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@jhorstmann
Created November 12, 2012 22:41
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Getting familiar with the JsonBuilder API of JSR 353
package net.jhorstmann.jsonp;
import java.io.IOException;
import java.io.PushbackReader;
import java.io.StringReader;
import javax.json.JsonArray;
import javax.json.JsonArrayBuilder;
import javax.json.JsonBuilder;
import javax.json.JsonBuilder.JsonBuildable;
import javax.json.JsonObject;
import javax.json.JsonObjectBuilder;
import javax.json.JsonStructure;
/**
* Trying to get familiar with the proposed API of JSR353,
* this code uses JsonBuilder inside a recursive descent parser
* for a simple JSON-like format that consists of arrays,
* objects with single-character keys and single digit numbers.
*/
public class RecurseiveParsingWithJsonBuilder {
/**
* Parses an object with an object as parent.
*/
public static void readObject(PushbackReader reader, JsonObjectBuilder parentBuilder, String key) throws IOException {
JsonObjectBuilder objectBuilder = parentBuilder.beginObject(key);
readObject0(reader, objectBuilder);
objectBuilder.endObject();
}
/**
* Parses an object with an array as parent.
*/
public static void readObject(PushbackReader reader, JsonArrayBuilder parentBuilder) throws IOException {
JsonObjectBuilder objectBuilder = parentBuilder.beginObject();
readObject0(reader, objectBuilder);
objectBuilder.endObject();
}
private static void readObject0(PushbackReader reader, JsonObjectBuilder objectBuilder) throws IOException {
int ch = reader.read();
if (ch == -1) {
throw new IOException("unexpected eof");
} else if (ch != '}') {
reader.unread(ch);
while (true) {
ch = reader.read();
if (ch >= 'a' || ch <= '9') {
String key = "" + (char) ch;
ch = reader.read();
if (ch == -1) {
throw new IOException("unexpected eof");
} else if (ch != ':') {
throw new IOException("unexpected char " + (char) ch);
} else {
ch = reader.read();
if (ch == -1) {
throw new IOException("unexpected eof");
} else if (ch == '[') {
readArray(reader, objectBuilder, key);
} else if (ch == '{') {
readObject(reader, objectBuilder, key);
} else if (ch >= '0' && ch <= '9') {
objectBuilder.add(key, ch - '0');
} else {
throw new IOException("unexpected char " + (char) ch);
}
}
} else if (ch == -1) {
throw new IOException("unexpected eof");
}
ch = reader.read();
if (ch == '}') {
break;
} else if (ch == -1) {
throw new IOException("unexpected eof");
} else if (ch != ',') {
throw new IOException("unexpected char " + (char) ch);
}
}
}
}
/**
* Parses an array with an object as parent.
*/
public static void readArray(PushbackReader reader, JsonObjectBuilder parentBuilder, String key) throws IOException {
JsonArrayBuilder arrayBuilder = parentBuilder.beginArray(key);
readArray0(reader, arrayBuilder);
arrayBuilder.endArray();
}
/**
* Parses an array with an array as parent.
*/
public static void readArray(PushbackReader reader, JsonArrayBuilder parentBuilder) throws IOException {
JsonArrayBuilder arrayBuilder = parentBuilder.beginArray();
readArray0(reader, arrayBuilder);
arrayBuilder.endArray();
}
private static void readArray0(PushbackReader reader, JsonArrayBuilder arrayBuilder) throws IOException {
int ch = reader.read();
if (ch == -1) {
throw new IOException("unexpected eof");
} else if (ch != ']') {
reader.unread(ch);
while (true) {
ch = reader.read();
if (ch == '[') {
readArray(reader, arrayBuilder);
} else if (ch == '{') {
readObject(reader, arrayBuilder);
} else if (ch >= '0' && ch <= '9') {
arrayBuilder.add(ch - '0');
} else if (ch == -1) {
throw new IOException("unexpected eof");
} else {
throw new IOException("unexpected char " + (char) ch);
}
ch = reader.read();
if (ch == ']') {
break;
} else if (ch == -1) {
throw new IOException("unexpected eof");
} else if (ch != ',') {
throw new IOException("unexpected char " + (char) ch);
}
}
}
}
/*
* Parses the root element, either an object or an array.
*/
public static JsonStructure readRoot(PushbackReader reader) throws IOException {
int ch = reader.read();
if (ch == '[') {
JsonBuilder builder = new JsonBuilder();
JsonArrayBuilder<JsonBuildable<JsonArray>> arrayBuilder = builder.beginArray();
readArray0(reader, arrayBuilder);
return arrayBuilder.endArray().build();
} else if (ch == '{') {
JsonBuilder builder = new JsonBuilder();
JsonObjectBuilder<JsonBuildable<JsonObject>> objectBuilder = builder.beginObject();
readObject0(reader, objectBuilder);
return objectBuilder.endObject().build();
} else {
throw new IOException("unexpected char " + (char) ch);
}
}
public static JsonStructure readRoot(String data) throws IOException {
PushbackReader reader = new PushbackReader(new StringReader(data));
return readRoot(reader);
}
public static void main(String[] args) throws IOException {
System.out.println(readRoot("[1,2,3,[4],{a:1,b:2,c:{},d:[]},[5,6,{}]]"));
System.out.println(readRoot("{a:[1,2,3,[4],{a:1,b:2,c:{},d:[]},[5,6,{}]]}"));
}
}
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