NullPointerException | IllegalStateException e) {
// https://github.com/google/auto/pull/439 says that we can get NullPointerException.
// https://github.com/google/auto/issues/715 says that we can get IllegalStateException
return retryParseAfterException(resourceName, e);
}
}
private static Template retryParseAfterException(String resourceName, Exception exception) {
try {
return Template.parseFrom(resourceName, TemplateVars::readerFromUrl);
} catch (IOException t) {
// Chain the original exception so we can see both problems.
Throwables.getRootCause(exception).initCause(t);
throw new AssertionError(exception);
}
}
private static Reader readerFromResource(String resourceName) {
InputStream in = TemplateVars.class.getResourceAsStream(resourceName);
if (in == null) {
throw new IllegalArgumentException("Could not find resource: " + resourceName);
}
return new InputStreamReader(in, StandardCharsets.UTF_8);
}
// This is an ugly workaround for https://bugs.openjdk.java.net/browse/JDK-6947916, as
// reported in https://github.com/google/auto/issues/365.
// The issue is that sometimes the InputStream returned by JarURLCollection.getInputStream()
// can be closed prematurely, which leads to an IOException saying "Stream closed".
// We catch all IOExceptions, and fall back on logic that opens the jar file directly and
// loads the resource from it. Since that doesn't use JarURLConnection, it shouldn't be
// susceptible to the same bug. We only use this as fallback logic rather than doing it always,
// because jars are memory-mapped by URLClassLoader, so loading a resource in the usual way
// through the getResourceAsStream should be a lot more efficient than reopening the jar.
private static Reader readerFromUrl(String resourceName) throws IOException {
URL resourceUrl = TemplateVars.class.getResource(resourceName);
InputStream in;
try {
if (resourceUrl.getProtocol().equalsIgnoreCase("file")) {
in = inputStreamFromFile(resourceUrl);
} else if (resourceUrl.getProtocol().equalsIgnoreCase("jar")) {
in = inputStreamFromJar(resourceUrl);
} else {
throw new AssertionError("Template fallback logic fails for: " + resourceUrl);
}
} catch (URISyntaxException e) {
throw new IOException(e);
}
return new InputStreamReader(in, StandardCharsets.UTF_8);
}
private static InputStream inputStreamFromJar(URL resourceUrl)
throws URISyntaxException, IOException {
// Jar URLs look like this: jar:file:/path/to/file.jar!/entry/within/jar
// So take apart the URL to open the jar /path/to/file.jar and read the entry
// entry/within/jar from it.
String resourceUrlString = resourceUrl.toString().substring("jar:".length());
int bang = resourceUrlString.lastIndexOf('!');
String entryName = resourceUrlString.substring(bang + 1);
if (entryName.startsWith("/")) {
entryName = entryName.substring(1);
}
URI jarUri = new URI(resourceUrlString.substring(0, bang));
JarFile jar = new JarFile(new File(jarUri));
JarEntry entry = jar.getJarEntry(entryName);
InputStream in = jar.getInputStream(entry);
// We have to be careful not to close the JarFile before the stream has been read, because
// that would also close the stream. So we defer closing the JarFile until the stream is closed.
return new FilterInputStream(in) {
@Override
public void close() throws IOException {
super.close();
jar.close();
}
};
}
// We don't really expect this case to arise, since the bug we're working around concerns jars
// not individual files. However, when running the test for this workaround from Maven, we do
// have files. That does mean the test is basically useless there, but Google's internal build
// system does run it using a jar, so we do have coverage.
private static InputStream inputStreamFromFile(URL resourceUrl)
throws IOException, URISyntaxException {
File resourceFile = new File(resourceUrl.toURI());
return new FileInputStream(resourceFile);
}
private static Object fieldValue(Field field, Object container) {
try {
return field.get(container);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
private static boolean isStaticFinal(Field field) {
int modifiers = field.getModifiers();
return Modifier.isStatic(modifiers) && Modifier.isFinal(modifiers);
}
}