Develop Reference

How to return the result in Map in PL/SQL?

I want to return a map to my Java code from a stored procedure. The results from PL/SQL in a Map format like Map<key, List>. Is it possible to return data like that?
I have returned the whole data in a string and from java class I have used split logic to split the data and saved them in proper fields. Like an example:
String[] lines = resultString.split(System.lineSeparator()); List<MessageVO> resultPerList = new ArrayList<>();
for (String line : lines) {
MessageVO message = new MessageVO();
String[] fieldArray = line.split(":", 0);
String field= fieldArray[0];
message.setField(field);
resultPerList.add(message);
}

If you like PL/SQL and the resulting lists are small, your solution (structuring data in SQL) is good. In PL/SQL you can take advantage of the listagg statement
Here is functional sample:
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class sasafd {
public static void main(String[] args) {
String resultString = "key1:valuea:valueb:valuec"
+ System.lineSeparator()
+ "key2:valuea:valueb:valuec";
String[] lines = resultString.split(System.lineSeparator());
Map<String, List<String>> resultMap = new HashMap<String, List<String>>();
for (String line : lines) {
String[] fieldArray = line.split(":", 0);
for (String value : fieldArray)
if (resultMap.containsKey(fieldArray[0])) {
resultMap.get(fieldArray[0]).add(value);
} else {
resultMap.put(fieldArray[0], new LinkedList<String>());
}
}
System.out.println(convertWithStream(resultMap));
}
public static String convertWithStream(Map<String, List<String>> map) {
String mapAsString = map.keySet().stream().map(key -> key + "=" + map.get(key))
.collect(Collectors.joining(", ", "{", "}"));
return mapAsString;
}
}
Output:
{key1=[valuea, valueb, valuec], key2=[valuea, valueb, valuec]}
If you like more tabular data, from DB you can use thoughts from this code:
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class sasafd {
public static void main(String[] args) {
String[][] resultSet =
{{"key1","valuea"},{"key1","valueb"},{"key1","valuec"}
,{"key2","valuea"},{"key2","valueb"},{"key2","valuec"}};
Map<String, List<String>> resultMap = new HashMap<String, List<String>>();
for (String[] line : resultSet) {
if (resultMap.containsKey(line[0])) {
resultMap.get(line[0]).add(line[1]);
} else {
resultMap.put(line[0], new LinkedList<String>());
resultMap.get(line[0]).add(line[1]);
}
}
System.out.println(convertWithStream(resultMap));
}
public static String convertWithStream(Map<String, List<String>> map) {
String mapAsString = map.keySet().stream().map(key -> key + "=" + map.get(key))
.collect(Collectors.joining(", ", "{", "}"));
return mapAsString;
}
}
You can also try ORM. If you dislike colon-separated text from PL/SQL you can also use XML, JSON, ...
JDBC doesn't support Map results.

How to append to JSON with Java and Jackson

I'm trying a simple test where the code appends a few json entries, however it is getting overwritten each time (the json file will only have 1 entry in it after running). I know I need to somehow create an array in JSON using '[]', but how would I go about doing that? Also, is there a better way to be doing this? I've been searching around and every library seems clunky with lots of user written code. Thanks
public class REEEE {
private static Staff createStaff() {
Staff staff = new Staff();
staff.setName("mkyong");
staff.setAge(38);
staff.setPosition(new String[] { "Founder", "CTO", "Writer" });
Map<String, Double> salary = new HashMap() {
{
put("2010", 10000.69);
}
};
staff.setSalary(salary);
staff.setSkills(Arrays.asList("java", "python", "node", "kotlin"));
return staff;
}
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
File file = new File("src//j.json");
for(int i = 0; i < 4; i++) {
Staff staff = createStaff();
try {
// Java objects to JSON file
mapper.writeValue(file, staff);
// Java objects to JSON string - compact-print
String jsonString = mapper.writeValueAsString(staff);
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

You can add staff in List and then write the list to file as below,
List<Staff> staffList = new LinkedList<>()
for(int i = 0; i < 4; i++) {
Staff staff = createStaff();
staffList.add(staff);
}
mapper.writeValue(file, staffList);
Hope it helps.

Jackson was implemented to parse and generate JSON payloads. All extra logic related with adding new element to array and writing back to file you need to implement yourself. It should not be hard to do:
class JsonFileAppender {
private final ObjectMapper jsonMapper;
public JsonFileAppender() {
this.jsonMapper = JsonMapper.builder().build();
}
public void appendToArray(File jsonFile, Object value) throws IOException {
Objects.requireNonNull(jsonFile);
Objects.requireNonNull(value);
if (jsonFile.isDirectory()) {
throw new IllegalArgumentException("File can not be a directory!");
}
JsonNode node = readArrayOrCreateNew(jsonFile);
if (node.isArray()) {
ArrayNode array = (ArrayNode) node;
array.addPOJO(value);
} else {
ArrayNode rootArray = jsonMapper.createArrayNode();
rootArray.add(node);
rootArray.addPOJO(value);
node = rootArray;
}
jsonMapper.writeValue(jsonFile, node);
}
private JsonNode readArrayOrCreateNew(File jsonFile) throws IOException {
if (jsonFile.exists() && jsonFile.length() > 0) {
return jsonMapper.readTree(jsonFile);
}
return jsonMapper.createArrayNode();
}
}
Example usage with some usecases:
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.json.JsonMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
public class JsonPathApp {
public static void main(String[] args) throws Exception {
Path jsonTmpFile = Files.createTempFile("json", "array");
JsonFileAppender jfa = new JsonFileAppender();
// Add POJO
jfa.appendToArray(jsonTmpFile.toFile(), createStaff());
printContent(jsonTmpFile); //1
// Add primitive
jfa.appendToArray(jsonTmpFile.toFile(), "Jackson");
printContent(jsonTmpFile); //2
// Add another array
jfa.appendToArray(jsonTmpFile.toFile(), Arrays.asList("Version: ", 2, 10, 0));
printContent(jsonTmpFile); //3
// Add another object
jfa.appendToArray(jsonTmpFile.toFile(), Collections.singletonMap("simple", "object"));
printContent(jsonTmpFile); //4
}
private static Staff createStaff() {
Staff staff = new Staff();
staff.setName("mkyong");
staff.setAge(38);
staff.setPosition(new String[]{"Founder", "CTO", "Writer"});
Map<String, Double> salary = new HashMap<>();
salary.put("2010", 10000.69);
staff.setSalary(salary);
staff.setSkills(Arrays.asList("java", "python", "node", "kotlin"));
return staff;
}
private static void printContent(Path path) throws IOException {
List<String> lines = Files.readAllLines(path);
System.out.println(String.join("", lines));
}
}
Above code prints 4 lines:
1
[{"name":"mkyong","age":38,"position":["Founder","CTO","Writer"],"salary":{"2010":10000.69},"skills":["java","python","node","kotlin"]}]
2
[{"name":"mkyong","age":38,"position":["Founder","CTO","Writer"],"salary":{"2010":10000.69},"skills":["java","python","node","kotlin"]},"Jackson"]
3
[{"name":"mkyong","age":38,"position":["Founder","CTO","Writer"],"salary":{"2010":10000.69},"skills":["java","python","node","kotlin"]},"Jackson",["Version: ",2,10,0]]
4
[{"name":"mkyong","age":38,"position":["Founder","CTO","Writer"],"salary":{"2010":10000.69},"skills":["java","python","node","kotlin"]},"Jackson",["Version: ",2,10,0],{"simple":"object"}]

Parse JSON into Object

I have a User class defined as:
User.java
package model;
import java.util.List;
import java.util.Map;
public class User {
private final Map<String, List<String>> accountTransactionsMap;
public User(final Map<String, List<String>> accountTransactionsMap) {
this.accountTransactionsMap = accountTransactionsMap;
}
public Map<String, List<String>> getAccountTransactionsMap() {
return accountTransactionsMap;
}
}
I am calling a REST API that returns the following response:
{
"username1":{
"456":[
],
"123":[
],
"789":[
]
},
"username2":{
"123":[
],
"456":[
],
"789":[
]
},
"username3":{
"789":[
],
"123":[
],
"456":[
"transaction10",
"transaction6",
"transaction9",
"transaction3"
]
}
}
I would like to be able to parse through the response and store it in a User object.
I have tried the following:
Test.java
public class Test {
public static void main(final String[] args) {
final String response = "{\"username1\":{\"456\":[],\"123\":[],\"789\":[]},\"username2\":{\"123\":[],\"456\":[],\"789\":[]},\"username3\":{\"789\":[],\"123\":[],\"456\":[\"transaction10\",\"transaction6\",\"transaction9\",\"transaction3\"]}}";
final Gson gson = new Gson();
final Type map = new TypeToken<Map<String, User>>(){}.getType();
final Map<String, User> result = gson.fromJson(response, map);
System.out.println(result);
if (result != null) {
for (final Map.Entry<String, User> entry : result.entrySet()) {
System.out.println("username: " + entry.getKey());
final User user = entry.getValue();
System.out.println("transactions: " + user.getAccountTransactionsMap());
}
}
}
}
This yields output:
{username1=model.User#80ec1f8, username2=model.User#1445d7f, username3=model.User#6a396c1e}
username: username1
transactions: null
username: username2
transactions: null
username: username3
transactions: null
I expect output:
{username1=model.User#80ec1f8, username2=model.User#1445d7f, username3=model.User#6a396c1e}
username: username1
transactions: {123=[],456=[],789=[]}
username: username2
transactions: {123=[],456=[],789=[]}
username: username3
transactions: {123=[],456=["transaction10", "transaction6", "transaction9", "transaction3"],789=[]}
How can I parse the accountId and the list of transactionIds into its own map as a variable in my User class?
Edit: I suppose the question really becomes, how can I create a custom TypeToken for my User class?

Instead of User class you need to use Map<String, Map<String, List<String>>>:
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import java.io.File;
import java.io.FileReader;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;
public class GsonApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
final Gson gson = new Gson();
final Type map = new TypeToken<Map<String, Map<String, List<String>>>>(){}.getType();
final Map<String, Map<String, List<String>>> result = gson.fromJson(new FileReader(jsonFile), map);
System.out.println(result);
if (result != null) {
for (final Map.Entry<String, Map<String, List<String>>> entry : result.entrySet()) {
System.out.println("username: " + entry.getKey());
final Map<String, List<String>> user = entry.getValue();
System.out.println("transactions: " + user);
}
}
}
}
Above code prints:
{username1={456=[], 123=[], 789=[]}, username2={123=[], 456=[], 789=[]}, username3={789=[], 123=[], 456=[transaction10, transaction6, transaction9, transaction3]}}
username: username1
transactions: {456=[], 123=[], 789=[]}
username: username2
transactions: {123=[], 456=[], 789=[]}
username: username3
transactions: {789=[], 123=[], 456=[transaction10, transaction6, transaction9, transaction3]}
If you really need, you can create User object after parsing.

Unable to parse the key and value of nested json file using java

Below is the json file i am trying to parse.I want to print all key and corresponding values.
{
"A":{
"name":"Ram",
"gender":"male",
"designation":"engineer"
},
"B":{
"name":"Shyam",
"gender":"male",
"designation":"student"
},
"C":{
"name":"Mohan",
"gender":"male",
"designation":"manager"
}
}
I have tried the following code:
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Iterator;
import org.json.JSONArray;
import org.json.JSONObject;
import org.json.simple.parser.JSONParser;
public class FetchJsonNested {
public static void main(String args[]) throws FileNotFoundException {
try {
JSONParser jp=new JSONParser();
Object obj=jp.parse(new FileReader("C:\\Users\\DELL\\Documents\\NetBeansProjects\\WaterNetwork\\web\\kusharray.json"));
JSONObject job=(JSONObject)obj;
Iterator < ? > keys = job.keys();
while (keys.hasNext()) {
String key = (String) keys.next();
System.out.println(key);
if (job.get(key) instanceof JSONObject) {
System.out.println(job.get(key));
}
}
} catch(Exception e) {
e.printStackTrace();
}
}
}
I have read stuffs from many site but no one is working like the way i want.I want to print all keys and corresponding values.

Using org.json as you did in your example :
String jsonStr = "{\"A\":{\"name\":\"Ram\",\"gender\":\"male\",\"designation\":\"engineer\"},\"B\":{\"name\":\"Shyam\",\"gender\":\"male\",\"designation\":\"student\"},\"C\":{\"name\":\"Mohan\",\"gender\":\"male\",\"designation\":\"manager\"}}";
JSONObject json = new JSONObject(jsonStr);
for (Object key : json.keySet().toArray()){
JSONObject data = json.getJSONObject(key.toString());
System.out.println("json :" + data.toString());
System.out.println("name :" +data.getString("name"));
System.out.println("gender :" +data.getString("gender"));
System.out.println("designation :" +data.getString("designation"));
}
Now you can replace my first line "String jsonStr = ..." with your file reader.

below follow not the awesome and most elegant solution but this can lead you to what you need.
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;
public class Main {
public static void main(String[] args) throws Exception {
String jsonString = loadJSONFile();
JsonElement jsonElement = new JsonParser().parse(jsonString);
JsonObject jsonObject = jsonElement.getAsJsonObject();
print(jsonObject);
}
private static String loadJSONFile() throws FileNotFoundException {
Scanner scanner = new Scanner(new FileReader("path/to/the/json/file.ext"));
StringBuilder stringBuilder = new StringBuilder();
while (scanner.hasNext()) {
stringBuilder.append(scanner.next());
}
scanner.close();
return stringBuilder.toString();
}
private static void print(JsonObject jsonObject) {
Set<Map.Entry<String, JsonElement>> entries = jsonObject.entrySet();
for (Map.Entry<String, JsonElement> entry : entries) {
System.out.println(entry.getKey() + ": " + entry.getValue());
try {
JsonElement jsonElement = new JsonParser().parse(String.valueOf(entry.getValue()));
JsonObject innerJsonObject = jsonElement.getAsJsonObject();
print(innerJsonObject);
} catch (Exception e) {
// is not a JSON
}
}
}
}
Output example:
A: {"name":"Ram","gender":"male","designation":"engineer"}
name: "Ram"
gender: "male"
designation: "engineer"
B: {"name":"Shyam","gender":"male","designation":"student"}
name: "Shyam"
gender: "male"
designation: "student"
C: {"name":"Mohan","gender":"male","designation":"manager"}
name: "Mohan"
gender: "male"
designation: "manager"

how to iterate through hashmap and store entities into mysql

sorry I am a newbie I have been looking for an example on how I can iterate hashmap and store the entities into MySQL database. the blow code downloads currency rate which I would like to store into my database. the output is
{CCY=USD, RATE=1.5875}
{CCY=EUR, RATE=1.1919}
{CCY=ALL, RATE=166.2959}
{CCY=AMD, RATE=645.4025}
how can I iterate the HashMap and store it into my database? an illustration would be nice or source similar to this scenario.
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
public class Rate {
/** list of string array containing IOSCurrencyCodes*/
final String[] CURRENCY = new String[] { "USD","EUR","ALL","AMD",};
#SuppressWarnings("rawtypes")
void checkRateAllAtEnd() throws Exception {
List<Callable<HashMap>> tasks = new ArrayList<Callable<HashMap>>();
for (final String ccy : CURRENCY) {
tasks.add(new Callable<HashMap>() {
public HashMap<String, Comparable> call() throws Exception {
return getRates(ccy);
}
});
}
ExecutorService executorPool = Executors.newCachedThreadPool();
final List<Future<HashMap>> listRates = executorPool.invokeAll(tasks, 3600, TimeUnit.SECONDS);
for (Future<HashMap> rate : listRates) {
HashMap ccyRate = rate.get();
System.out.println(ccyRate);
}
}
#SuppressWarnings("rawtypes")
public HashMap<String, Comparable> getRates(String ccy) throws Exception {
URL url = new URL("http://finance.yahoo.com/d/quotes.csv?e=.csv&f=sl1d1t1&s=GBP"
+ ccy + "=X");
BufferedReader reader = new BufferedReader(new InputStreamReader(
url.openStream()));
String data = reader.readLine();
String[] dataItems = data.split(",");
Double rate = Double.valueOf(dataItems[1]);
HashMap<String, Comparable> ccyRate = new HashMap<String, Comparable>();
ccyRate.put("CCY", ccy);
ccyRate.put("RATE", rate);
return ccyRate;
}
public static void main(String[] args) {
Rate ccyRate = new Rate();
try {
//ccyConverter.checkRateSequential();
ccyRate.checkRateAllAtEnd();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

Map provides entrySet method which is very useful to iterate over a map.
Map#entrySet returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress.
ref - link
Code -
HashMap<String, Comparable> ccyRate = new HashMap<String, Comparable>();
for(Map.Entry<String, Comparable> entry: ccyRate.entrySet){
System.out.println(entry.getKey()+" - "+entry.getValue());
}