Gson到普通旧Java对象（POJO）
我已经阅读了GSon用户指南，并在这里查看了一些问题，但我真的很难理解为什么在尝试使用GSon创建java对象时出错Gson到普通旧Java对象（POJO）,java,json,pojo,Java,Json,Pojo,我已经阅读了GSon用户指南，并在这里查看了一些问题，但我真的很难理解为什么在尝试使用GSon创建java对象时出错 public class TestJSON extends ActionBarActivity { private Location start; private String length; private String url = "http://maps.googleapis.com/maps/api/directions/json?origin="
public class TestJSON extends ActionBarActivity {
private Location start;
private String length;
private String url = "http://maps.googleapis.com/maps/api/directions/json?origin=";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test_json);
// dummyprovider is provided by google to let me set a location.
start = new Location("dummyprovider");
start.setLatitude(51.5033630);
start.setLongitude(-0.1276250);
// Recieve an android warning if you run a retrieval task (such as JSON)
// in the main thread).
try {
System.out.println("printing Json");
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
try {
toJava(readJsonFromUrl(urlBuilder()));
} catch (Exception e) {
e.printStackTrace();
}
}
});
thread.start();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.test_json, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
// I think in future I will call this function a ton of times and send it
// some locations as waypoints for it to try and get closer to the
// distances.
private String urlBuilder() {
String newUrl = url + start.getLatitude() + "," + start.getLongitude()
+ "&destination=51.5042178,23";
return newUrl;
}
// Builds the string for JSON.
private String readAll(Reader rd) throws IOException {
StringBuilder sb = new StringBuilder();
int cp;
while ((cp = rd.read()) != -1) {
sb.append((char) cp);
}
return sb.toString();
}
// Take an input url and reads from it using the url above. We then put it
// into a JSON object.
private JSONObject readJsonFromUrl(String url) throws IOException,
JSONException {
InputStream is = new URL(url).openStream();
try {
BufferedReader rd = new BufferedReader(new InputStreamReader(is,
Charset.forName("UTF-8")));
String jsonText = readAll(rd);
JSONObject json = new JSONObject(jsonText);
return json;
} finally {
is.close();
}
}
private void toJava(JSONObject obj) throws Exception {
Gson gson = new Gson();
MapsRoute m = gson.fromJson(readJsonFromUrl(urlBuilder()).toString(),
MapsRoute.class);
System.out.println(m);
}
}
public class MapsRoute {
@SerializedName("routes")
public List<String> routes;
@SerializedName("copyrights")
public String copyrights;
@SerializedName("legs")
public List<String> legs;
@SerializedName("steps")
public List<String> steps;
}
tW]@cADYD[DUBWFy@PWD}，“行驶模式”：“驾驶”，“开始位置”：{“lng”：-0.1262498，“lat”：51.5034032}}，{“html_指令”：“转弯”
马上到马卫那里去
平均值，持续时间：{“值”：53，“文本”：“1”
最小“}”，距离：{“值”：242，“文本”：“0.2”
km“}”，终点位置：{“lng”：-0.1231268，“lat”：51.504648900001}，“多段线”：{“点”：“{pjyHxuWC]Ei@IgAAQAOAMAK橡木？M？M？K？I？I@I?M@SWxH”~Ab@H嘿，Java对象与json的映射是不正确的
示例：routes有边界、分支、版权、步骤，而不是上面代码中映射的方式。不看任何东西，
期望一个字符串，但BEGIN\u OBJECTreadJsonFromUrl（）返回的json
字符串的ct 09-24 19:22:47.367: W/System.err(1720): com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 27
09-24 19:22:47.367: W/System.err(1720): at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:176)
09-24 19:22:47.367: W/System.err(1720): at com.google.gson.Gson.fromJson(Gson.java:803)
09-24 19:22:47.367: W/System.err(1720): at com.google.gson.Gson.fromJson(Gson.java:768)
09-24 19:22:47.367: W/System.err(1720): at com.google.gson.Gson.fromJson(Gson.java:717)
09-24 19:22:47.367: W/System.err(1720): at com.google.gson.Gson.fromJson(Gson.java:689)
09-24 19:22:47.367: W/System.err(1720): at boyle.matt.runrouter.TestJSON.toJava(TestJSON.java:119)
09-24 19:22:47.367: W/System.err(1720): at boyle.matt.runrouter.TestJSON.access$2(TestJSON.java:117)
09-24 19:22:47.371: W/System.err(1720): at boyle.matt.runrouter.TestJSON$1.run(TestJSON.java:47)
09-24 19:22:47.371: W/System.err(1720): at java.lang.Thread.run(Thread.java:856)
09-24 19:22:47.371: W/System.err(1720): Caused by: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 27
09-24 19:22:47.371: W/System.err(1720): at com.google.gson.stream.JsonReader.nextString(JsonReader.java:821)
09-24 19:22:47.371: W/System.err(1720): at com.google.gson.internal.bind.TypeAdapters$13.read(TypeAdapters.java:358)
09-24 19:22:47.371: W/System.err(1720): at com.google.gson.internal.bind.TypeAdapters$13.read(TypeAdapters.java:346)
09-24 19:22:47.371: W/System.err(1720): at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40)
09-24 19:22:47.371: W/System.err(1720): at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:81)
09-24 19:22:47.371: W/System.err(1720): at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:60)
09-24 19:22:47.371: W/System.err(1720): at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93)
09-24 19:22:47.371: W/System.err(1720): at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172)
09-24 19:22:47.371: W/System.err(1720): ... 8 more