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Merge pull request #161 from sparkprime/java_comparison
Java comparison
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‎doc/language/java_comparison/.gitignore

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*.class

‎doc/language/java_comparison/BaseTemplate.java

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/*
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Copyright 2016 Google Inc. All rights reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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import java.util.Arrays;
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import java.util.HashSet;
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import java.util.Set;
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public class BaseTemplate extends JsonnetObject {
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public Set<String> nonHiddenFields() {
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Set<String> r = super.nonHiddenFields();
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r.addAll(Arrays.asList("apiVersion", "kind", "spec"));
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return r;
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}
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// Mandatory param
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public Object accessToken() {
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throw new RuntimeException("accessToken must be defined");
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}
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// Optional params
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public Object image() { return "gcr.io/cooltool-1009/pipeline_image:latest"; }
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public Object[] extraEnv() { return new Object[]{}; }
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public Object apiVersion() { return "v1"; }
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public Object kind() { return "ReplicationController"; }
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public class BaseTemplateSpec extends JsonnetObject {
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public Set<String> nonHiddenFields() {
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Set<String> r = super.nonHiddenFields();
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r.addAll(Arrays.asList("replicas", "spec"));
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return r;
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}
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public Object replicas() { return 1.0; }
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public class BaseTemplateSpecSpec extends JsonnetObject {
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public Set<String> nonHiddenFields() {
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Set<String> r = super.nonHiddenFields();
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r.addAll(Arrays.asList("containers"));
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return r;
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}
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public class Container0 extends JsonnetObject {
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public Set<String> nonHiddenFields() {
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Set<String> r = super.nonHiddenFields();
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r.addAll(Arrays.asList("env", "image", "name"));
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return r;
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}
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class Env0 extends JsonnetObject {
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public Set<String> nonHiddenFields() {
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Set<String> r = super.nonHiddenFields();
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r.addAll(Arrays.asList("name", "value"));
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return r;
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}
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public Object name() { return "ACCESSTOKEN"; }
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public Object value() { return BaseTemplate.this.accessToken(); }
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}
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public Object[] env() {
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// Concatenating arrays (first + second) is hard in Java.
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Object[] first = new Object[]{ new Env0() };
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Object[] second = BaseTemplate.this.extraEnv();
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Object[] result = Arrays.copyOf(first, first.length + second.length);
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System.arraycopy(second, 0, result, first.length, second.length);
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return result;
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}
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public Object image() { return BaseTemplate.this.image(); }
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public Object name() { return "twitter-to-redis"; }
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}
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public Object containers() { return new Object[] { new Container0() }; }
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}
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public Object spec() { return new BaseTemplateSpecSpec(); }
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}
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public Object spec() { return new BaseTemplateSpec(); }
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}
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‎doc/language/java_comparison/JsonnetObject.java

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/*
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Copyright 2016 Google Inc. All rights reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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import java.util.HashSet;
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import java.util.Set;
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public class JsonnetObject {
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public Set<String> nonHiddenFields() { return new HashSet<String>(){}; }
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}

‎doc/language/java_comparison/JsonnetValue.java

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/*
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Copyright 2016 Google Inc. All rights reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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import java.lang.reflect.Method;
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import java.lang.reflect.InvocationTargetException;
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import java.util.HashSet;
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import java.util.Set;
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public class JsonnetValue {
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public static String manifest(Object value) {
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StringBuffer buf = new StringBuffer();
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if (value == null) {
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// FIXME: does not escape the string
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buf.append("null");
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} else if (value instanceof String) {
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// FIXME: does not escape the string
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buf.append("\"" + value + "\"");
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} else if (value instanceof Double) {
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buf.append(value.toString());
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} else if (value instanceof Boolean) {
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buf.append(value.toString());
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} else if (value instanceof Object[]) {
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Object[] arr = (Object[]) value;
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buf.append("[");
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String prefix = " ";
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for (Object element : arr) {
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buf.append(prefix);
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prefix = ", ";
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buf.append(manifest(element));
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}
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buf.append(" ]");
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} else if (value instanceof JsonnetObject) {
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JsonnetObject obj = (JsonnetObject) value;
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buf.append("{");
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String prefix = " ";
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for (String field : obj.nonHiddenFields()) {
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buf.append(prefix);
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prefix = ", ";
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buf.append("\"" + field + "\": ");
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try {
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Method method = obj.getClass().getMethod(field);
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Object fieldValue = method.invoke(obj);
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buf.append(manifest(fieldValue));
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} catch (IllegalArgumentException e) {
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System.out.println(e);
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} catch (IllegalAccessException e) {
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System.out.println(e);
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} catch (InvocationTargetException e) {
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System.out.println(e);
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} catch (SecurityException e) {
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System.out.println(e);
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} catch (NoSuchMethodException e) {
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System.out.println(e);
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}
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}
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buf.append(" }");
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} else {
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throw new RuntimeException("Got weird type: " + value.getClass());
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}
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return buf.toString();
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}
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}
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‎doc/language/java_comparison/README.md

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Jsonnet to Java
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---------------
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This little code example shows how a Jsonnet config using object-oriented features can be
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transliterated (in a structure-preserving manner) to use the object-oriented features of Java. Not
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all Jsonnet programs can be converted to Java because Jsonnet has mixins and virtual inner classes.
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The semantics are also different, as Jsonnet is lazy and Java is eager. Likewise, Java programs
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cannot all be converted to Jsonnet because they have mutable state and I/O.
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However said all this, there is a significant overlap between the two languages. This example fits
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within that overlap.
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Execute Jsonnet code
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--------------------
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```
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jsonnet sub-template.jsonnet
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```
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Execute Java code
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-----------------
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We pipe into jsonnet - to pretty-print the output JSON.
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```
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javac *.java && java Test | jsonnet -
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```
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Structure of Java code
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----------------------
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The translation is as as follows:
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* Everything is typed as Object, as Jsonnet is dynamically typed.
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* Jsonnet arrays are Object[], and primitives are Boolean / Double / String.
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* Jsonnet objects because singleton instances of Java classes that extend JsonnetObject.
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* Jsonnet fields become Java methods with no parameters (fields are virtual in Jsonnet).
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* Jsonnet hidden field status is represented with a method nonHiddenFields which returns a set of
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field names. Other fields are considered hidden.
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* There are 2 liberties taken -- output strings are not escaped properly, and the JSON is printed on
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a single line instead of pretty-printed with indenting.
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The Java code has a number of auxiliary framework functions to provide Jsonnet functionality that is
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implicit in the Jsonnet language.
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* The Test class chooses an object and manifests it to stdout.
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* The JsonnetValue class implements manifestation, as a visitor over possible JSON values that
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builds JSON strings. For objects, it iterates over the non-hidden fields and manifests each value
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by reflectively calling that function.
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Reference JSON
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--------------
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For reference, the JSON that should be output is given in sub-template.json

‎doc/language/java_comparison/SubTemplate.java

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/*
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Copyright 2016 Google Inc. All rights reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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public class SubTemplate extends BaseTemplate {
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// Supply my access token and pinned version.
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public String accessToken() {
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return "xxxxx";
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}
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public String image() {
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return "gcr.io/cooltool-1009/pipeline_image@sha256:....";
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}
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public class SubTemplateSpec extends BaseTemplate.BaseTemplateSpec {
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public Object replicas() { return 2.0; }
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}
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public Object spec() {
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return new SubTemplateSpec();
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}
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}

‎doc/language/java_comparison/Test.java

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/*
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Copyright 2016 Google Inc. All rights reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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public class Test {
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public static void main(String[] args) {
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System.out.println(JsonnetValue.manifest(new SubTemplate()));
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}
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}

‎doc/language/java_comparison/base-template.jsonnet

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/*
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Copyright 2016 Google Inc. All rights reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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{
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// Mandatory param
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accessToken:: error "accessToken must be defined",
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// Optional params
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image:: "gcr.io/cooltool-1009/pipeline_image:latest",
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extraEnv:: [],
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apiVersion: "v1",
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kind: "ReplicationController",
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spec: {
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replicas: 1,
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spec: {
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containers: [
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{
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env: [
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{
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name: "ACCESSTOKEN",
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value: $.accessToken,
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},
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] + $.extraEnv,
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image: $.image,
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name: "twitter-to-redis",
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},
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],
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},
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},
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}

‎doc/language/java_comparison/sub-template.json

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{
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"apiVersion": "v1",
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"kind": "ReplicationController",
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"spec": {
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"replicas": 2,
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"spec": {
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"containers": [
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{
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"env": [
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{
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"name": "ACCESSTOKEN",
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"value": "xxxxx"
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}
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],
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"image": "gcr.io/cooltool-1009/pipeline_image@sha256:....",
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"name": "twitter-to-redis"
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}
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]
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}
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}
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}

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