001/* 002 * Copyright 2018 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.batch.item.json; 018 019import java.util.Iterator; 020import java.util.List; 021 022import org.springframework.batch.item.support.AbstractFileItemWriter; 023import org.springframework.core.io.Resource; 024import org.springframework.util.Assert; 025import org.springframework.util.ClassUtils; 026 027/** 028 * Item writer that writes data in json format to an output file. The location 029 * of the output file is defined by a {@link Resource} and must represent a 030 * writable file. Items are transformed to json format using a 031 * {@link JsonObjectMarshaller}. Items will be enclosed in a json array as follows: 032 * 033 * <p> 034 * <code> 035 * [ 036 * {json object}, 037 * {json object}, 038 * {json object} 039 * ] 040 * </code> 041 * </p> 042 * 043 * The implementation is <b>not</b> thread-safe. 044 * 045 * @see GsonJsonObjectMarshaller 046 * @see JacksonJsonObjectMarshaller 047 * @param <T> type of object to write as json representation 048 * @author Mahmoud Ben Hassine 049 * @since 4.1 050 */ 051public class JsonFileItemWriter<T> extends AbstractFileItemWriter<T> { 052 053 private static final char JSON_OBJECT_SEPARATOR = ','; 054 private static final char JSON_ARRAY_START = '['; 055 private static final char JSON_ARRAY_STOP = ']'; 056 057 private JsonObjectMarshaller<T> jsonObjectMarshaller; 058 059 /** 060 * Create a new {@link JsonFileItemWriter} instance. 061 * @param resource to write json data to 062 * @param jsonObjectMarshaller used to marshal object into json representation 063 */ 064 public JsonFileItemWriter(Resource resource, JsonObjectMarshaller<T> jsonObjectMarshaller) { 065 Assert.notNull(resource, "resource must not be null"); 066 Assert.notNull(jsonObjectMarshaller, "json object marshaller must not be null"); 067 setResource(resource); 068 setJsonObjectMarshaller(jsonObjectMarshaller); 069 setHeaderCallback(writer -> writer.write(JSON_ARRAY_START)); 070 setFooterCallback(writer -> writer.write(this.lineSeparator + JSON_ARRAY_STOP + this.lineSeparator)); 071 setExecutionContextName(ClassUtils.getShortName(JsonFileItemWriter.class)); 072 } 073 074 /** 075 * Assert that mandatory properties (jsonObjectMarshaller) are set. 076 * 077 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet() 078 */ 079 @Override 080 public void afterPropertiesSet() throws Exception { 081 if (this.append) { 082 this.shouldDeleteIfExists = false; 083 } 084 } 085 086 /** 087 * Set the {@link JsonObjectMarshaller} to use to marshal object to json. 088 * @param jsonObjectMarshaller the marshaller to use 089 */ 090 public void setJsonObjectMarshaller(JsonObjectMarshaller<T> jsonObjectMarshaller) { 091 this.jsonObjectMarshaller = jsonObjectMarshaller; 092 } 093 094 @Override 095 public String doWrite(List<? extends T> items) { 096 StringBuilder lines = new StringBuilder(); 097 Iterator<? extends T> iterator = items.iterator(); 098 if (!items.isEmpty() && state.getLinesWritten() > 0) { 099 lines.append(JSON_OBJECT_SEPARATOR).append(this.lineSeparator); 100 } 101 while (iterator.hasNext()) { 102 T item = iterator.next(); 103 lines.append(' ').append(this.jsonObjectMarshaller.marshal(item)); 104 if (iterator.hasNext()) { 105 lines.append(JSON_OBJECT_SEPARATOR).append(this.lineSeparator); 106 } 107 } 108 return lines.toString(); 109 } 110 111}